. - , '.' Y, 7. ,"!. ?' g, . + ,I;r " t. !

PI European Corn r : -I \*'- ? u Development and ' Management Sponsored by the Experiment Authors Agricultural Research Service, USDA, Stations and Extension Services of W. 6.Showers, lowa W. D. Guthrie, research leader, Corn Contents Summary of Colorado, Delaware, Georgia, Illinois, J. F. Witkowski, Nebraska Insects Research Unit, Ankeny, lowa Management Tactics C. E. Mason, Delaware Indiana, lowa, Kansas, Kentucky, Introduction 24 One-generation Regions D. D. Calvin, Pennsylvania Cooperative States Research Service, 24 Two-generation Regions Maryland, Michigan, Minnesota, R. A. Higgins, Kansas USDA, J. A. Naegele, entomologist, The Insect 26 Three- or More-generation Missouri, Nebraska, New York, North G. P. Dively, Maryland Entomology Staff, Washington, D.C. Carolina, North Dakota, Ohio, 4 Identification Regions Pennsylvania, South Carolina, South Technical Committee on Administrative Advisor, F. E. Hutchinson, 8 Life Cycle and Generational Dakota, Wisconsin; and Agricultural Stalk-boring Insects1 vice president, Ohio State University, Ecotypes European Corn Borer on H. C. Chiang, emeritus Research Service, U.S. Department Columbus, Ohio. 11 How Corn Is Damaged by the Commodities Other than F. 6.Peairs, Colorado European Corn Borer Field Corn of Agriculture cooperating. C. E. Mason, Delaware Reviewed for release by David E. Foster, A. N. Sparks, Georgia 26 Sweet Corn former ISU extension entomologist and Components of Management 30 Popcorn In recognition of his numerous contri- E. Levine, Illinois Marlin Rice. ISU extension entomologist. butions to insect ecology, the F. T. Turpin, Indiana 12 Scouting Techniques 31 Peppers W. 6. Showers, lowa authors affectionately dedicate this 'North Central Regional Project NC180; 14 Economic Injury Levels, 31 Snap Beans R. A. Higgins, Kansas Economic Thresholds, and 32 Potato interregional bulletin to Dr. Huai C. G. P. Dively, Maryland Impact of Integrated Crop Management Chiang, emeritus lifetime member, J. M. Scriber, Michigan Practices on European Corn Borer and Reaching a Management 32 Other Crops Related Stalk-boring Insects. Inter- NC-180 Research Committee. D. A. Andow, Minnesota Decision A. J. Keaster, Missouri regional Committee as of June, 1987. 18 Timing Insecticide Treatment J. F. Witkowski, Nebraska NCR 327 replaces NCR 22. 20 Application Equipment C. J. Eckenrode, New York Printed and distributed in coopera- 21 Resistant Varieties J. W. Van Duyn, North Carolina tion with Extension Service, U.S. M. J. Weiss, North Dakota 22 Biological Agents Department of Agriculture, 22 Weather 6.R. Stinner, Ohio Washington, D.C. D. D. Calvin, Pennsylvania 23 Cultural Practices J. A. Durant, South Carolina D. D. Walgenbach, South Dakota J. L. Wedberg, Wisconsin Introduction per year population began to appear The European corn borer (ECB), in the north central states. This two- Ostrinia nubilalis (Hiibner), signifi- generation per year borer spread cantly affects production of Zea rapidly and soon became dominant mays L. (field corn, popcorn, and in the region. It reached Illinois in sweet corn), as well as other com- 1939, Iowa in 1942, Nebraska in mercial host plant species including 1944, and South Dakota in 1946. sorghum, cotton, and many Meanwhile, the single-generation vegetables. borer spread northward into northern Minnesota, North Dakota, and the European corn borer is an intro- Canadian provinces of Quebec, duced insect species that belongs Manitoba, and Saskatchewan. to the order Lepidoptera. It came to North America during the early Three- and four-generation per year 1900s, possibly in broom corn im- populations of European corn borer ported from central Europe. It was dispersed southward along the first found in the north central states Atlantic Coast and southwestward in 1921. It spread slowly from south- into ~issouri,Arkansas, Kansas, ern Michigan and northern Ohio. By Oklahoma, and the Gulf states. Fig- the end of 1938, it was only as far ure 1 shows the approximate current west as the Wisconsin shore of Lake range of the European corn borer in Michigan. the United States and Canada.

During most of this early history, the insect had one generation per year. In the late 1930s, a two-generation (.

Figure 1. Approximate distribution of generations of European corn borer in the United States and Canada.

Generation

I1

Y 1-2 The Insect Table 1. A simple key for identifying some common late-instar caterpillars found on 2. Body without obvious, dense, Figure G. 4. Black central dots in tips of fully corn. (G. L. Godfrey, Illinois Natural History Survey, University of Illinois) "hair-like" covering extended prolegs on abdominal Identification (figure D) go to . . . 3 segments 3 through 6 (figure H), Several species of caterpillars (lar- 1. Prolegs on abdominal segments only on abdominal segments 5, 6, - Body obviously "hairy" visible at 10 power, body pale vae) commonly found in the southern 3, 4, 5, 6,and 10 (anal) and 10 (figure B), or on 6 and 10 (figures E, F, G) . . . woollyworms, brown or pinkish gray with dark and western portions of the north (figure A) go to . . . 2 (figure C) . . . semiloopers or cattail caterpillar, io moth gray middorsal line on abdominal central states might be confused - Fully developed prolegs present loopers caterpillar segments (figure D) . . . European with the European corn borer. Occa- corn borer sionally these caterpillars are found - No black central dots in tips of in the northern portion of the region. Figure A. Figure D. fully extended prolegs on abdomi- Important characteristics are illus- rTHORAXTABDOMEN (10 SEGMENTS 1 nal segments 3 through 6 trated in a simple key developed to (figure I); body off-white go assist with field identification 1 to ...5 I METATHORAX I (table 1). MESOTHORAX 7 3. Crochets (minute hooks) on end 5. Body with large, black tubercles CERVICAL- \ of prolegs 3, 4, 5, and 6 form (figure K,) . . . southwestern corn circle or nearly complete circle borer (summer form) (figures H, I) go to . . . 4 - Body with pale brown tubercles - Crochets on end of prolegs 3, 4, or tubercles inconspicuous 5, and 6 form straight line or arc (figure K,) . . . southwestern corn of less than 270" (figure J) go borer (winter form) to ...6 PROLEG ~ETS

Figure E. Figure K,. Figure H. Fibure B.

Figure I. Figure C.

Figures A, B, C, H, I, J, L, M, P, R, U, and W, G. L. Hedburg, illustrator, National Animal Disease Center, USDA-ARS, Ames, Iowa; figures D, K,, K,, Q, T, V, and X, Dr. R. G. Weber, entomologist, Department of Entomology and Applied Ecology, University of Delaware, Newark, Del.; figures G, N, 0, and T, Dr. G. L. Godfrey, associate professor, figure E, Dr. D. E. Kuhlman, professor, figure F, W. D. Zehr, photographer and figure S, C. MacMonegle, assistant scientist, all of the Illinois Natural History Survey, University of Illinois, Champaign, Ill.; figure Y, Dr. T. 0. Holtzer, associate professor, Department of Entomology, University of Nebraska, Lincoln, Neb. 6. Tip of chevron mark ( A ) on head 8. Distinct white or pale yellow, 10. Black bar on side of head 11. Head orange-brown, lacking 12. Cutting edge of mandible 13. Head with contrasting white to usually reaching cervical notch middorsal dots on anterior ab- (figure R); body purple or lav- black side bar; patches on back smooth or with 2 medial teeth cream, frontal chevron mark (figure L) . . . subterranean cut- dominal segments (figure 0). . . ender with white longitudinal and sides of body appear to (figure U); larva as in figure V . . . (figure M); distinct hairs on back worms (black, claybacked, dingy, variegated cutworm lines (figure S) . . . stalk borer form pale lavender band across armyworm of body arise from dark tubercles sandhill) - No distinct middorsal dots on - Head and body not marked as the back of each segment - Cutting edge of mandible with (figure X) . . . fall armyworm - Tip of chevron mark ( /\ ) on head abdominal segments go to . . . 9 above go to.. . 11 (figure T); feed on plant roots more than 2 teeth (figure W) go - Head lacking contrasting white, usually not reaching cervical and plant crowns . . . hop vine to. . . 13 frontal chevron mark; hairs and notch (figure M) go to . . . 7 borer tubercles on body inconspicuous Figure 0. Figure R. - Head and body not marked as (figure Y) . . . western bean above; feed on other plant Figure u. cutworm Figure L. partsgoto.. . 12

Figure M.

9. Body covered with spinules (figure P) visible at 10 power, body surface mat-like (figure Q) . . . corn earworm - Body not covered with spinules, appearing smooth or glossy go to. . . 10 7. Body gray or black, marked with distinct yellow stripes along each side of back (figure N) . . . yellow- Figure P. striped armyworm Figure W. - No distinct yellow stripes along sides of back go to . . . 8 CUTTlNG EDGE

Figure N.

STATE LIBRARY OF IOWA DES MOINES, IOWA 50319 Life Cycle and populations with most individual in- more generations are completed by started after January 1 of each year Table 2. Predictions of selected European corn borer activity based on degree-day whenever 50°F (10°C) occurred. accumulation following initial capture of spring moths (minimum developmental Generational Ecotypes sects having similar environmental members of the southern ecotype threshol&50°F [lO°C]), begin degree-day accumulatio~firstsignificant moth flight). During its lifetime, the ECB goes tolerances): northern (one generation before diapause begins. However, because of population di- through four stages of development per year), central (two generations versity and environmental factors, Degreedays ("F) from event Stage Activity (figure 2): egg, larva (borer), pupa per year), and southern (three or The species passes the winter as these degree-day predictions have (transition stage), and moth. The more generations per year). full-grown larvae (figure 2) in corn- not been accurate. Recently, re- First generation stalks, corn cobs, weed stems, or searchers began the degree-day 0 Spring moth flighti succession of these four stages 100 Peak egg hatch constitutes a generation. The larva Beginning midsummer to autumn, spun up in other cornfield debris. accumulations with the capture of the first spring moth in either syn- 200 + 1st-2nd instar Leaf feeding goes through five stadia of growth daylengths shorten and tem- Surviving, or overwintering, ECB be- 350 + 3rd instar Stalk boring (first through fifth instar). During the peratures begin to cool. These come active in April or May in the thetic pheromone traps or light traps. 400 + 4th instar Stalk boring fifth instar, all individuals either pre- environmental changes trigger one central Corn Belt and begin develop- Predictions of subsequent borer ac- 550 + 5th instar Stalk boring ment as outlined in figure 2. tivity based on degree-day accumu- 900+ Pupation pare to pupate and become adults or more genes sex-linked to the 1150-1 700 Adult moths Egg laying (moths) or enter diapause. Diapause male that allow the larval portion of lation following spring flight have is a physiological condition ex- the population to go into diapause, Spring development of the Europear been relatively successful. Table 2 Second generation 1260 Peak egg hatch pressed as suspended development thus preparing the population for corn borer begins when tem- presents the accumulated degree- days using 50°F (10°C) as the 1350 + 1st instar Sheath feeding that is governed by daylength, tem- survival during the cold winter. The peratures exceed 50°F (10°C). 1500+ 2nd instar Sheath feeding perature, and genetic composition of more heat-sensitive ECB populations During the 1950% researchers be- threshold temperature after the initial 1600 + 3rd instar Sheath feeding a population. Based on diapause, of the southern portions of North gan predicting the biological events capture of a spring European corn 1650 (initial stalk boring) the borer populations of North Amer- America are less affected by shorter of ECB by using accumulated tem- borer moth. 'Initiate degree-day accumulation when extended corn leaf height is 17 inches (43 cm) or greater. ica have been partitioned into three daylengths and cooler temperatures perature units called degree-day ecotypes (an ecotype is a group of than their northern counterparts; so, Accumulations were arbitrarily Degree-days are the number of de- grees above the threshold tempera- Once in one of these action sites, Figure 3. European corn borer moths: male, ture occurring each 24-hour period. the female moths drink rain or dew left; female, right. Figure 2. Typical life history of European corn bc )rer in the Corn Belt of the United States. A simple way of calculating degree- droplets and begin emitting a sex days follows. attractant (pheromone) composed of June Jul- I August September Octobe- two isomers of 11 -tetradecenyl ace- I 1 I I 1. (Maximum temperature + tate. This activity usually begins by minimum temperature) divided by 2 10 p.m. and peaks at 1 a.m. The = mean temperature combination of the habitat's micro- 2. Mean temperature - threshold climate and the emission of phero- temperature (50°F or 10°C) = daily mone draws large aggregations of deg ree-days European corn borer moths into I 3. Sum of daily degree-days = relatively small areas of dense accumulated degree-days. vegetation.

Blacklight traps placed in the field Female moths normally mate when before spring moth emergence dur- 48 hours old, then leave the action

ing late April (Missouri) to early June sites to deposit eggs in the target . I (Wisconsin) should capture moths crops. On warm, calm evenings, shortly after they begin to emerge. these egg-laying activities will begin The moths (figure 3) will leave the shortly after sundown and cease by emergence sites in cornfield debris midnight. The females will leave the and fly to patches or strips of dense target crop and return to action sites vegetation, usually grasses, in con- to feed, rest, possibly remate (less servation lanes or near fencerows. than 5 percent), and to await another The vegetation in these habitats suitable evening for egg laying. collects rain droplets and retains dew droplets more effectively than do the leaves of corn plants, so the proper microclimate exists for feed- ing, resting, and mating. If the target crop is corn, females of If the corn is small, less than 16-inch The moths that emerge in midsum- second-generation (third flight) tions, especially if damage begins caused primarily by two species of the spring flight are attracted to the (40-centimeter) extended leaf height, mer fly to dense vegetation, primarily moths will deposit eggs that produce just before the tassel emerges (see fungi, Fusarium moniliforme (Sheld) tallest fields. Egg masses consist of when the eggs hatch, most of the foxtail grass in the Corn Belt, to feed, a third generation. These eggs will Economic Injury Levels). and Gibberella zene (Schw.). Corn 15 to 30 white eggs (figure 4), small larvae fail to become estab- rest, and mate. These mated be laid on tasseled corn plants when yield losses from this disease aver- overlapping like fish scales, and are lished because they wander off and females prefer succulent, recently the kernels of the ears have not Damage results from: age 4 to 5 percent per rotted inter- normally deposited near the midrib die. In many corn hybrids, a primary tasseled corn plants on which to matured beyond the milk stage. node. Only one ECB egg mass per on the underside of corn leaves. Egg factor for this behavioral response is deposit eggs that will produce the These ECB (second or third genera- 1. Leaf feeding (from the first plant, however, can increase the masses are flat and approximately a plant aglucone, 2-4 dihydroxy-7- second generation of European corn tion) will attain the last larval stage generation); numbers of rotted internodes by an l/4 inch (6 millimeters) in diameter. methoxy-1 , 4-benzoxazin-3-one (DI- borer. If corn plants in commercial (figure 7), diapause, and spend the average of four per plant. This Eggs about to hatch have distinct MBOA). The concentrations of vegetable areas have progressed winter. 2. Stalk tunneling (from the first and increase in stalk rot is directly related black centers. This is the black head DIMBOA in a given corn hybrid beyond the silking and tasseling second generation); to boring into stalks and ear shanks of the larva visible through the usually decrease proportionally with stage, the moths will lay eggs on How Corn Is Damaged by ECB larvae. Losses will increase translucent egg shell. The eggs plant growth. A greater proportion of pepper plants or other economically by the European Corn Borer 3. Leaf sheath and collar feeding the longer the corn harvest is hatch (figure 5) in 3 to 7 days, larvae survive on corn in mid-to-late important hosts. Bear in mind that yield losses from (from the second and third genera- delayed. depending on weather conditions. whorl stage, 22- to 36-inch (55- to both first- and second-generation tion); and Each mated female is capable of 80-centimeter) extended leaf height. During the silking and tasseling borers are primarily because of Damage because of direct feeding depositing an average of two egg Usually corn plants are mid-to-late- stage of corn growth, 90 percent of physiological losses rather than ear 4. Ear damage (from the second and by ECB on the kernels of the ear in masses per night for 10 nights. The whorl when most of the eggs are the egg masses will be laid on the droppage. The corn plants fail to third generation). inbred seed cornfields can be signif- majority of the masses, however, will deposited during the spring borer undersides of the three leaves above yield well as a result of corn borer icant. This type of feeding on sweet be deposited during the first 6 flight. But, even in the presence of the ear, on the ear husk, on the damage. Hybrids with resistance to European corn borer damage results corn is especially important to can- nights after mating. optimal corn plant stage, tem- undersides of the ear leaf, and the the first generation (leaf-feeding re- in poor ear development, broken ners and market gardeners (see perature-related climatic variables, three leaves below the ear. During sistance) can reduce the amount of stalks, and dropped ears. The major- Sweet Corn). such as moisture stress and evap- this time of year, depending on loss; but, to date, these hybrids do ity of the yield loss is because of the Figure 4. European corn borer egg masses on oration, will kill 22 to 68 percent of weather conditions, the eggs will not have the yield potential of more inability of the plants to produce as Components of Management underside of a corn leaf, the freshly hatched larvae. Those hatch in 3 to 5 days. About 75 susceptible hybrids. Full-season a result of damage. With persistent Reaching the proper management that live move to the whorl to feed percent of the small larvae will move hybrids tend to be more susceptible autumn winds and dry weather, how- decision is dependent on many and develop. Eventually, they burrow to the leaf axils and the remaining 25 to the second-generation and third- ever, tunneling in the stalks and ear bidogical and economic factors. into the stalk of the corn plant where percent to the ear to feed on sheath generation borer; but, they typically shanks increases stalk breakage and The following simple management they change to pupae during the and collar tissue, or on pollen col- have a greater yield potential that dropped ears, respectively. Recent model is effective. More complex summer (figure 6). lected in these sites. Late in compensates for the increased sus- research has shown there is close microcomputer-based management summer, particularly in the southern ceptibility. Yield losses during all association between second- and models are available from Kansas portions of the north central region, stages of corn development can be third-generation ECB infestation and State or Pennsylvania State extremely high during severe infesta- incidence of stalk rot. The disease is Universities.

Figure 6. European corn borer pupa in a turgid cornstalk. Researchers from several states, co- I Figure 7. Fifth-stage European corn borer larva. Ready to spin silk and go into diapause. operating and coordinating their investigations through NC-180, are ,rapidly accumulating the data nec- essary to localize the European corn borer management model. Presently, research is under way to validate the latest ECB management model across the north central region of the United States and in member states outside the region. For more informa- tion, acquire a copy of Volume 1, Number 1, of the NCCl Software Journal; or, contact a representative of the NC-180, Technical Committee on Stalk-boring Insects (listed on inside front cover). Scouting Techniques conditions (temperatures and of survival expressed in cavities per showing an intermediate level of count for differences in yield loss mated as a symmetric 20-day tri- Scouting is recommended to assess moisture) and the resistance of the plant using a susceptible hybrid resistance (A619 X H632 and A632 caused by leaf axil feeding (figure 9) angle, the entire egg-laying period field populations of pests. The key to plant. Table 3 shows a comparison (B73 X Mo17) and two hybrids X H99). Plants were manually in- and subsequent stalk boring. This can be determined by locating initia- good scouting is representative sam- fested with first-instar ECB larvae at information will result in more eco- tion of egg laying. pling. Where possible, five random three different plant heights achieved nomically accurate decisions. samples of 20 consecutive plants Table 3. Mean numbers of cavitieslplant in 3 varieties of corn at different plant heights by planting corn at 2-week intervals Research in Kansas and discussions lnitiation of egg laying can be deter- should be examined for every 40 to 35 days following manual infestation (June 21) of ca. 60 European corn borer la~el with specialists in other states indi- mined by observing the date when plant. (Concord, Nebraska, 1980 J. F. Witkowski). in May. 50 acres (16.2 to 20.2 hectares). cated that egg laying takes place first moths are collected in a nearby Extended Number Cavities Althouah" less ~recise.as a ~ractical Scouting for first generation should over a 20-day period, with peak egg blacklight trap. When a blacklight compromise fir very large fields, 80 H*dd, Planting leaf whorl of per trap is not available, frequent egg date ht. (in.) ht. (in.) leaves plant2 begin when plants with extended deposition 10 days after the first acres (32.4 hectares) or more, leaves are 17 inches (43 cen- eggs are deposited (figure 1Oa). If mass sampling (2 to 3 days apart) is growers and consultants may have to B73 Mo17 May 1 65 46 12 3.0 a3 timeters). This normally occurs in the egg-laying period is approxi- necessary. When no other informa- limit their surveys to five or more A619 x A632 64 49 12 1.6 b A619 x H99 67 67 12 1.4 b middle May in southern Illinois, random sam~lesof 25 consecutive Kansas, Kentucky, and Missouri, dur- May 15 plants per field. As sampling inten- ing early June in Delaware, Iowa, Figure 10a. The proportion of the total egg complement deposited by the time the sample was sity decreases, the chances of northern Illinois, Indiana, Maryland, taken 8 days after oviposition began. making a wrong decision increase Nebraska, and Ohio, and mid-June Peak greatly. Considering the cost of con- 873 x Mo17 May 30 17 11 6 1.3 a A619 x A632 19 10 6 1.0 a in central Wisconsin, central trol strategies, if there is any doubt A619 x H99 19 12 6 0.9 a Michigan, southern Minnesota, as to the seriousness of the infesta- '873 x Mo17 = Susceptible southern Ontario, Pennsylvania, and tion, more samples should be taken. A619 x A632 = lntermediate resistance South Dakota. The moths become A619 x H99 = lntermediate resistance 2Each mean made up of 80 observations (10 plants split per replication x 8 replications). active in late June to early July in To eliminate the edge effect, the first Weans followed by a common letter are not significantly different at the 0.05 level of probability. Alberta, Manitoba, northern sample should be taken after walk- Minnesota, Quebec, and North Prnnnrtinn ing 100 feet (30.4 meters) or more Dakota. Consult table 2, which lists into the field. The remaining sample Figure 8. Whorl feeding by European corn degree-day accumulations begin- sites should be taken randomly borer larvae. ning with the appropriate moth across the entire field, using care to capture during the spring of the year. @ 10 consider all representative topo- Days After Initiation of Egg Laying graphical, environmental, and Treatment guidelines for second- or cultural features that may influence third-generation European corn borer plant height, plant maturity, and in most states have been based on Figure lob. Key dates that must be established with reasonable certainty to evaluate the plant density. If more than one 35 to 50 percent of the plants in the seriousness of European corn borer infestations in field corn. variety is planted in the same field, pre- to post-tasseling stage of corn consider each variety as a separate development having an egg mass. Sample Here to Establish field for scouting purposes. the Magnitude of the Based on model simulations, per- Population (Height=Egg sonnel in Kansas have lowered the Treatment guidelines for first- threshold to 10 to 20 egg masses Sensity) generation ECB are based on whorl per 100 plants. The problem with feeding (figure 8). Examine plants for using a standard economic injury fresh whorl feeding and record the level for ECB across the entire number of plants damaged. If the geographic range is that the syn- margins of the damaged area are chrony of insect and plant brown to black, then the damage is development differs between regions old. Dissect two infested plants per and fields. Larvae that initiate feed- sample of 20 or 25 plants and look ing earlier in a plant's development for live borers. It is important to have a greater potential to cause check for live larvae because borer yield reduction than those initiating mortality in the first 3 to 5 days feeding nearer to physiological ma- following hatch is normally very high. turity of the corn plant. Plant Major causes of mortality in the developmental stage during ECB whorl are adverse environmental egg laying must be known to ac- Days After lnitiation of Egg Laying tion is available, begin sampling input into the ECB management mowed waterways extending through value of actual or potential damage One of the greatest values of the EIL ceed three per plant, however, the when the most advanced cornfield in model. For instance, if six egg the field. These action sites of dense equals the cost of preventing the and ET concepts is in monitoring the actual loss caused by each addi- the area has reached the pretassel masses per 100 plants are detected vegetation are necessary "stopping damage (table 4). The economic build-ups of potentially damaging tional larva will not be linear. Control stage. 9 days after egg laying begins, we off" points for female moths before threshold (ET) is the population den- pest populations and reaching a measures for ECB vary across the estimate that 40.5 percent of the egg deposition begins in the corn- sity at which control measures control or management decision be- species distribution, but for suppres- Researchers believe that locating an eggs have already been laid. A final field. Research using a I-meter bar should be initiated to prevent the fore economically important grain sion of ECB during the whorl stage egg mass is unlikely before 5 per- density of 0.69 larva per plant will brushed through the grass canopy pest density from surpassing the yield reductions occur. The ET for of corn growth granular formulations cent of the eggs have been deposit- develop if insecticides are not used. for 10 meters at several places EIL. first generation ECB in the Corn Belt usually outperform liquids, 80 to 50 ed in the field. Based on the 20-day around field edges, in waterways, has been well researched. As a percent, respectively. The proportion symmetric egg-laying period, initia- Egg mass densities also can be and between rows of weedy fields To apply EIL and ET to the European general rule during whorl stage corn of ECB population killed (PC) used tion of egg laying would occur 3 approximated by monitoring moth has shown that the number of moths corn borer, the concept of a treat- growth, there is a 5 percent yield in the formula for the EIL presented days before detection of the first egg activity in action sites. Walking flushed per 10 meters correlates with ment "window" must be introduced reduction for each of the first three in table 4 is an average (0.67) masses if regular intensive sampling through an action site will cause the number of egg masses depos- and understood. Only larvae that larvae (table 4) that bore into the developed from these percentages. has been conducted at 2-day inter- moths to flush. This adult flushing ited on the corn plant (figure 11). have not bored into the plant can be stalk. When numbers of larvae ex- vals. For example, if the first egg technique is a useful way to deter- killed. Consequently, there is a spe- mass was observed on July 4, then mine whether scouting for egg Economic Injury Levels, cific time period, or "window," during egg laying probably was initiated on masses should be initiated. Moths Economic Thresholds, and which pesticides must be applied if Table 4. Corn loss caused by European corn borer and calculated economic injury July 1. Timely sampling will reduce may be seen during the early morn- Reaching a Management Decision they are to be effective. Egg deposi- level (Ell) for various corn growth stages (R. A. Higgins, R. E. Lynch, and discrepancies between adult flight ing by disturbing grassy field The economic injury level (EIL) is the tion in a given field may last 3 F. L. Poston). Calculated EIL1 and egg deposition in nearby fields. margins, weedy fencerows, and un- pest population density at which the weeks. Available insecticides kill lar- Loss bu./A % loss vae over a relatively short period of Plant stage (ECBIplant) (ECBIplant) 1 application 2 applications Once the initiation of egg laying has time; therefore, they must be appiied Early whorl 7.7 5.5 1.45 2.90 been established, an additional egg Figure 11. Predicted number of European corn borer egg masses per corn plant, based on before all eggs are deposited. If the Late whorl 6.2 4.4 ' 1.81 3.62 mass sample should be taken 8 to number of European corn borer moths per 10 meters of dense grass (M. E. Derrick and W. B. treatment is delayed, larvae from Pretassel 9.2 6.6 1.21 2.41 10 days after the initiation of egg Showers). eggs deposited early in the egg- Pollen shedding 6.2 4.4 1.81 3.62 laying to determine the density of the laying (oviposition) period will suc- Kernels initiated 4.2 3.0 2.65 5.31 egg population (figure lob). Sam- ceed in entering the plant. The CC * 'EIL = pling at this time minimizes sampling decision to treat, therefore, should be PL x MV x EY x PC errors caused by low egg mass based on an estimate of the poten- densities and allows time to instigate tial European corn borer population Cost of control (CC) = $16.00/A, 1 application; CC = $32.00/A, 2 applications. Pmportion of yield lost per ECB (PL) = based on percentage loss per plant stage (column three). Market value (MV) = $2.001bu. a control procedure if needed. To density expected to establish within Expected yield (EY) = 150 bu./A. Pmportion of ECB population killed (PC) = 0.67. determine the egg mass population, the stalks. the sample should be taken at random. For a single application, an insec- Table 5. EIL table. ticide should be applied from 10 to % of 100 (125) plants infested x average number Research indicates that about 91 14 days after initiation of egg laying, larvae per infested plant = larvae per plant (from checking whorls of percent of the total egg mass com- which would be 0 to 4 days after the 2 plants from each sample site) plement on 25 consecutive plants at peak. Two applications are frequently * four locations within a field can be required for suppression of second larvae per plant x 5% loss per larva = % yield loss accounted for on the middle seven or third generation populations be- corn leaves (three leaves above and cause timing with one application is % yield loss x expected yield (bushels) = below the ear leaf). These seven leaf seldom perfect. If two applications bushels per acre loss samples can be corrected to whole are used, then the first should be price per bushel = plant samples without loss in the bushels per acre loss x $ applied at 25 to 30 percent comple- $ loss per acre accuracy of the control decision. An tion of egg laying and the second estimated whole plant count can be about 7 days later (see Timing $ loss per acre x 67% control (from table 4) = $ calculated by multiplying the total Insecticide Treatment, table 7). Note preventable loss per acre number of egg masses found on the re-entry restrictions on some seven leaf count by 100 and dividing pesticide labels that would preclude $ preventable loss per A - $ cost of control per -0.2 I acre = $ benefit or loss from treatment by 91. The resulting full plant egg ; I I I I I I I I I rescouting the field without adequate mass density estimate per 100 0 10 20 30 40 50 60 70 80 90 100 protective equipment. plants serves as the egg population Number of Adults in Grass A relatively precise decision-making where: EM = The average number of egg The formulae for estimating PO are Incorrectly defining the oviposition For example, a field of corn is guide for control of ECB during NA = Number of insecticide ap- masses per plant, based on the given so they can easily be pro- distribution through time has the shedding pollen when the majority of whorl stage corn now is being used plications latest scouting reports. Count both grammed on a microcomputer. following effects: shortening the egg masses are deposited. The in much of the Corn Belt. To deter- AC = Application cost (dollars per hatched and unhatched egg masses oviposition period from 20 days anticipated yield without European mine the need for treatment after acre) (egg masses per plant). Case 1: If the sample dat$ is later greatly alters the predicted PPD, corn borer damage is 150 bushels scouting for damaged plants and IC = Insecticide cost per applica- PO = The proportion of the total egg than or equal to the termihation of lengthening the oviposition period per acre. Corn has an anticipated live larvae, the following must be tion (dollars per acre) -complement deposited by the time oviposition then PO = 1.d. beyond 20 days has only a slight market value of $2.50 per bushel considered: the cost of treatment, the sample egg mass collection effect on the PPD and accuracy of and the total control cost for one expected yield per acre (hectare), The benefit (B) derived from a (EM) was taken. Case 2: If the egg mass $ample the final control decision. application is $12.50 per acre. The value of the grain, percentage con- control action is calculated as date (for density estimation) is earlier application is expected to kill 67 trol achieved, potential yield loss, follows. Correct estimation of PO is essential than, or equal, to the peak in The same variables used to calcu- percent of the larvae (PC = 0.67). and pest population. These data to accurately predict the PPD of the oviposition and after initiation of late the cost per benefit ratio can be may be used by calculating an EIL B = PC x PL x MV x EY x PPD ECB. This is necessary to arrive at oviposition, then PO = x2/a(a+b). used to calculate the EIL for any set Thus, table (table 5). the proper management decision. To of economic and biological condi- where: calculate PO, the shape and length Case 3: If the egg mass sample tions. The EIL is calculated using the EIL = Treatment guidelines for second- PC = Proportion of the ECB popula- of the ECB egg-laying period must date (for density estimation) is later following equation. and third-generation European corn tion killed by the insecticide (PC = be estimated as described in the than the peak of oviposition but borer are frequently made when a 1.0 if 100 percent are killed; PC = scouting section (see also the win- before the termination of oviposition, predetermined percentage of plants .80 if 80 percent are killed, etc.) dow for second-flight moths, table then PO = 1 - (a + b - x)'/b(a + b). $12.50 per acre EIL = in the pre- and post-tasseling stage PL = Proportion of yield lost per 2). Assuming that the values pre- $11.05 per acre

All variables are defined-- as- for~ the of corn development are infested borer per plant (table 4) (propor- sented above for eggs per mass, where: with egg masses. Computer software tional loss per borer per plant) and length and shape of the oviposi- x = (Sample date) - (initiation of Per benefit presented EIL = 1.13 borers per plant at earlier. The EIL is the PPD value for a dynamic decision model for MV = Anticipated corn market value tion period are reasonable, PO for oviposition date) when the cost per benefit ratio season's end. second generation European corn in dollars per bushel (dollars per bu) any sample date during the oviposi- a = Days from initiation of oviposi- borer has recently been developed. EY = Expected corn yield in bush- tion period can be calculated. Table tion to peak of oviposition equals 1. Using the same factors that govern els per acre (bushels per acre) 6 is a compilation of estimated PPDs b = Days from peak to termination calculation of the EIL, both the cost without ECB infestation using these assumptions. Columns of oviposition. (dollars per acre) of each insecticide PPD = Predicted potential ECB represent the number of days into application and the benefit (dollars population density (ECB per plant) the oviposition period that the most per acre) derived from the control recent egg mass sample was taken. Table 6. Predicted potential population densities of ECB larvae for various egg mass densities per whole corn plant (or corrected action are calculated and compared For the second generation, the fol- egg mass densities if 7-leaf count used1) collected on different dates during the oviposition period. Column one depicts the average - to assess the value of insecticide lowing equation is used to calculate number of egg masses per plant Days after initiation of egg laying and proportion of egg laying complete (in parentheses) application. Thus, a comparison of the potential population density counted in the sample. Each cell in Number of egg 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 dollars spent for larval suppression (PPD) per plant. table 6 is the calculated PPD for a massesiplant (0.125) (0.180) (0.245) (0.320) (0.405) (0.500) (0.595) (0.680) (0.755) (0.820) (0.875) (0.920) (0.955) (0.980) (0.995) (1.00) (cost) and dollars gained by initiat- given observed density of egg SV x EPM x EM 0.02 0.72 0.50 0.37 0.28 0.22 0.18 0.15 0.13 0.12 0.11 0.10 0.10 0.09 0.09 0.09 0.09 ing control measures (benefit) can PPD = masses per plant and sample date. PO 0.04 1.44 1.00 0.74 0.56 0.44 0.36 0.30 0.26 0.24 0.22 0.21 0.20 0.19 0.18 0.18 0.18 be used to formulate management For example, if eight egg masses 0.06 2.24 1.56 1.14 0.88 0.69 0.56 0.47 0.41 0.37 0.34 0.32 0.30 0.29 0.29 0.28 0.28 decisions. Using the model, egg per 100 corn plants (egg mass 0.08 2.96 2.06 1.51 1.16 0.91 0.74 0.62 0.54 0.49 0.45 4.42 0.40 0.39 0.38 0.37 0.37 where: population density is predicted be- density = 0.08/plant) were counted 0.10 3.68 2.56 1.88 1.44 1.14 0.92 0.77 0.68 0.61 0.56 0.53 0.50 0.48 0.47 0.46 0.46 SV = The average proporti~nof 0.12 4.40 3.06 2.24 1.72 1.36 1.10 0.92 0.81 0.73 0.67 fore completion of oviposition and a 8 days into the oviposition period, 0.63 0.60 0.58 0.56 0.55 0.55 individuals surviving to cause 0.14 5.12 3.56 2.61 2.00 1.58 1.28 1.08 0.94 0.85 0.78 0.73 0.70 0.67 0.55 0.64 0.64 timely control decision is made using the predicted PPD would be 1.16 damage. If no other information is 0.16 5.92 4.11 3.02 2.31 1.83 1.48 1.24 1.09 0.98 0.90 0.85 0.80 0.77 0.76 0.74 0.74 a straightforward costtbenefit larvae per plant. The recommended 0.18 6.64 4.61 3.39 1.66 available, based on studiebap 2.59 2.05 1.40 1.22 1.10 1.01 0.95 0.90 0.87 0.85 0.83 0.83 analysis. sampling date of egg masses to 0.20 7.36 5.11 3.76 2.88 2.27 1.84 1.55 1.35 1.22 1.12 1.05 1.00 0.96 0.94 0.92 0.92 ducted in Kansas and Iowa, a value estimate PPD is from 8 to 10 days 0.22 8.08 5.61 4.12 3.16 2.49 2.02 1.70 1.49 1.34 1.22 1.10 1.10 1.06 1.03 1.02 1.01 of 0.2 is recommended. Environmen- 0.24 8.80 6.11 4.49 3.44 2.72 2.20 1.85 1.62 Control Costs (CC) are calculated after initiation of egg laying (table 6). 1.46 1.34 1.26 1.20 1.15 1.12 1.11 1.10 0.26 9.60 6.67 4.90 3.75 2.96 2.40 2.02 1.76 1.59 1.46 1.37 1.30 1.26 1.22 1.21 1.20 using the following equation. tal conditions may warrant research This allows the user to optimize in other regions to establish more 0.28 10.32 7.12 5.27 4.03 3.19 2.58 2.17 1.90 1.71 1.57 1.47 1.40 1.35 1.32 1.39 1.29 sampling precision and if needed, 0.30 11.04 7.67 5.63 4.31 3.41 2.76 2.32 2.03 appropriate local values. 1.83 1.68 1.58 1.50 1.45 1.41 1.39 1.38 CC = NA X (AC + IC) still leave time for applying insec- 0.50 18.40 12.78 9.39 7.19 5.68 4.60 3.87 3.38 3.05 2.80 2.63 2.50 2.41 2.35 2.31 2.30 EPM = Eggs per mass. If more ticides while larvae are exposed. 0.75 27.60 19.17 14.08 10.78 8.52 6.90 5.80 5.07 4.57 4.21 3.94 3.75 3.61 3.52 3.47 3.45 specific local information is not avail- 1.OO 36.80 25.56 18.78 14.38 11.36 9.20 7.73 6.76 6.09 5.61 5.23 5.00 4.82 4.69 4.62 4.60 able, suggested value is 23 (eggs 1.25 46.00 31.94 23.47 17.97 14.20 11.50 9.66 8.46 7.62 7.01 6.57 6.25 6.02 5.87 5.78 5.75 per egg mass). 1.50 55.20 38.33 28.16 21.56 17.04 13.80 11.60 10.15 9.14 8.41 7.89 7.50 7.46 7.23 6.93 6.90 7-leaf count 'Whole plant count = x 100 91 Figures 12a through 12e illustrate the alent, critical egg mass density that damaged. Early-planted corn, how- Figure 12a-e. Calculated Economic Injury Level (EIL or PPD) values when control cost, crop value, and corn stage during egg deposition are effect of control cost, crop value should cause the user immediate ever, escaped the second gener- varied. (MV x EY), and corn stage when concern can now be determined. For ation because the plants were no Early Whorl Kernels Initiated eggs are deposited (PL) on the EIL instance, if sampling to establish the longer attractive for egg laying. But, (expressed as a PPD). Percentage current egg mass density did not late-planted corn was highly attrac- control (PC) is assumed to be 67 occur until 10 days after oviposition tive for egg laying and these percent. If percentage control is started (approximately the peak in plantings sustained large numbers believed to differ from 67 percent, egg laying), then somewhere be- of second generation ECB. the alternative value can be sub- tween 0.12 and 0.14 egg masses stituted in the EIL formula. EIL values (hatched and unhatched) per plant Currently, there is a trend to plant can be easily determined using the (12 to 14 per 100 plants) would be long-season corn with heavy fertiliza- figures, if the 67 percent control is the ET. Eight days after initiation of tion. When planted early, this corn acceptable. Select the figure for the oviposition (2 days before the peak can be attacked by the first genera- corn growth stage when the majority in egg laying) 32 percent of the tion and may still be attractive to the 0 0 of egg deposition is noticed. Next, eggs have been laid. At that time, an second generation. This is particu- 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 determine the crop value by multiply- average of one egg mass on 8 larly true in those areas of the Corn Crop Value ($/Acre) Crop Value ($/Acre) ing the expected yield (bushels per percent of the plants is potentially Belt where irrigation is available and acre) by the anticipated market economic (table 6). If we sample 5 used throughout the growing season. value (dollars per bushel). Locate days into the egg-laying period only The corn hybrids planted in these Late Whorl and Pollen Shedding Dough the calculated crop value on the 12.5 percent of the eggs have areas are usually long-season, horizontal axis of the figure. Now probably been laid and about three planted very early, and planted at a follow a straight line vertically up the egg masses per 100 plants would be higher population than their neigh- figure until the appropriate control enough to indiciate that economic boring nonirrigated cornfields. cost curve is intersected. Move hori- problems are very likely without well zontally to the vertical axis. The PPD timed insecticide treatments. Sam- In some areas of the Corn Belt, value where the axis is intersected pling early in the oviposition period, reduced tillage practices are being represents the calculated EIL value. however, greatly increases the used in corn production. Most re- chance of reaching an improper duced tillage systems, especially Because a control action must be decision. those that do not include plowing, permit increased survival of the over- 0 0 taken when eggs are present, it is 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 wintering population of borers. more useful to express the EIL in Both of the approaches described Crop Value ($/Acre) Crop Value ($/Acre) terms of egg masses per plant that above (cost per benefit and EIL) Proper weather during the spring will result in an economic larval assume that the damage inflicted is increases the probability of subse- largely restricted to borers entering quent attack by the first generation. density at season's end. By convert- Pretassel Figure 12f. Oviposition and subsequent damage over three stages of ing back to egg masses per plant, the stalk over one plant growth corn development. . the user would have time to respond stage. Figure 12f shows that this is If weather favors survival of the borer before larvae bore into the plant and an oversimplification. More refined when long-season corn is grown, it become protected from the action of computer-based models that ac- may be necessary to treat the field contact insecticides. Therefore, un- count for the correlation between for more than one generation. When der these assumptions, the number oviposition, phenology of stalk entry light traps show heavy moth flight Development of egg masses per plant that result by the surviving larvae, plant devel- and the corn is shedding pollen, in the EIL is the ET. opment, and grain yield Iws green silks are present, or the ear is vulnerability are under devglbment. in the milk stage (table 4), treatment Using the information from the exam- may be needed to control the sec- Stage ple above, refer again to table 6. liming Insecticide Treatment ond or third generation. Within the body of the table, locate Previously in the Corn Belt, early- 100 200 300 400 500 600 700 800 0 4 12 20 all the values in each ,column that planted corn was most attractive to Timing is one of the most critical Crop Value ($/Acre) Days After Initiation of Egg Laying are closest to 1.13. Because PPD moths that produced first-generation aspects of European corn borer and the number of live borers per European corn borers. These plant- control with insecticides. The plant at the season's end are equiv- ing~were frequently severely number and timing of whorl-stage equipment availability and the time Resistant Varieties Germ plasm resistant to sheath- treatments depend upon the severity ear tip and collar area of field corn When high-clearance equipment is required to complete application Selections of inbred dent corn lines collar feeding by second- or third- of the infestation and the degree of cannot be controlled by an insec- available, it can be modified to apply over large acreages often necessi- resistant to leaf feeding by first- generation borer has been difficult to control desired. Except under very ticide application (see Sweet Corn). either granules or liquids. To control tate the use of aerial equipment. generation borers have been made locate. There has been, however, a heavy infestation, one treatment is leaf feeding, granules need to be during the past six decades. Today considerable decrease in sheath- usually sufficient on field corn during Application Equipment directed into the whorl of the plant. In those areas where insecticides are most seed corn companies have collar feeding on inbred lines and the whorl stage of corn development. Most applications for control of To control sheath-collar feeding dur- commonly applied at planting or hybrids available with intermediate hybrids grown during the 1970s, Seed corn or other extra-value crops European corn borer are aerially ing the pre- and post-tassel stages cultivation for control of rootworm resistance to leaf feeding (figure 13). compared with genotypes grown may profitably receive two or more applied. In those areas with a history of corn development, granules need larvae, application of a systemic It was estimated that 21 million acres during the 1930s. Although most treatments. of European corn borer problems, to be directed over the entire plant of corn in 1969 were planted to hybrids grown today are susceptible granules are the preferred formula- and into leaf axils. This is usually insecticide seemingly controls whorl- feeding European corn borer. ECB hybrids whose pedigree contained to sheath-collar feeding (figure 14), Various procedures are available to tion, particularly for control during accomplished by using 7 to 10 inch control with this method, however, at least one inbred line with an they vary in degree of susceptibility. determine the time of application for the whorl stage of corn development. (18 to 25 centimeter) spreader band- has been inconsistent and therefore intermediate degree of resistance. Progress also has been made during control on whorl stage corn. These Fortunately, most aerial operators are ers attached to delivery tubes it is not recommended. the past 45 years in developing procedures include tassel-to-bud usually equipped to apply either a extending from each insecticide box. Since the mid-1970s, however, the hybrids with better root systems, ratio, a certain percentage moth granule or a liquid formulation. Al- The application of insecticides via acreage planted to hybrids resistant stalk strength, and ear shank emergence, accumulated egg though not true for all compounds, For liquid applications to reduce leaf injection into irrigation water (insec- to leaf feeding has decreased dra- strength. Hybrids are available today masses per 100 plants, and percent- efficacy comparisons between gran- feeding, use one or two nozzles per tigation), particularly with overhead matically. This is because the inbred with some tolerance to late summer age whorl feeding. Percentage fresh ules and liquids of the same row. Adjust the nozzles to deliver the center pivot irrigation systems, is an line 873, large yielding but suscepti- borer attack. These hybrids stand whorl feeding and the presence of compound applied over whorl stage spray above and into the whorl. To effective method and is rapidly be- ble to leaf feeding, has become well and retain ears despite heavy live larvae in the whorl have proven corn usually favor the granules. control sheath-collar and ear feed- coming common in some irrigated widely used in hybrid combinations. infestation. to be the best criteria for treatment Granules have additional advan- ing, use four nozzles per row and areas of the Corn Belt. Because it is timing. See the previous section for tages: (1) no mixing or water is direct the spray at the ear zone. relatively new, the technology is cost versus benefit in table 5 for needed, (2) there is less drift, Thorough coverage is important. changing rapidly. Federal and state Figure 14. Corn hybrid displaying resistance whorl stage corn. Treatment after the (3) personal hazard is usually less, Ground applications should be ap- legislation governing its use is also to sheath-collar and leaf axil feeding by borers have invaded the stalk will not and (4) there is less hazard to plied with a minimum of 10 gallons European corn borer, left. Susceptible hybrid, changing rapidly. Before using this Figure 13. Corn hybrid displaying resistance be satisfactory. honeybees and other beneficial in- (37.9 liters) of water per acre. To to whorl feeding by European corn borer. with few remaining leaves, right. sects. Liquid insecticides, however, control whorl feeding, these same method of application, consult your 4T local Cooperative Extension Service Intensive scouting is necessary to give better control of ECB moths and granular or liquid delivery systems and the respective regulatory agen- determine the time of application for larvae during the tasseling and silk- can be mounted on a tool bar and cies. Some states have very specific control during the tasseling and ing stage of corn development. Also, used with cultivation layby equip- rules and regulations regarding the silking stage of corn development. liquid formulations are advantageous ment. Generally corn is too tall and injection of chemicals into irrigation Without scouting and development of later in the crop development be- already cultivated when decisions water. an economic threshold (ET) for sus- cause European corn borer may not are made to control whorl feeding. pect fields, control of the second- or be the only target insect pest Although there are distinct advan- One of the primary concerns of third-generation borer is more diffi- species. tages to ground application, insectigation is potential contamina- cult. More than one insecticide tion of underground water. If insecti- application may be necessary. The gation is used, comply with all laws best information to date indicates Table 7. Effectiveness of ground-applied Furadan 10% granules at 1.0 Ib. A.I./A and regulations, including those that the first application should be against second-generation European corn borer in field corn. Variety Acco 2901 promulgated by the Environmental applied over the grassy action sites planted June 6, 1978. (Cedar County, Nebraska, J. F. Witkowski). Protection Agency, the manufacturer (for moth control) and the cornfield Mean borerstplant of the insecticide, and local reg- when eggs begin to hatch and % reduction Treatment timing and date k. Number' ulatory agencies. At a minimum, larvae are visible in leaf axils (table -. 1. At 25% egg hatch (Aug. 14) make sure the well is equipped with 7). Choose an insecticide that will 2. At 25% egg hatch + 4 days a check valve to eliminate the pos- control moths and hatching borers 3. At 50% egg hatch (Aug. 16) sibility of reverse flow, or back over several days. Nonresidual in- 4. At 50% egg hatch + 5 days siphoning, in the event the system secticides are not suitable for control 5. At 75% egg hatch (Aug. 18) 6. loses pressure and shuts down dur- during corn tasseling and silking. If At 75% egg hatch + 5 days 7. At 95% egg hatch (Aug. 21) ing the insecticide application fresh eggs are still observed 7 to 10 8. At 95% egg hatch + 4 days process. The check valve will elimi- days following the first application, 9. No treatment nate the possibility of contamination treat a second time. Borers in the 'Each mean made up of 40 observations (10 plants x 4 replications). 2Mean separation by Duncan's multiple range test; P = 0.05. of the well with the insecticide. In the future, hybrids with resistance eggs than normal moths. This pro- efficacious against whorl feeding days 0 to 2 and 4 to 6 by 1% inches 'egg masses being deposited in that when second-generation borers are to both leaf and sheath-collar feed- tozoan plays a moderate-to- and sheath-collar feeding. This mi- (2.6 centimeters) and % inch (2.2 field. Fields planted extremely early attacking. Early-planted corn that is ing should be available. Several significant role in reducing borer crobial agent is being extensively centimeters) of rainfall, respectively, by an individual grower will also in stage R2 (kernels initiated, table seed corn companies have extensive populations. used through pivot irrigation (insec- caused 87.5 percent mortality by the provide conditions for concentration 4) when the second generation of breeding projects and all companies tigation) to control ECB. It also is sixth day after hatch. Although the of ovipositing female moths with a borer is present has a better chance can use germ plasm resistant to Two additional parasitic protozoa, very attractive because of reduced final survival under both moisture resulting heavy infestation. of avoiding serious loss. European corn borer released by Vairimorpha necatrix and environmental contamination. stress and inundation is similar (day U.S. Department of Agriculture, Agri- Vairimorpha sp., will infect the borer 24), the amount of damage sus- b. Two-generation regions. Early c. Three- and four-generation re- cultural Research Service-State under laboratory conditions. Nuclear polyhedrosis viruses iso- tained by plants from borers planting of resistant hybrids also is gions. The benefits of early planting Experiment Station joint corn breed- V. necatrix is extremely virulent and lated from the alfalfa looper, stressed for moisture could be more considered to be a practical man- remain the same for one- and two- ing projects. This germ plasm can is promising as a microbial control Autographa californica, and a mint severe because of the slower in- agement approach. Extremely early generation regions. In the three- and be used directly in hybrid combina- agent. looper, Rachiplusia ou, will infect the crease in larval mortality. Regardless planting (or earlier than other pro- four-generation regions, however, all tion or as genetic stocks for borer. Recent field experiments sug- of the precautions taken before ducers) will result in heavier-than- planting dates are subjected to a breeding purposes. Beauveria bassiana, a widespread gest viruses might show promise as planting, climatic variables will ulti- average infestation of second- minimum of two generations of fungus, can kill more than 50 per- control agents. It is unlikely, though, mately determine the number of ECB generation borers for that specific borers. Earlier plantings receive in- Biological Agents cent of the overwintering populations that viruses will have a practical (table 8). field if moths are present during the festations from first and second The European corn borer is attacked of the borer in a given year. Conidia application for European corn borer tasseling and silking period. Late generations. Later plantings receive by many natural enemies throughout of B. bassiana remain in the soil and control. Cultural Practices planting also will be attractive to infestations from second and third its life. Lady beetles and other ontin corn plant debris. Epizootics, There are several management prac- concentrations of ovipositing females generations. But, similar to the two- insects and predacious mites feed therefore, occur most readily during Weather tices that may effectively reduce the and will result in above-normal in- generation regions, earlier planting is on the eggs and young larvae. periods of ample rainfall with tem- Changing crop rotation practices severity of local infestations of festations and damage by second- option.a viable and practical management Picnic beetles, which enter the borer peratures in the mid-80s°F (about during the past 20 years (from corn- European corn borer. But, to have generation borers. Except for a few tunnels to feed on plant sap, will 28°C). oats to corn-soybeans) and chang- significant impact some of these tolerant corn hybrids, heavy second- injure borers and crowd them out of ing harvesting methods (from picker management practices must be con- generation infestations in corn 2. Grass-weed and Adult European the tunnels. The downy woodpecker, A group of tiny wasps, Tricho- harvest-ear storage to combined ducted over a community or county- planted early or late will result in Corn Borer Suppression ringneck pheasant, and other birds gramma spp., attacks the eggs of harvest-shelled grain storage) have wide area. broken stalks, dropped ears, and Recent research suggests that dig overwintering borers out of their many lepidopterous insects, includ- dramatically reduced overwintering reduced yields. It must be remem- Euwpean corn borer larval popula- chambers in cornstalks and plant ing European corn borer. In Texas, populations of European corn borer 1. Planting Time bered that at present, resistant corn tions can be kept below economic debris. Parasitic flies and wasps parasitized lepidopterous eggs con- in the Corn Belt. Reduction of over- The effect of planting date on borer hybrids lose their resistance when levels by combining grass-weed have been imported from Europe taining the larvae of a species of wintering populations might be infestations will vary depending on the corn reaches tasseling and silk- control and adult moth control. If and released in the United States to Trichogramma have been applied to important. But, research in lowa and the number of borer generations in ing. Most hybrids are susceptible cornfields are kept relatively free of control the borer. Some wasp spe- cotton by airplane for control of the Minnesota shows that borer sur- the corn production region. cies, Macrocentrus grandii and cotton bollworm, Heliothis zea, and vivorship is independent of the size Eriborus terebrans, are well estab- the tobacco budworm, H, virescens. of the previous generation. Borer a. One-generation regions. Early Table 8. Average number of larvae per plant and cumulative percentage mortality for lished and are responsible for sup- Unfortunately, there is so much varia- survivorship is quite dependent on planting of borer-resistant corn first-generation European corn borer caused by moisture stress and inundation, pressing borer populations to varying tion associated with this technique the weather conditions during adult hybrids will normally result in mini- lowa studies (W. B. Showers). extents in different locations and that the results are inconsistent. But, moth mating and egg laying and mum infestation, borer tunnels, and Moisture years. A parasitic fly, Lydella several species of Trichogramma are during borer development imrnedi- broken stalks; but presently the yield Stress Inundation potential will be lower than yield Observation thompsoni, also imported and estab- used in Europe, Central and South ately following egg hatch. days after No. larvael % larval No. lame1 % lam1 lished in the United States some America, and Asia to contrd ECB. A expected from susceptible hybrids. hatch1 plant mort./plant plant rnort.1plant years ago, disappeared in the north species, Trichogramma nubilalae, If a number of growers in a given Table 8 presents information showing 0 20.0 0 20.0 0 central region in the mid-1960s. The native to the United States bas been the effects of moisture in combina- location follow a comparable plant- 2 15.7 21.5 6.5 67.5 fly is presently reestablished in the found in Delaware. Use of tk- tion with temperature-related factors ing date, this will provide conditions 4 9.0 55.0 6.5 67.5 Middle Atlantic states and attempts species, and exotic species of (stress and-evaporation) on the sur- needed for uniform dispersal of 6 8.7 56.7 2.5 87.5 are being made to reintroduce the fly Trichogramma, for control of ECB ' vivorship of first-generation larvae on ovipositing female moths and 8 5.1 74.6 2.5 87.5 in the north central states. are under study. thereby reduce the number of egg 12 4.25 78.8 1.25 93.8 a susceptible corn hybrid. Moisture 14 3.5 82.4 1.25 93.8 stress caused relatively uniform mor- masses deposited in individual 17 2.5 87.6 1.25 93.8 A parasitic protozoan, Nosema Bacillus thuringiensis, a bacterium, tality; by the twentieth day after fields. Abundant action sites in and 20 1.8 91.1 0.8 96.0 pyrausta, weakens the borer so that produces spores and crystals toxic hatch just 1.8 borers per plant around a specific field, however, will 22 0.9 95.6 0.5 97.5 infected larvae suffer heavier winter to ECB. Commercial formulations, survived (91.1 percent mortality). In- allow larger aggregations of moths 24 0.6 97.2 0.45 97.8 kill and infected moths lay fewer both granular and liquid, are undation of the larvae, however, on and will result in larger numbers of 'All leaves of 20 corn plants examined/obse~ation. grass and dense weeds, and the Summary of One-generation Regions (table 10) Table 11. Management options, two generations. waterways and field edges are Management Tactics Establishment of ECB larvae occurs Treatment mowed, borer moths can be There are several stages during the after susceptible corn plants reach "herded" into predesignated patches corn production process where an extended leaf height of approx- Planting I st 2nd of grass [minimum size, 99 ft. (30m) growers can influence ECB popula- imately 22 inches (55 centimeters). Corn hybrid time generation generation x 494 ft. (150m)l and killed with tions through their management Infestations are indicated by larval Hybrid resistant to leaf feeding; Early as possible Scout, starting with 22 in. (56 cm) Scout, develop PPD and EIL after nonpersistent insecticides labeled decisions. Successful control of ECB feeding in the whorl and on the plant susceptible to sheath and collar extended leaf height during whorl finding first egg mass on leaf or young feeding stage; should not need to treat. larvae in leaf mils; 2 treatments may be for grasshopper control. The pre- usually can be achieved by integrat- leaves. Leaf feeding has the ap- necessary. designated patches of treated grass ing management components into pearance of "shot holes." Damage is comprehensive programs tailored to inflicted by tunneling in the leaf Hybrid susceptible Early as possible Scout, develop PPD and EIL after Scout, develop PPD and EIL after are necessary at each field where leaves show feeding and live larvae are finding first egg mass on leaf or young most grassy areas have been conditions for the particular location. midribs and in the stalk, thus reduc- present; 1 treatment should be larvae in leaf mils; 2 treatments may be mowed. These patches prevent the ing the flow of plant nutrients and sufficient. necessary. moth populations from seeking cover The design of a control program for water. Selection of resistant hybrids in untreated grass near neighboring a particular area is largely depen- and early planting dates is impor- fields and then returning to lay eggs dent on the number of generations tant. During seasons with heavy Table 12. Management options, three or four generations. in the fields with the borders and per year. This section summarizes populations, estimate the probability waterways mowed. Where corn is the typical control programs in terms of that economic injury levels (EIL) will Treatment predominate crop, this strategy is generations of corn borer per year. be exceeded. Insecticidal controls Planting I st 2nd 3rd 4th most effective on a section or more. Each narrative section below is ac- may be necessary. Hybrid time generation generation generation generation companied by a table that shows the Long-season hybrid Early as 3-generation area- Scout, develop PPD Scout, develop PPD Harvest early 3. Early Harvesting management action growers can Two-generation Regions (table 11) resistant to leaf possible scout, should not have and EIL and treat and EIL and treat if Early harvesting is a management take in successive phases of the First generation. Seasonal manage- feeding; susceptible to to treat; 4-generation if necessary; necessary; harvest sheath and collar area--no concern 2 applications, early option that will effectively reduce annual production cycle. Detailed ment practices should be the same feeding 7-10 days apart yield losses resulting from broken descriptions of these actions can be as for one-generation regions (see and lodged plants and dropped obtained by referring to the appropri- above). Long-season hybrid Early as 3-generation area- Scout, treat if Scout, treat if Harvest early susceptible to leaf possible scout and treat; necessary; necessary; harvest ears. Most corn produced in the ate sections under Components of feeding; tolerant to 4-generation area- 2 applications, early Corn Belt is subjected to infestations Management. sheath and collar no concern 7-10 days apart (I by two generations of borers. After feeding boring into the plant, the second- Long-season hybrid Early as 3-generation area- Scout, treat if Scout, treat if Harvest early generation larvae feed primarily in Table 9. Location of second-generation, fifth-instar European corn borer on susceptible to all possible scout and treat necessary; necessary; harvest the lower portion of the plant (table susceptible field corn in the Corn Belt (Iowa, W. B. Showers; Nebraska, feeding if necessary; 2 applications, early 9). It is this feeding that is responsi- J. F. Witkowski). 4-generation area- 7-10 days apart no concern ble for stalk breakage and dropped Iowa1 Nebraska2 ears. Early harvest, combined with Borers/ % of Borers/ % of Short-season hybrid Early as 3-generation area- Scout, treat if Should scout and No concern early planting, will reduce yield Plant area plant total plant total resistant to leaf possible scout, should not have necessary; treat if necessary in feeding; susceptible to to treat; Cgeneration 2 applications, 4-generation areas losses. In the southern portion of the Above the ear 0.94 29 2.0 31 sheath and collar area--no concern 7-10 days apart Corn Belt (Kansas, Kentucky, and On ear and shank 0.29 9 1.12 18 feeding Missouri), and in other southern Below the ear 2.02 62 3.21 51 Total per plant 3.25 100 6.33 100 Short-season hybrid Early as 3-generation area- Scout, treat if ~otoncernin 3- No concern regions where more than two genera- susceptible to leaf possible scout and treat necessary; generation area; scout tions occur, early harvesting of 'Iowa--Each mean composed of 360 04seGtions (10 plants x 36 replications). August, 1968. feeding; tolerant to if necessary; 2 applications, and treat if necessary 2Nebrask&Each mean composed of 80 observations (10 plants x 8 replications). August, 1978. heavily infested fields is recom- sheath and collar 4-generation are& 7-10 days apart in 4-generation area mended. If the corn can be mechan- feeding no concern L. Short-season hybrid Early as 3-generation area- Scout, treat if No concern in 3- No concern ically dried on the farm, it will Table 10. Management options, ~n~generation. probably be profitable to dry it. If no susceptible to all possible scout and treat necessary; generation area; scout on-farm drying facilities are available, Planting Treatment feeding if necessary; 2 applications, and treat if necessary Corn hybrid time 1st generation 4-generation area- 7-10 days apart in Cgeneration area it will usually be better to harvest no concern early and to sell the corn and take a Hybrid resistant to leaf feeding Plant early Scout during whorl stage; should not need to treat. 2nd crop corn-- Mid-late No concern No concern Scout, should not have Scout, treat for borer if relatively large moisture dockage. short-season hybrid season to treat for borer; will necessary; will have to Hybrid susceptible to leaf feeding Plant early Scout starting with 22 in. (56 cm) resistant to leaf have to treat for fall treat for fall armyworm extended leaf height during whorl stage; feeding armyworm develop PPD and EIL and treat if necessary; 1 treatment should be sufficient. 2nd crop corn-- Mid-late No concern No concern Scout, treat for borer Scout, treat for borer short-season hybrid season and fall armyworm at and fall armyworm at susceptible to leaf 7-10 day intervals 7-10 day intervals feeding Second generation. Oviposition by areas) and second-generation borer sweet corn and long-season vari- the ear tip, shank, and stalk that may only the tassels and record the average infestations of less than two female moths usually occurs at the populations. Long-season varieties eties usually have heavier infesta- reduce yield through the phys- number of plants that have live young larvae per infested plant. time of pollen-shed in late-planted may be severely damaged by sec- tions of larvae than do early-planted iological effect on the sweet corn larvae feeding on the tassels. It is Moderate damage is indicated by corn. Most eggs will be laid in the ond and third generations. Late- short-season varieties. The late plant. important to determine if live borers notable feeding holes and some ear zone and on the three leaves planted corn planted as a second summer populations of larvae are are present and actively feeding. Pull midrib injury on more than two-thirds above or below the ear zone. Early crop may be severely damaged generally higher in sweet corn than The damage allowed in ears of out and carefully unroll the whorl of the leaves with 10 to 50 percent of stage larvae will feed on pollen at during the whorl stage from leaf in field corn under similar conditions. sweet corn varies depending on the leaves and tassels of the first two the leaf area affected. Moderate leaf mils, in the sheath, and around feeding by the third and fourth processor or fresh market outlet. plants showing damage at each whorl injury produces many patterns the sheath collar before entering the generations of corn borer and a The major damage by borers in Some processors can tolerate up to location and note the number and of feeding holes and midrib tunnel- stalk, ear shank, and ear. Tunneling summer generation of fall armyworm, sweet corn is from direct feeding on 20 percent ears with tip damage location of live larvae found. If fall ing that are associated with average will result in broken stalks and Spodoptera frugiperda. The later the the ears. This affects acceptability of and up to 5 percent with side-kernel armyworm is present, add the infestations of two to five young dropped ears. Timing of insecticidal corn remains succulent, the greater the corn for fresh market or for damage before the quality of the number of plants infested with this larvae per infested plant. Heavy control for second generation is the potential for corn borer damage processing. Most ear damage oc- final food product is affected. Most insect to the corn borer assessment whorl injury involves extensive feed- critical, and applications must be (table 4). Most eggs are laid on the curs from larval feeding on the processors prefer little or no damage because a management decision is ing on all leaves with greater than 50 made soon after hatch and before ear, on the ear leaf, and on the three kernels along the side of the ear and in some cases provide a bonus based on the combined infestation percent of the leaf area affected. the larvae migrate to the ear tip, or leaves above and the three leaves (figure 15). Many processors feel the for insect-free corn. Fresh market of both insects. deep into the leaf mils, the sheath, below the ear zone. Larval feeding in European corn borer is a more outlets generally tolerate less ear The timing for spraying silking sweet and collar, and before they enter the the ear shank and ear of early- serious problem than the corn ear- damage than processors. Light whorl feeding is defined as corn is best determined by the stalk or ear shank. A second ap- planted corn is greater in the third- worm because of the difficulty in superficial "window pane" damage number of moths captured in black- plication may be needed in 7 to 10 and fourth-generation regions. Insec- detecting the infested kernels on the Detection and Assessment with a few scattered shot holes on light traps and by the extent of egg days. Determine treatment window ticidal control for European corn side of the ear and consequently the The presence of egg masses on the less than half of the leaves. Injury of laying and larval feeding during the and develop potential population borer on second crop corn should increased likelihood of insect con- underside of leaves (figure 4) and this type is generally associated with presilking stages of later plantings densities (PPD) and economic injury be timed the same as for first tamination of the food product. young larvae feeding on the whorl levels (EIL) after the first egg mass generation in the two-generation Additional damage occurs from leaves, tassels, and silks are the or early stage larvae in the leaf mils areas. Insecticidal control for corn feeding on the leaves and boring in best indications of infestation. A Figure 16. Blacklight trap equipped with 15-watt bulb, photocell, and 12-volt battery. have been found on plants in pre- to borer on the first crop corn should blacklight trap (figure 16) is a useful post-tasseling stage of development. be timed the same as for the first tool for determining the presence of Extremely late-planted corn will be and second generations in the two- Figure 15. European corn borer larvae feeding potential egg-laying females in the attacked during the whorl stage by generation regions. A second ap- on ear kernels. vicinity of sweet corn. Pheromone second-generation borers. Also, plication usually will be necessary 7 traps also may be considered, al- there is a correlation between large to 10 days after the first application. though they generally have not been numbers of European corn borer, Early harvest is important. High corn as reliable as light traps or direct stalk rot, and aflatoxins. borer populations may increase inci- sampling. Sampling in grasses along dence of stalk rot and aflatoxins. field edges and waterways for adults Three- or More-generation (figure 11) may prove beneficial in Regions (table 12) European Corn Borer on assessing populations. First generation. Normally in four- Commodities Other than generation areas, the first generation Field Corn The time to sample for borer feeding will develop on early hosts, both activity in early plantings of sweet economic and noneconomic, before Sweet Corn corn can be determined by the corn is available. In three-generation Life History and Damage capture of moths in blacklight traps. areas, management practices should The life cycle of the European corn Sampling usually begins when the be similar to two-generation regions borer on sweet corn is very.s'i%Har to earliest fields reach the early whorl (table 11). that on field corn. Large populations stage of plant development. During of larvae on plants usually result the whorl stages, inspect the whorl Second and third (or subsequent) when oviposition has taken place leaves of 20 plants in each of five generations. During the whorl stage between early whorl and fresh silk locations and record the number of of corn development, early-planted stages of sweet corn development. egg masses and plants showing short- or medium-season varieties The most vulnerable time for ear light, moderate, and heavy feeding. will normally receive infestations from infestations is when oviposition oc- During the period when the tassels the first (only in three-generation curs during silking. Late-planted are emerging from the whorl, inspect on the same farm. Direct sampling considerations for other pest insects; ment practices is suggested if 50 PC = Proportion of the European In this example, the benefit exceeds 2. There is one or more eggs of an for the corn borer and other ear- i.e., corn earworm, armyworms, and percent or more of the plants show corn borers controlled (expected to the cost of control by $3 per acre. ear-damaging insect in the silk of the damaging insects during the silking sap beetles. When selecting the fresh whorl injury and have live be killed by the insecticide) This indicates the need for control. primary ear; or period of fresh market sweet corn is insecticides, consideration also borers in the whorl. For more precise MV = Sweet corn market value in There may not be a sufficient benefit marginally effective because of the should be given to beneficial insects decisions, the following equation can dollars per ton margin, however, to justify control, 3. A young larva of the borer (or any low economic injury levels. However, such as bees and natural enemies. be used to calculate the anticipated EY = Expected yield in tons per especially when considering other other ear-damaging insect) is feed- assessments of egg and larval The decision process is further com- benefit to be gained by a whorl acre factors. These factors include the ing in the silk. stages during silking of sweet corn plicated by the fact that low levels of application of insecticide based on time involved in lining up the ap- that will be processed can be made damage are allowed for the ears, economic factors and the extent of In the example that follows, assume plicator, impact on other farm If less than 100 percent of the sweet by inspecting 20 plants while the and insecticide treatment is the only whorl feeding. The benefit should be that PLD = 15 percent, PMD = 30 operations, environmental concerns, corn plants are silking, the number primary ear is in silk. Samples reliable means of keeping injury compared with the control cost to percent, and PHD = 10 percent. and the amount of risk the grower is of ears vulnerable for damage on should be taken at each of five levels low. Therefore the present arrive at a management decision. If Also, the proportion of borers ex- willing to take. plants in criteria two and three must locations throughout a field. Records decision-making procedures devel- the benefit exceeds the cost of pected to be controlled (PC) by be adjusted to the percentage of are taken on the percentage of oped for seed and field corn do not control, then the cost of treatment is insecticide application is 0.67, the Decisions to treat processing sweet plants with silking ears. During fresh plants carrying egg masses and the fit the circumstances for sweet corn. economically feasible. market value (MV) is $60 per ton, corn during silking are based on the silk (18 to 20 days before harvest), percentage of primary ears infested and the expected yield (EY) is 3.5 percentage of ears that are poten- treat if 5 percent or more of the with eggs or young larvae of an ear- The criteria for treating processing Benefit = ((0.0008 x PLD) + tons per acre. The total cost of tially damaged by the presence of plants in silk meet one or more of damaging insect. sweet corn for borer control (figure (0.0024 x PMD) + (0.0044 x control for one application is $15 per eggs andlor young larvae of ear- the above criteria. During wilted silk 17) are different than for fresh market PHD)) x PC x MV x EY acre. The economic benefit would damaging insects (figure 17). A pri- (about 16 to 18 days before harvest), Management Decisions because economic injury levels are be: mary ear is potentially damaged if it treat if 10 percent of the plants fall Management of European corn borer much higher and the raw product is where: meets one of the following criteria: into one or more of the above and other sweet corn insects con- marketed on a weight basis rather PLD, PMD, and PHD = Percentage Benefit = ((0.008 x 15) + (0.0024 criteria. At the onset of 100 percent sists of careful assessment of than by the dozen. As a general of plants infested with live larvae and x 30) + (0.0044 x 10)) x 0.67 x 1. The plant carries one or more brown silk on primary ears (10 to 12 population levels and timely applica- guideline before silking, whorl treat- showing light, moderate, or heavy 60 x 3.5 unhatched egg masses of the borer days before harvest), treat if 20 tion of insecticides. Decisions for ment of sweet corn grown for whorl feeding, respectively Benefit = $18 per acre (or any other ear-damaging insect); percent of the ears have larvae treatment of sweet corn must include processing under average manage-

Figure 18. Management decisions for European corn borer on fresh market sweet corn.

Figure 17. Management decisions for European corn borer on processing sweet corn. Examine field for plant development stage and sample for pest insects

Examine field for plant development stage and sample for pest insects Whorl Emerging tassel Silk Silk Whorl Fresh silk Wilted silk Brown silk (when corn earworrn (when corn earworm I I is absent) is present) I I I I

masses or with eggs masses or with eggs larvae on earwonn activity on silk or with young on silk or with young tassels larvae on silks larvae on silks with live in adjacent live larvae larvae No Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes

I I I Depending on pest population, treat every 2-6 days after initial silk I Monitor blacklight and adjacent plantings emerging tassel I I I Monitor field at next appropriate stage of growth I feeding on the silks and the larvae upon the overall activity of both age are particularly large when EIL similar to those calculated for borers counted daily. Thresholds for Snap Beans are exposed enough to be killed by insects. popcorn is infested during pollen field corn at pollen shedding. Pop- treatment consist of four or more Life History insecticides. shed or postpollen shed and can corn value is approximately $0.10 female moths per blacklight trap per Snap beans are incidental hosts of Maximum control during silking is average as much as 25 percent of per pound and yield is usually night for three consecutive nights. the European corn borer. Economic The criteria for treating fresh market achieved with high volume sprays of the total yield. The borer causes very expressed as pounds per acre. Local phenology models for the problems can occur before preferred sweet corn for European corn borer insecticides using a high clearance little direct damage to popcorn ker- European corn borer are useful in hosts are available, after preferred or fall armyworm control (figure 18) boom applicator with solid cone nels, probably because of the hard, Peppers predicting the second generation. It hosts dry up and become unattrac- before tasseling are for 30 percent or nozzles dropped between rows and starchy nature of the kernels. Life History and Damage is useful also to inspect nearby corn tive, or when corn borer populations more of the plants to show leaf directed at the ear zone. Aerial The life history of the European corn for egg masses or whorl feeding. are extremely high. Corn borer in- feeding in the whorl and have live application and air-blast sprayers Table 13 shows yields of IOPOP 12 borer on peppers usually involves The results of recent research in festation of snap beans occurs larvae or when 20 or more un- also provide adequate coverage if popcorn hybrid (the most widely the midsummer and late genera- lowa suggest that nearby late- primarily in late spring (before corn hatched egg masses are found per used at maximum spray volume. The grown popcorn hybrid in the Mid- tions. Occasionally, early summer planted sweet corn can serve as a is available) or in midsummer. Egg 100 plants. Usually one whorl ap- number of rows to be sprayed by air- west) in pounds per acre when larvae are found on transplants that trap crop with fewer egg masses masses are deposited on leaves plication of insecticide is sufficient to blast application should be adjusted infested by 0, 0.5, 1.O, 2.0, and 4.0 were infested in the seed beds. Egg being deposited on peppers. Be- about the time of blooming. The prevent economic loss in the number to the canopy structure of the variety. European corn borer egg masses masses are usually deposited on cause of the low threshold of infesta- larvae hatch in about 4 days and of marketable ears. Foliar treatments Extensions also can be added to per plant. Yield losses were large leaves. The eggs hatch in 3 to 7 tion tolerated for peppers for pro- disperse over the plant. First- and of granules or high volume sprays certain applicators to direct the air with just 0.5 egg masses per plant. days and the larvae disperse over cessing, it is impractical to sample second-stage larvae usually feed on directed in the whorl by ground blast down through the canopy, thus Table 13 shows that losses in excess the plant. First-stage larvae enter the for egg masses or larval stages. leaf tissue, particularly new tissue. applicators are the most effective. improving the spray distribution of 1,000 pounds per acre can occur. upper part of the fruit by crawling Second- and third-stage larvae will For early tassel infestations, treat if across the rows. For ground applica- under the calyx and boring into it or Management Decisions feed on leaf petioles and in axils. 15 percent or more of the plants tion, high volume sprays of 50 to 75 Detection into the fruit wall. First- and second- When pepper fruits are forming on Larvae may bore in stems and have live borers or fall armyworms gallons per acre should be used Scout for damage and live larvae on instar larvae feed on the calyx, flesh plants, insecticide treatment should petioles before pods are present and feeding in the emerging tassels. As whenever possible. whorl stage popcorn. During pollen around the calyx, or in the placenta. begin when an average of four or then enter pods after they form. the tassels emerge, larvae disperse shed and postpollen shed, scout for Third-stage larvae may continue more female moths per light trap are to other plant parts and thus are When treating with insecticides, be egg masses on leaves or young feeding on the pepper fruit, or may collected per night for three con- The impact of infestation on growth more exposed to insecticide at this sure to observe the label restrictions larvae in leaf axils of popcorn. leave the fruit. Those leaving the fruit secutive nights. Once insecticide and development of the plant is time. Larvae present during tasseling for the minimum number of days commonly bore into uninfested fruit applications have begun, they mimmal. The major problem is borer also have a greater chance to invade before harvest. Note: application of Management Decisions or into stems. Larvae continue to should continue on a 7-day sched- contamination of pods in snap the developing ear, causing a quality insecticide during pollen shedding Develop PPD and EIL similar to develop and may pupate in fruit or ule until harvest. It is important to beans used for processing. Toler- problem. can seriously reduce bee popula- those calculated for whorl stage field stems. Or, if late enough in the maintain this schedule because of ance of infested pods is quite low. It tions. If an insecticide must be corn. One treatment should be suffi- season, larvae may go into diapause the low infestation level for rejection varies among processors, ranging The criteria for treating (figure 18) applied, select a material with low cient. During pollen shed and and overwinter in stems and fruit of the crop. When 10 percent or from 0.2 to 1 infested pod per 1,000 fresh market sweet corn during silk- toxicity to bees. Apply it during late postpollen shed, develop PPD and peduncles. more of the peppers are infested pods. A single sample with an ing are generally based on the evening since bees usually forage with corn borer at delivery for pro- infestation at or above the tolerance extent of corn earworm (one moth corn for pollen only in the morning Early-infested fruit usually rot and cessing, the entire crop is rejected. level usually results in the harvest of per night) activity in blacklight traps. and not in the afternoon. Table 13. Pounds per acre of IOPOP 12 drop off the plant. Fruit infested late For peppers to be processed whole, an entire field or farm being rejected However, for plantings that are silking popcorn after infestation with several in development may appear healthy, such as for pickling, the threshold for for processing. when the earworm is absent, begin Popcorn levels of European corn borer (Polk but are rejected upon marketing or rejection may be as low as 1 to 5 b County, lowa, J. L. Jawis).' treatments at the first sign of silking Life History and Damage processing because of contamina- percent. Detection if corn borer catches in blacklight The life cycle of the Europehn corn Mean number of egg tion. Damage due to feeding around Moth catch in blacklight traps traps exceed five moths per night, or borer on popcorn is very similar to masses/plant Yields, Ib./A the calyx may also reduce the Insecticides can be applied with placed near the bean field is the if egg laying and leaf feeding are field or sweet corn. Popcoq !5 lnfestation during whorl stage quality of fruit that escape internal either conventional ground or aerial best indicator of potential corn borer evident on the presilk stages of susceptible to ECB damage and will 0 41 60 infestation. spray equipment. If adequate control infestations. The presence of egg 0.5 3575 younger plantings on the same farm. have considerable yield losses when 1 .O 3510 is to be obtained, generally the masses on nearby corn, if available, Levels of 10 or more egg masses per infested during plant growth stages, 2.0 2990 Detection insecticide used must have residual is also a good indicator. Since there 100 plants or more than 15 percent mid-whorl to 4 weeks postpollen 4.0 2730 A blacklight trap to detect adult activity for about 7 to 10 days. is such a low tolerance level of corn of the plants showing fresh feeding shed. Infestation during pollen shedding stage females in or near the pepper field Consult your Cooperative Extension borer on snap beans, it is imprac- indicate that corn borer and/or fall 0 4290 should be operating before the sec- Service for recommendations on in- tical to survey for egg masses or armyworm moths are laying eggs in The major damage to popcorn by 0.5 3445 ond generation of corn borer is secticides and rates of application. larvae on the beans. nearby plantings-in-silk. Repeat ECB is similar to damage in field 1.O 3250 anticipated. Insects collected in the Also, note preharvest time and re- sprays every 4 to 6 days depending corn. Yield losses from stalk break- 2.0 3120 trap should be removed and female strictions stated for treatment. 4.0 2730 North Central Regional Extension Michigan Wisconsin Management Decisions material, or frass, at these axils is a Other Crops Publications are subject to peer Bulletin Office Agricultural Bulletin, Room 245 Insecticide treatment should begin at good indicator of the presence of Since the European corn borer is a review and prepared as a part of the P.O. Box 6640 30 N. Murray St. 8 to 10 days before bloom when an ECB larvae. A later generation of polyphagous insect, it has been Cooperative Extension activities of Michigan State University University of Wisconsin average of five or more moths per moths may lay eggs before harvest. reported on a number of other crops. the thirteen land-grant universities of East Lansing, Michigan 48826-6640 Madison, Wisconsin 53715 night are captured in local light traps Some of these include apple, cotton, the 12 North Central States, in (515) 355-0240 (608) 262-3346 or when egg masses found on The economic impact of corn borer lima bean, soybean, small grains, cooperation with the Extension nearby corn exceed 10 per 100 on potato has not been determined. sorghum, tomato, and onion. When Service-U.S. Department of Agri- Minnesota For copies of this and other North plants. Repeat treatments at 7-day Studies on the direct effect of corn ECB is found on these crops, it is culture, Washington, D.C. The Distribution Center Central Regional Extension publica- intervals if moth captures in light borer on yield reduction have not generally from incidental infestations following states cooperated in mak- 3 Coffey Hall tions, write to: Publications Office, traps average 5 to 10. Treat at 5-day shown losses to the extent that resulting from high populations in ing this publication available. University of Minnesota Cooperative Extension Service, in intervals if moth captures average 10 warrant treatment. There has been corn. Occasionally, isolated cases St. Paul, Minnesota 55108 care of the University listed above for to 20, treat every 4 days if captures some concern about corn borer can be found where rather heavy Illinois (612) 625-8173 your state. If they do not have copies average 20 to 50, and treat every 3 damage predisposing the potato infestations occur. These may result Ag Publication Office or your state is not listed above, days if captures exceed 50 moths plant to the bacterial soft rot orga- in economic losses depending on 54 Mumford Hall Missouri contact the publishing state as per night. nism Erwinia carotovora. Indoor stud- the value of the crop. Crops with a University of Illinois Extension Publications specified. ies show that plants can be infected high value and low consumer toler- Urbana, Illinois 61801 115 S. Fifth St. by artificially inoculating the bac- ance for damage, such as apples, Potato (217) 333-2007 University of Missouri *Publishing state European corn borer is known to terium at borer entrance holes. can have a significant economic loss Columbia, Missouri 65211 infest potatoes in several areas of the However, natural inoculation in the due to borer feeding. lndiana (314) 882-2792 In cooperation with NCR Educational United States. Eggs are deposited field is probably minimal because Publication Mailing Room Materials Project. by early season adults on the under- the bacteria are generally found on 301 S. Second Street Nebraska Issued in furtherance of Cooperative side of leaves of young plants. the plant near the soil and the larvae Purdue University Department of Ag Communications Extension work. Acts of Congress of Larvae enter potato vines by tunnel- usually enter the stem fairly high up Lafayette, lndiana 47905-1092 University of Nebraska May 8 and June 30, 1914, in ing through the stems, usually in the on the plant. (317) 494-6795 Lincoln, Nebraska 68583-0918 cooperation with the U.S. leaf axil at the node. The fecal (402) 472-3023 Department of Agriculture and 'Iowa Capperative Extension Services of Publications Distribution North Dakota Illinois, Indiana, Kansas, Michigan, Printing and Publications Bldg. Ag Communications Minnesota, Missouri, Nebraska, lowa State University Box 5655, Morrill Hall North Dakota, Ohio, South Dakota, Ames, lowa 50011 North Dakota State University and Wisconsin. Elizabeth A. Elliott, (515) 294-5247 Fargo, North Dakota 58105 interim director, Cooperative (701) 237-7881 Extension Service, lowa State Kansas University, Ames, lowa 50011. Distribution Center Ohio Umberger Hall Rm. 14 Publications Office and justice for all Kansas State University Ohio State University Cooperative Extension Service pro- Manhattan, Kansas 66506 2120 Fyffe Road grams and policies are consistent (913) 532-5830 Columbus, Ohio 43210 with pertinent federal and state laws (614) 292-1607 and regulations on non-discrimina- tion regarding race, color, national South Dakota origin, religion, sex, age, and Q.. -. Ag. Comm. Center handicap. Box 2231 South Dakota State University Brookings, South Dakota 57007 (605) 688-5628