160 Journal of Nematology, Volume 10, No. 2, April 1978

, Ditylenchus destructor. Ann. Appl. abilit~it und Mutationen bei Nematoden. Zesz. Biol. 39:468-474. Prob. Post. Nauk Roln. 92 (Proc. 1X Int. 6. LOOF, P. A. A. 1960. Taxonomic studies on the Nem. Symp. (Warsaw, 1967)):209-220. genus Pratylenchus (Nematoda). Tijdschr. 12. TARJAN, A. C. 1967. Variability of diagnostic Plantenziekten. 66:29-90. characters among some plant and soil nema- 7. O'BANNON, J. H., A. C. TARJAN, attd F. W. todes. [Polish text]. Prace Nauk. Inst. Ochrony B1STLINE. 1974. Control of Pratylenchus Roslin 9(1):105-116. brachyurus on citrus and tree response to 13. TARJAN, A. C., and J. H. O'BANNON. chemical treatment. Proe. Soil Crop Sci. Fla. 1969. Observations on meadow 33:65-67. (Pratylenchus spp.) and their relation to 8. O'BANNON, J. H., and A. T. TOMERLIN. declines of citrus in Florida. Plant Dis. Rep. 1973. Citrus tree decline caused by 53(9) :683-686. Pratylenchus coffeae. J, Nematol. 5:311-316. 14. TARTt~, R., and W. F. MAI. 1976. Morpho- 9. ROMAN, J., and H, HIRSCHMANN. 1969. logical variation in Pratylenchus penetrans. Morphology and morphometrics of six spe- J. Nematol. 8:185-195. cies of Pratylenchus. J. Nematol. 1:363-386. 15. THORNE, G., and M. W. ALLEN. 1959. Varia- 10. SHER, S, A., and M. W. ALLEN. 1953. Revision tion in nematodes, pgs. 412-418. In Holton, of the genus Pratylenchus (Nematoda: C. S. ed., problems and Tylenchidae). Univ. Calif. Publ. Zool. 57: 441- progress. 1908-1958. Univ. Wisconsin Press, 470. 588 pp. 11. STURHAN, D. 1970. Intraspezifische Vari-

Corn Yield Increases Relative to Nonfumigant Chemical Control of Nematodes 1 DON C. NORTON", JON TOLLEFSON 3, PAUL HINZ 4, and STEPHEN H. THOMAS 2 Abstract: Corn yields were measured after application of nematicides in 16 experiments, mostly in medium-to-heavily textured soil, at 12 locations in Iowa during 1973-1976. The average maximum yield increase in plots treated with nematicides was 21% over yields in untreated plots. Yields were correlated negatively with nematode numbers or nematode biomass in nearly all comparisons. Correlations of nematode numbers in the soil with yield averaged --0.56 for Helicotylenchus pseudorobustus, --0.45 for , --0.51 for Pratylenchus spp., and --0.64 for americanum. Correlation coefficients for numbers of nematodes in the and yield averaged --0.63 for Pratylenchus spp. and --0.56 H. galeatus. Correlation co- efficients for yield and total number of nematodes averaged --0.65 in roots and --0.55 in soils. Negative correlations also were greater for comparisons of yield with total parasitic-nematode biomass than with numbers of individual nematodes of a species or total numbers of parasitic nematodes. Key Words: Helicotylenehus pseudorobustus, Hoplolaimus galeatus, Pratylenchus hexincisus, Xiphinema americanum, rootworms.

Nematodes have been associated with production over wide areas of the upper corn, Zea mays L., from the upper mid- Midwest, where medium-to-heavily textured western United States (4, 8, 14, 18). soils predominate, [lave not been evaluated Nematicides have reduced the density of fully. Smolik (16) found a negative correla- nematode populations around corn and tion of yield with parasitic nematodes at have been associated with increased yields harvest in South Dakota. Hoplolaimus (7, 10). The effects of nematodes on corn galeatus (Cobb) Thorne and Pratylenchus hexincisus Taylor 8c Jenkins were impli- Received for publication 14 March 1977. cated in corn yield losses in sandy soils in 1Journal Paper No. J-8770 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011. Iowa (13). Rootworms, wireworms, ear- Projects 1991 and 2119. This study was supported, in part, worms, or stalk rot were not present or by Grant No. R-802547 of the Environmental Protection Agency. Acknowledgment is made to John Owens for use were not affected by the treatments in these o~ his plots in 1974. tests. This research was done to determine =,3,*Departments of Botany and Plant Pathology, Entomol- ogy, and Statistics. Iowa State University, Ames. the role of nematodes as a factor in in- Nematodes on Corn: Norton et al. 161 creased corn yields in plots treated with extraction, the roots were dried at 90 C for nematicides in medium-to-heavily textured 48 h. soils. Correlations: Correlations were tested between corn yields and numbers of soil nematodes/100 cm a, total nematode bio- MATERIALS AND METHODS mass in soil, total numbers of nematodes in General procedures: The results re- roots, and total nematode biomass in roots. ported are from 16 experiments at 12 The higher of the two nematode counts was locations during 1973-1976. The experi- used for calculating correlation coefficients ments were in all sections of iowa except (r). the southwestern part. Two experiments Prominence vahte: Used to ascertain were in soil containing more than 90% relative quantitative values among nema- sand, but all others were in loam, silt loam, todes was the prominence value, PV = or clay loam soils. Five locations were density ~/frequency (2). Values were calcu- suspected of having a nematode problem. lated from mean numbers of nematodes in The other 11 test sites were not pre- untreated plots in tile mid-to-late-summer viously assayed. Granular nematicides samplings. applied were aldicarb, carbofuran, 0[5- Biomass: More juveniles than adult chloro-l-(1-methyl)-I H-l,2,4-triazol-3-yl]O,O- nematodes were present in mid-to-late sum- diethyl phosphorothioate (CGA-12223), met in iowa. To estimate biomass, 25-30 ethoprop, fensulfothion, phenamiphos, and nematodes of each species were picked at terbufos. Nematicides were applied in a random from midseason samples and meas- 17.8-cm band unless specified otherwise. ured, and the biomass was calculated by the Granules were applied with tractor- formula of Andrassy (1). The biomass for mounted applicators or calibrated gear- individual nematode species used in this driven, hand-operated applicators and study was: Helicotylenchus pseudorobustus incorporated into the top 5 cm of soil. Row (Steiner) Golden, 0.183 t~g; Hoplolaimus widths were 71-76 cm. Most plots were four galeatus, 0.792/~g; Pratylenchus spp., mostly rows wide and 9.1 m long. The two outer P. hexincisus, 0.072 t~g; Paratylenchus rows were sampled within the row for projectus Jenkins, 0.032 t~g; Longidorus nematodes, and the center 7.6 m of the breviannulalus Norton and Hoffmann, inner rows was harvested by hand for 4.657 ug; Quinisulcius acutus (Allen) yield. A composite of ten 2-cm core Siddiqui, 0.154 t'g; Trichodorus sp., 0.659 samples/15.2 m of row was sampled from ~g; Tylenchorhynchus nudus Allen, 0.125 each treatment about mid-June, mid-to-late #g; and Xiphinema americanum Cobb, July, and late August to early September. 0.995 #g. A pretreatment sample was collected from Rootworms: In an attempt to iden- the untreated plots, but because of small tify the degree of rootworm [Diabrotica nematode numbers, the data are not in- longicornis (Say), 1). virgifera LeConte, and cluded. Each treatment was replicated 4 to 1). undecimpunctata Barber] control by 7 times. All tests were of a randomized tile chemicals, 10 of the 16 experiments block design. The nmnber of treatments were evaluated for rootworm damage. The per experiment ranged from 4 to 10, in- amount of damage was classified by a cluding an untreated control. Cultivars l-to-6 visual rating, from little to a/most- varied with experiment. complete root damage. Evaluations were Tile soil in each sample was mixed made on five plants from each treatment thoroughly in the laboratory by rolling, and plot in mid-to-late July, when maximum 100 cm a was processed by the centrifugal- feeding has occurred. flotation method (9) within 2 days of sampling. Fibrous roots collected from the RESULTS soil samples were processed for endopara- Prominence values for the parasitic sites by thin-layer water extraction for 7 nematodes/100 cm a soil in all replications days, with a change of water after the third of the untreated plots for all tests were: day, in 1973-1974, and by a shaker metlmd H. pseudorobustus, 698; H. galeatus, 342; (3) for 4 days in 1975-1976. After nematode Pratylenchus spp., 318; X. arnericanurn, 162 Journal of Nematology, Volume 10, No. 2, April 1978 104; T. nudus, 33; L. breviannulatus, 0.2; duction in the Midwest. Measures of the P. projectus, 0.1; Q. acutus, 0.1; and Tri- degree of nematode were corre- chodorus sp., 0.1. Prominence values/gin lated negatively with corn yields for 58 of dry root were: Pratylenchus spp., 3,960; and 60 such comparisons made with individual H. galeatus, 833. species. Correlation of nematode numbers The average percentage yield increase in the soil with yield averaged --0.56 for in chemically treated plots compared with Helicotylenchus pseudorobustus, --0.45 no treatment ranged from 2 to 20% (Table for Hoplolaimus galeatus, -0.51 for 1). In comparison with controls, the maxi- Pratylenchus spp., and -0.64 for Xiphinema mum yield increases in the 16 experiments americanum. Correlation coefficients for averaged 21%, with the greatest increase numbers of nematodes in the roots and in any experiment being 72%, for carbo- yield averaged -0.63 for Pratylenchus spp. furan at 1.12 kg/ha. In general, however, and --0.56 for H. galeatus. Numbers of carbofuran generally resulted in greater Pratylenchus spp. and H. galeatus com- yield increase at 2.24 kg/ha than at the bined were more closely correlated with lower rates. yield than were numbers of either con- The nematicides were selective in re- sidered singly in 71% of the instances ducing nematode numbers (Table 2). For where these measures were compared. example, CGA-12223 performed well Numbers of H. pseudorobustus, H. galeatus, against H. galeatus in the roots but did Pratylenchus spp., and X. americanum in poorly against X. americanum in the soil. the soil were less closely correlated with Carbofuran generally performed best yield than were all nematodes combined in against X. americanum. 46, 60, 50, and 30% of such comparisons, The yield increases obtained with respectively. nematicides (Table 1) and reductions in Nematode biomass of individual species nematode number after nematicide appli- was more closely related to yield than cation (Table 2) give supportive evidence nematode numbers in 61% of the com- that nematodes may be limiting corn pro- parisons. Total nematode biomass was more

TABLE 1. Average yields and average percentage yield increases in corn plots treated with granular nematieides in Iowa (1973-1976).

Average percentage ~ncrease compared Averageyield in with untreated treated plots Nematicide Kg(a.i.)/ha n ~ plotsb (kg/ha)

Terbufos 1.12 4 20 6,528 Aldicarb 3.36 2 17 10,668 Ethoprop 2.24 7 17 7,163 CGA-12223c 1.68 1 17 5,207 Aldicarb 2.24 2 15 6,706 Fensulfothion 2.24 6 15 6,833 Carbofuran 2.24 16 15 7,722 CGA-12223 3.36 7 14 8,967 CGA-12223 2.24-2.80 8 13 8,027 Ethoprop 1.12 7 12 6,833 Ethoprop 3.36 1 11 4,217 Phenamiphos 4.48 1 10 4,090 CGA-12223 4.20-4.48 3 9 7,163 Carbofuran 0.84-1.12 13 8 7,163 Carbofuran 4.48 2 6 7,976 Carbofuran (furrow) 2.24 3 4 9,525 Carbofuran 3.36 2 3 5,766 CGA-12223 1.12-1.40 6 2 5,588

"Number of tests in which the chemical was used at specified rate. bBased on combined yields in all tests. cO [5-chloro-l-(1-methylethyl)-I H-l,2,4-triazol-3-yl] O,O-diethyl phosphorothioate. Nematodes on Corn: Norton et al. 163

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,~ ~ ~ ~ ~ ~ ~OOOOO az ~:-= ~ ~ ~. 164 Journal o[ Nematology, Volume 10, No. 2, April 1978 closely related to yield of corn than was DISCUSSION biomass of individual species in 66% of the instances where this comparison was Negative correlations of nematodes with made. As an example, in a test at Ames in yield are not proof that nematodes are the 1974 the correlation coefficients between cause of yield reduction. But they support yield and nematodes in tile roots were re- the hypothesis that nematodes cause signif- spectively r = -0.78, -0.86, and -0.96 for icant damage to corn. Other factors must be Pratylenchus spp., H. galeatus, and both considered in judging the importance of in- nematodes combined. dividual species. For example, even though Quantitative measures of nematode significant negative correlation coefficients presence and yield o[ corn tended to be were obtained with H. pseudorobustus and most closely related at the high end of the corn yield, and Taylor (17) found that this scale measuring nematode presence. At the nematode disrupts cortical cells, there is high end of the scale the nematodes would other evidence that this species (12) and be more apt to be a principal factor limit- H. dihystera (15) are only moderately or ing growth. slightly pathogenic to corn. Little is known Rootworms: The mean rootworm dam- about the effects of X. americanum on corn. age rating was 3.2, with a range of 0 to 5.9 In contrast, Pratylenchus spp. are well- in treated plots in the 10 tests. Although known pathogens to many crops, including any interaction between rootworm damage annuals, and evidence is accumulating that and nematodes is riot clear, the correlation different species are detrimental to corn of rootworm damage rating and maximum (5, 10). Since some of the highest yields nematode biomass in the roots was --0.741 were from plots treated with aldicarb, (P -- 0.05). The two highest rootworm which is ineffective against rootworms but damage ratings were 5.9 and 4.2, respec- highly effective against nematodes, it is tively in the untreated plots at Newell and probable that nematode control accounts Independence. Those plots had nematode for much of the yield increases obtained biomass readings in the root of 21 and 14 when this chemical was used. t~g/gm dry root in 1973 and 1974, respec- The greatest yield increases (over un- tively. treated controls) in the 16 experiments

TABLE 3. Maximum correlation coefficient (r) values in second or third samplings of nematode num- bers or biomass wi.th corn yield in Iowa (1973-1976).

Soil Roots Total soil Total nematode Total root Total nematode Location Year nematodes biomass nematodes biomass

Fort Madison 1973 --0.23 --0.26 --0.32 --0.34 Vincennes 1973 --0.58 --0.70 *" --0.81" --0.68 Ames 1974 --0.88**" --0.92** --0.86** --0.97** Chariton 1974 --0.45 --0.38 -- -- Fort Madison 1974 --0.70* --0.78** --0.50 --0.52 Garnavillo 1974 --0.32 --0.48 --0.61 --0.68 Gilbert 1974 --0.28 --0.65 --0.73 --0.85* Independence 1974 --0.62 --0.42 --0.70 + 0.17 Manley 1974 --0.50 --0.55 -- -- Newell 1974 --0.40 --0.46 -- -- Chariton 1975 --0.95"* --0.95"* -- -- Melvin 1975 --0.25 --0.10 -- -- Sanborn 1975 --0.33 --0.54 -- -- Story City 1975 --0.82 --0.71 -- -- Melvin 1976 --0.70" --0.73" -- -- Story City 1976 --0.74* --0.13" -- --

aAsterisks (*, **) respecti.vely indicate significance at P ~ 0.05 and 0.01. Nematodes on Corn: Norton et al. 165 LITERATURE CITED 12.5~ aotdicIrb 3.38 kg. 1. ANDRASSY, 1. 1956. The determination of 12.~ volume and weight of nematodes. Acta Zool. (Hungarian Acad. Sci. 2(1-3):1-15. in B. M. CGA-12223-- 3.36 kg. Zuckerman, W. F. Mai, and R. A. Rohde 11.9 (eds). English translation of selected~ East CGA-12223--2.24 kg. European papers in hematology. Univ. Mass. 1967. 11.7 r • -0.823 ° 2. BEALS, E. 1960. Forest bi,rd communities in .o the Apostle Islands of Wisconsin. Wilson Bull. 72:156-181. '~ 11,4 3. BIRD, G. W. 1971. Influence of incubation carbofur#n- 2.24 kg.~ solution on the rate of recovery of Pratylen-

11,2 - .;~'~.~-4 d,,, chus brachyurus from cotton roots. J. kg.kg. \ Nematol. 3:378-385. • ~ ne°ntreated 4. CASTANER, D. 1963. Nematode populations in corn plots receiving different soil amend- ments. Proc. Iowa Acad. Sci. 70:107-113. v10.7 5. EGUNJOBI, O. A. 1974. Nematodes and growth in Nigeria. I. Population dynamics of Pratylenchus brachyurus in and about the 10.4 roots of maize and its effect on maize produc- tion at Ibadan. Nematologica 20:181-186. 6. FELDMESSER, J. (Chairman). 1971. Estimated 10.~ I I I I I I crop losses from plant-parasitic nematodes I00 200 300 400 000 600 in the United States. Soc. Nematol. Spec. Pratylonchus spp./g, dry root Publ. 1. 7 p. FIG. 1. Number of Pratylenehus spp. and yield 7. FERRIS, J. M. 1967. Factors influencing the population fluctuation of Pratylenchns pene- of corn after treatment with nematicides. Melvin, trans ill soils of high organic content. I. Iowa (1975). Effect of soil fumigants and different crop averaged 21%. Because few fields were plants. J. Econ. Entomol. 60:1708-1714. selected for high nematode populations, 8. GRIFFIN, G. D. 1964. Association of nematodes there was a certain amount of randomness with corn in Wisconsin. Plant Dis. Rep. 48: 458-459. built into site selection. If even 50% of the 9. JENKINS, W. R. 1964. A rapid centrifugal- yield increases were due to nematode con- flotation technique for separating nematodes trol, the loss for Iowa would exceed the from soil. Plant Dis. Rep. 48:692. average estimate of loss due to nematodes 10. JOHNSON, A. W., and R. B. CHALFANT. for all corn acreage in the United States 1973. Influence of organic pesticides on nematode and corn earworm damage and on during 1967-68 (6). yield of sweet corn. J. Nematol. 5:177-180. The trends of larger negative r-values I 1. MARGALEF, R. 1968, Perspectives in ecological with increased nematodes probably have theory. Univ. Chicago Press. Chicago. 111 p. biological meaning because the presence of 12. NORTON, D. C. 1977. Helicotylenchus pseudo- more nematodes, and therefore a greater robustus as a pathogen on corn, and its densities on corn and . Iowa State J. biomass, would result in a greater energy Res. 51:279-285. flow from the plant to the nematode. A 13. NORTON, D. C., and P. HINZ. 1976. Re- greater mechanical cell destruction would lationship of Hoplolaimus galeatus and also result, and might be even more im- Pratylenchus hexincisus to reduction of corn yields in sandy soils ill Iowa. Plant Dis, Rep. portant than biomass per se. A greater 60:197-200. energy flow per unit of biomass is required 14. NORTON, D. C., and J. K. HOFFMANN. 1975. to sustain an ecosystem of lesser divers- Longidorus breviannulatus, n. sp. (Nematoda: ity, as in agrecosysterns, than o[ greater I,ongidoridae) associated wi.th stunted corn diversity, as in natural ecosystems (ll). in Iowa. J. Nematol. 7:168-171. 15. SLEDGE, E. B. 1956. Pathogenicity of the spiral Nematodes could have a greater impact on nematode, Helicotylenchus nannus Steiner, corn production in the Midwest than on 194,5, in relation to selected varieties of corn. the prairie plants that corn replaced. Data Proc. Ala. Acad. Sci. 28:123 (Abstr,). are needed on production efliciencies, de- 16. SMOLIK, J. D. 1975. Nemas. S. Dak. Farm and gree o[ cell destruction, and ratios of Home Res. 26 (fall):5-9. 17. TAYLOR, D. P. 1961. Biology and host-parasite nematode biomass relative to plant biomass relationships of the spiral nematode, Heli- in the two ecosystems. cotylenchus microlobus. Proc. Hehninthol. 166 Journal o] Nematology, Volume 10, No. 2, April 1978

Soc. "Wash. 28:60-66. 1I. Nematodes associated wi.th corn, barley, 18. TAYLOR, D. P., and E. G. SCHLEDER. 1959. oats, rye, and wheat. Plant Dis. Rep. 43:329- Nematodes associated with Minnesota crops. 333.

Influence of Low Temperature on Rate of Development of Meloidogyne incognita and M. hapla Larva@'~ T. C. VRAIN, K. R. BARKER, and G. I. HOLTZMAN ~ ,4 bstract: Development of Meloidogyne incognita and M. hapla larvae in clover roots was studied at 20, 16, 12, and 8 C in growth chambers and in the field from fall through spring, in North Carolina. Larvae of both species invaded roots and developed at 20, 16, and 12 C, but not at 8 C. The time necessary to complete the larval stages at each temperature was determined. The minimal temperature for development of M. incognita larvae was 10.08 C and 8.8 C for M. hapla larvae. In the field, soil temperature at 10 cm deep was favorable for development of larvae until the end of November, and again from February on. All stages of the nematodes survived freezing temperatures in the roots. of both species was evident in March or Apri.1 after inoculation and accumulation of 8,500 to 11,250 degree-hours. Key Words: ecology, thresh- old temperatures, survival.

The influence of temperature on the rate Tile development of M. incognita and of development of larvae of Meloidogyne M. hapla larvae was compared in this study spp. in host roots is well documented. at constant temperatures between 8 and Studies in controlled-environment cham- 20 C, and survival and development of the bers (3, 17) or in temperature-controlled larvae in the field was studied during fall water tanks in greenhouses (4, 7, 14) have and winter in North Carolina. shown that the rates of development of all stages of MeIoidogyne spp. are correlated MATERIALS AND METHODS positively with temperature between 15 and 30 C. Little work has been done to deter- Development at constant temperatures: mine the rate of development below 15 C, Ten white clover 'Dutch' (Melilotus alba) or to determine the basal temperature seedlings previously germinated on damp threshold for development. Tyler (14) paper were transplanted to 10-cm-diam pots found that an unknown species of filled with a loamy sand (texture: 82% Meloidogyne developed in tomato roots at sand, 14% silt, 4% clay). The pots were temperatures between 10 and 15 C. Griffin placed in an environmentally controlled (7) showed that Meloidogyne hapla Chit- greenhouse with a day/night temperature wood larvae penetrate alfalfa roots and regime of 22/18 C. After 5 days the seed- develop at 10 C. Hogger and Bird (8) found lings were thinned to 5 per pot and that Meloidogyne incognita (Kofoid and inoculated with Rhizobium tri[olii. White) Chitwood reproduces in the spring Depending on the subsequent tempera- in Georgia, and suggested that it may ture treatment, the plants were then develop in the roots of winter annuals in allowed to adapt and grow at decreasing fall and winter. temperatures for various periods in the environmentally controlled greenhouse or Received for publication 30 June 1977. in growth chambers (Table 1). All the Paper no. 5366 of the Journal Series of the North Carolina plants were inoculated on the same day Agricultural Experiment Station, Raleigh, N.C. 27607. Portion of the senior author's Ph.D. dissertation. with freshly hatched M. incognita or M. ZContribution no. J.669 of the Research Station, Research hapla larvae. Five ml of a suspension con- Branch, Agriculture Canada, Saint-Jean, Quebec. J3B 6Z8. SRespectively graduate student, Professor of Nematology, taining 200 larvae/ml was placed in holes Department of Plant Pathology, and Graduate Research 3-5 cm deep in the soil. The plants were Assistant, Deparlment of Biomathematics, North Carolina State University, Raleigh, N.C. 27607. The authors express then placed at their respective treatment appreciation to the personnel of the N.C. State Unit of temperatures: 20, 16, 12, or 8 C. They were Southern Plant Environment Laboratories for their as- sistance. fertilized weekly with a complete nutrient