FIELD AND FORAGE CROPS Plant Growth Stage-Specific Injury and Economic Injury Level for Verde Plant Bug, signatus (: ), on : Effect of Bloom Period of Infestation

1,2 1 3 MICHAEL J. BREWER, DARWIN J. ANDERSON, AND J. SCOTT ARMSTRONG

J. Econ. Entomol. 106(5): 2077Ð2083 (2013); DOI: http://dx.doi.org/10.1603/EC13248 ABSTRACT Verde plant bugs, Distant (Hemiptera: Miridae), were released onto caged cotton, hirsutum L., for a 1-wk period to characterize the effects of density and bloom period of infestation on cotton injury and yield in 2011 and 2012, Corpus Christi, TX. When plants were infested during early bloom (10Ð11 nodes above Þrst white ßower), a linear decline in fruit retention and boll load and a linear increase in boll injury were detected as verde plant bug infestation levels increased from an average of 0.5 to 4 bugs per plant. Lint and seed yield per plant showed a corresponding decline. Fruit retention, boll load, and yield were not affected on plants infested 1 wk later at peak bloom (8Ð9 nodes above Þrst white ßower), even though boll injury increased as infestation levels increased. Second-year testing veriÞed boll injury but not yield loss, when infestations occurred at peak bloom. Incidence of cotton boll rot, known to be associated with verde plant bug feeding, was low to modest (Ͻ1% [2012] to 12% [2011] of bolls with disease symptoms), and drought stress persisted throughout the study. Caging effect was minimal: a 10% fruit retention decline was associated with caging, and the effect was not detectable in the other mea- surements. Overall, reduced fruit retention and boll load caused by verde plant bug were important contributors to yield decline, damage potential was greatest during the early bloom period of infestation, and a simple linear response best described the yield responseÐinsect density relationship at early bloom. ConÞrmation that cotton after peak bloom was less prone to verde plant bug injury and an early bloom-speciÞc economic injury level were key Þndings that can improve integrated pest management decision-making for dryland cotton, at least under low-rainfall growing conditions.

KEY WORDS insectÐplant interaction, cotton boll injury, , plant bug

Insecticide use in cotton, Gossypium hirsutum L. (Mal- Euschistus servus (Say) (Hemiptera: Pentatomidae), vaceae), has been reduced after the success of trans- and southern green stink bug, Nezara viridula (L.) genic Bt (Bacillus thuringiensis) cotton and area-wide (Hemiptera: Pentatomidae) (Willrich Siebert et al. eradication of boll weevil, Anthonomous grandis gran- 2005, Medrano et al. 2009). For the verde plant bug, dis Boheman (Coleoptera: Curculionidae) (Edge et Armstrong et al. (2013) showed that bolls Ͻ2.7 cm in al. 2001, Allen 2008). These advances have likely re- diameter (equates to about Ͻ166 degree days [DD] leased the sucking bug complex of stink bugs and plant [15.6ЊC base] or Ͻ12-d-old from the Þrst day of bloom bugs (Hemiptera: Pentatomidae and Miridae) from [white ßower]) were readily injured, whereas older indirect insecticide control (Lu et al. 2010). Associ- bolls incurred little injury in a no-choice test. When ated cotton boll damage caused by stink bug feeding given a choice of varied-age squares and bolls occur- has increased during the past 2 decades (Greene et al. ring along a branch, Brewer et al. (2012a) found that 2001), and verde plant bug, Creontiades signatus Dis- verde plant bug injury of large squares and young tant (Hemiptera: Miridae), has caused similar damage bolls, both within a few days of white ßower, led to to cotton in South Texas (Armstrong et al. 2010). increased boll abscission and subsequent yield reduc- In response, insecticide use guidelines have been tion. Khan et al. (2006) also noted that a mirid relative, developed for this sucking bug species complex. Boll (Stal), was most damaging when sensitivity to feeding formed the basis for recommend- feeding on prebloom squaring and early bloom cotton ing inspection of selected sizes of green bolls for in- in Australia. In a 2-yr survey of commercial Þelds in ternal feeding symptoms caused by brown stink bug, South Texas (Brewer et al. 2012c), lint and seed deg- radation and associated cotton boll rot development, 1 Texas A&M AgriLife Research and Department of Entomology, caused by bacterial contamination of the boll during Texas A&M AgriLife Research and Extension Center, 10345 State insect feeding (Medrano et al. 2009), were seen in Highway 44, Corpus Christi, TX 78406. 2 Corresponding author, e-mail: [email protected]. verde plant bug-infested Þelds. Abundance and sea- 3 USDAÐARS, 1301 N. Western Rd., Stillwater, OK 74075. sonal occurrence of verde plant bug varied substan-

0022-0493/13/2077Ð2083$04.00/0 ᭧ 2013 Entomological Society of America 2078 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 5 tially, reßecting a possible yield responseÐinsect den- after cotton emergence of the previous year (week 1Ð2 sity relationship that was sensitive to when verde plant of bloom), but at a cotton physiological age that more bug infested cotton. closely matched the peak bloom period of the previous Based on these past studies, we hypothesized that year (8Ð9 nodes above Þrst white ßower). Acceler- infestations were more injurious and yield declined as ated plant development in 2012 was likely associated verde plant bug density increased and as verde plant with drought conditions (see Results), and a second bug occurred earlier in bloom. Here, several densities later period of infestation was not attempted. The of verde plant bug were placed on cotton during early infestation rates were replicated Þve times in a ran- and peak bloom to characterize possible plant growth domized complete block. A no-cage control was not stage-speciÞc yield response-insect density relation- included based on results of the previous year. ships. These relationships were used to identify the Adult verde plant bugs used for infesting cages were period of bloom less prone to verde plant bug injury obtained from Þeld-collected and a laboratory and develop an economic injury level (EIL) sensitive colony frequently supplemented with Þeld-collected to cotton development stage (Pedigo et al. 1986, Bene- insects from several wild and cultivated host plants, dict et al. 1989). including cotton and several seepweeds, Suaeda spp. (Chenopodiaceae) (Armstrong 2010). The insects Methods and Materials were held without food overnight before infestation. Two days before each infestation date, plants were Protocol for Varying Verde Plant Bug Density at caged and sprayed with short-residual pyrethrins Early and Peak Bloom. Verde plant bugs were re- (0.02% by volume, United Industries, St. Louis, MO). leased into caged cotton for a 1-wk period to charac- Furthermore, periodic inspection of the surrounding terize the effects of insect density and bloom period cotton showed negligible boll injury. Plants were of infestation on cotton injury and yield in 2011 and treated with zeta-cypermethrin (FMC, Philadelphia, 2012, Corpus Christi, TX. FiberMax 840 RRB2 cotton PA) on day 8 postinfestation and again on day 14 to seed (Bayer CropScience, Research Triangle Park, reduce the chance of other insects and remnant verde NC) was planted in early April on 91-m rows and Ϸ plant bug contaminating the caged cotton. The cages 96-cm row centers at a Þeld site of 0.4 ha, resulting remained in place until harvest. in a plant stand of Ϸ77,800 plants/ha (31,500 plants per Plant Injury and Yield. The experimental plants acre). The crop was grown under dry land conditions, were harvested by hand on 9 August (94 d postemer- no insecticides were applied to the Þeld, and normal gence) in 2011 and 15 August (107 d postemergence) agronomic practices for the region were used (Mor- in 2012. Individual plants of each cage were mapped gan 2011). for fruit retention by using the computer program In 2011, groups of four whole cotton plants enclosed PMAP (Landivar and Benedict 1996). Mean percent by large organza fabric cages (107 by 152 cm) were infested with verde plant bugs at early (10 June) fruit retention per plant was calculated for sympodia bloom stage and 1 wk later as plants were approaching branches 1Ð5 (bottom branches), 6Ð10 (middle peak bloom. Early bloom was characterized as wk 1Ð2 branches), and 11Ð15 (top branches) for each treat- of bloom and 10Ð11 nodes above Þrst white ßower on ment. This calculation produced a boll health evalu- fruiting position one from the main stem (Þrst white ation averaged over all positions from the main stem, ßower; Kerby et al. 2010), and peak bloom was char- in contrast to higher square retention averages for the acterized as Ϸ8Ð9 nodes above Þrst white ßower. Þrst fruiting position used in other programs for mon- Cages were infested with adult verde plant bugs at itoring crop development (Oosterhuis and Bourland rates of 0, 0.5, 1, 2, and 4 adult verde plant bugs per 2008). Green and open bolls retained on the plant plant (i.e., 0, 2, 4, 8, and 16 bugs per cage, respectively) were counted, rated for injury by using a 0Ð4 scale, for 7 d. These rates were based on density estimates of and scored for presence of symptoms of cotton boll verde plant bug associated with boll injury and eco- rot. The boll injury scale ranged from 0 (representing nomic damage in commercial Þelds (Brewer et al. no injury) to 1Ð3 (representing a progression of lint 2012c). The 7-d infestation period was used to reßect and seed degradation occurring in one to three loc- a commercial Þeld setting during which verde plant ules, respectively) to 4 (representing severe degrada- bug may remain undetected between weekly insect tion of lint and seed in all locules) (Lei et al. 2003). The scouting. The infestation rate and plant growth stage boll interior was thoroughly inspected for symptoms treatment combinations were arranged in a factorial of cotton boll rot caused by bacteria (Medrano et al. design set out in a randomized complete block of six 2009). Mean boll injury score and percentage of bolls replications. An open-Þeld noninfested group of four with cotton boll rot for each treatment were catego- plants (no-cage control) was established as an addi- rized by vertical section of the plant, which approxi- tional treatment to test for caging effect. In 2012, mated the three sympodia branch categories used for infestations were adjusted to 0, 0.125, 0.25, 0.5, 1, and the fruit retention measurement (i.e., top, middle, and 2 verde plant bugs per plant to further characterize bottom branches). To obtain seed and lint weight, plant responses seen at the low verde plant bug den- seed cotton was ginned by using a 10-saw laboratory sities used in 2011. Eight plants per cage were used to cotton gin (Continental Eagle Corp., Prattville, AL). accommodate infesting at the lower rates. In 2012, Weights were recorded per plant and converted to a plants were infested on 28 June during the same week hectare basis. October 2013 BREWER ET AL.: VERDE PLANT BUG ON COTTON:INJURY AND YIELD RESPONSE 2079

Data Analysis and EIL Calculation. To assess overall cage effects, fruit retention, boll count, lint weight, and seed weight of the additional no-cage control were compared with the same measures from the caged noninfested control in 2011. Analysis of vari- ance (ANOVA) was used, conforming to a two (un- caged control and caged control) by two (plant growth) factorial (Littell et al. 1991). All measurements taken from the cages (deleting the no-cage control data) were used to explore treat- ment effects by using ANOVA for a two-way factorial (plant growth and infestation rate) in a randomized block design in 2011, and the randomized block design of one main factor (infestation rate) in 2012. Boll count data were transformed by the square root of (count ϩ 0.5). The arcsine square-root transformation was used for the percentage of fruit retention and bolls with symptoms of cotton boll rot. ANOVAs were used for the whole-plant measures and plant sections when measures were taken. In 2011, a mixed effects model was used where plant growth stage was Þxed, infes- tation rate was random, and the interaction was used as the error term for the main effects. If the interaction was signiÞcant (P Ͻ 0.05), the infestation rate effect Fig. 1. Fruit retention in middle branches when caged (Þve rates) was assessed with linear, quadratic, and plants were infested at early bloom and peak bloom with 0Ð4 cubic contrasts separately for the two plant growth adult verde plant bugs per plant in 2011 (A) and peak bloom stages by slicing the data by plant growth stage (Littell at infestation rates of 0Ð2 bugs per plant in 2012 (B). Infes- et al. 1991). If the interaction was not signiÞcant, the tation duration was 1 wk. A noninfested open-Þeld treatment same contrasts were used for a signiÞcant infestation (uncaged) was included in 2011. Lines above bars are SEMs. rate main effect. In 2012, the trend analyses were done with linear, quadratic, and cubic contrasts appropriate Results and Discussion for the six infestation rates. Regression analyses using Þrst (simple linear), sec- Influence of Caging and Growing Conditions. ond (quadratic), and third (cubic) order regression There was lower fruit retention in the cages compared equations (Neter et al. 1985, Littell et al. 1991) were with the no-cage control (ranging from 6 to 12% used to describe yield responseÐinsect density rela- lower), with a detectable effect seen only when caging tionships for signiÞcant contrasts of the lint weight occurred early bloom (plant growthÐcage interaction: measurement. Equations were estimated separately F ϭ 5.6; df ϭ 1, 15; P ϭ 0.034) (Fig. 1A). Differences for the two bloom infestation periods or as a common in boll count and yield measures were not detected regression, depending on the signiÞcance of the plant (P Ͼ 0.10), and treatment effects were much more growthÐinfestation rate interaction. For linear rela- predominant (see Results). Predator exclusion by cag- tionships, y ϭ mxϩ b, where y was the yield response ing was not observed, likely because of the short 7-d in lint weight per plant, x was the insect density in bugs infestation period and limited predation as seen in the per plant, b was the y-intercept, and m was the slope surrounding Þeld, including lack of red imported Þre in lint weight (plant basis) per bug per plant. An EIL ant, Solenopsis invicta Buren (Hymenoptera: Formi- was calculated by using the formula of Pedigo et al. cidae), at this site (M.J.B., personal observation). Lint ϭ (1986) for each blooming period (i): EILi yield in the caged uninfested controls were average to C/(V*Ii*Di*K), where C was expected cost of control, high compared with historical yield records for the V was the expected market value of the cotton lint, and region (Chen and Miranda 2008), likely because of the K was the expected proportion of the insect popula- efÞciencies in hand-harvesting despite anticipated in- tion controlled, set as constants of US$18.53/ha ßuences of drought conditions. Drought was severe (US$7.50 per acre), US$1.90/kg (US$0.86 per lb), and during the study: 7.6 and 15.1 cm of rainfall occurred

0.9, respectively. Ii was plant injury per insect, and Di April through August in 2011 and 2012, respectively, was yield loss per plant injury unit for each blooming compared with 45.7 cm in 2010 and a 35.5 cm average period (i). Lint weight loss per bug per plant from the over 125 yr (Corpus Christi station; National Weather experiment was used to estimate the product Ii*Di, Service 2012). These results and observations sup- and the much lower-valued seed weight loss was not ported the conclusion of negligible complications in included. Because only signiÞcant plant growthÐin- data interpretation because of caging, and of applica- festation rate linear relationships were detected, Ii*Di bility of the results to dry land cotton, at least under was estimated from the slope m, converted to lint low-rainfall growing conditions. weight (hectare basis) per bug per plant by using a Fruit Retention and Subsequent Boll Count. In conversion factor of 77,800 plants per hectare. 2011, fruit retention differed among treatments in the 2080 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 5

Fig. 3. Boll injury (0Ð4 scale) in middle (A) and bottom (B) branches when caged plants were infested at early bloom and peak bloom with 0Ð4 adult verde plant bugs per plant in 2011. Infestation duration was 1 wk. A noninfested open-Þeld treatment (uncaged) was included. Lines above bars are SEMs.

at early bloom (F ϭ 8.66; df ϭ 1, 20; P ϭ 0.008), whereas no differences were evident when plants were infested during peak bloom (P Ͼ 0.35) (Fig. 2B). This middle boll count reduction corresponded to low Fig. 2. Number of green and open bolls in top (A), fruit retention occurring on middle branches when middle (B), and bottom (C) branches when caged plants were infested at early bloom and peak bloom with 0Ð4 adult infestations occurred early bloom (Fig. 1A). For top verde plant bugs per plant in 2011. Infestation duration was and bottom branches, a similar interaction was seen 1 wk. A noninfested open-Þeld treatment (uncaged) was (top bolls, F ϭ 3.47; df ϭ 4, 44; P ϭ 0.010; bottom bolls, included. Lines above bars are SEMs. F ϭ 2.96; df ϭ 4, 44; P ϭ 0.030), with boll counts declining as infestation rates increased when infesting plants at early bloom (linear contrast: top bolls, F ϭ middle branches (plant growthÐinfestation rate inter- 7.92; df ϭ 1, 20; P ϭ 0.01; bottom bolls, F ϭ 4.57; df ϭ action: F ϭ 2.83; df ϭ 4, 44; P ϭ 0.036) (Fig. 1A). Fruit 1, 19; P ϭ 0.045) (Fig. 2A and C). In 2012, boll count retention decreased as infestation rate increased dur- did not differ across infestation rates for the whole ing the early bloom infestation (linear contrast: F ϭ plant, ranging between 6.3 Ϯ 0.8 (SEM) and 7.2 Ϯ 0.6 13.47; df ϭ 1, 20; P ϭ 0.0015), but a fruit retention bolls per plant (P Ͼ 0.60). Boll load in 2012 was less decline was not evident when infesting the plants later than half of the load occurring in 2011, likely because at peak bloom (P ϭ 0.44) (Fig. 1A). No curvilinear of the second consecutive year of drought. effects were detected (P Ͼ 0.07). For top and bottom Boll Injury and Cotton Boll Rot. Differences in branches, no signiÞcant differences in fruit retention injury of retained bolls were detected in the middle were detected (interaction and infestation rate main and bottom branches in 2011. A plant growth stageÐ effect, P Ͼ 0.05). In 2012, fruit retention for all sym- infestation rate interaction was not detected (P ϭ podia branches did not differ across infestation rates 0.90), but middle boll injury increased in a linear (P Ͼ 0.30) (Fig. 1B). Very similar retention rates fashion as infestation rate increased for both infesta- occurred both years for the peak bloom period (Fig. tion periods (F ϭ 27.6; df ϭ 1, 44; P ϭ 0.004) (Fig. 3A). 1A and B). A similar treatment effect was seen on the bottom Separating the plant vertically into thirds, a signif- branches: no interaction was detected (P ϭ 0.44), and icant plant growth stageÐinfestation rate interaction boll injury increased as infestation rate increased for was detected when counting middle-branch bolls (F ϭ both infestation periods (linear contrast: F ϭ 19.85 3.21; df ϭ 4, 44; P ϭ 0.022) (Fig. 2B). Boll count in the df ϭ 1, 44; P ϭ 0.012) (Fig. 4B). Injury to bottom bolls middle third of the plant decreased in a linear fashion was lower than injury to middle bolls (Fig. 4A and B). as the infestation increased when plants were infested Boll injury in 2012 also increased linearly across in- October 2013 BREWER ET AL.: VERDE PLANT BUG ON COTTON:INJURY AND YIELD RESPONSE 2081

Fig. 5. Percentage of bolls with symptoms of cotton boll rot from bottom branches when caged plants were infested at early bloom and peak bloom with 0Ð4 adult verde plant bugs per plant in 2011. Infestation duration was 1 wk. A noninfested open-Þeld treatment (uncaged) was included. Lines above bars are SEMs.

study was lower than detected in a previous survey in South Texas (Brewer et al. 2012c). The highest inci- dence of cotton boll rot in the current study (12%) was Ϸ10% lower than the highest levels seen in the 2010 survey, when infestations of Ϸ0.3 verde plant bugs per plant were encountered in the Þelds with economic damage (Brewer et al. 2012c). As 2010 was a relatively wet year followed by two consecutive years of drought with associated low humidity, there may be an impor- tant environmental factor associated with the rela- Fig. 4. Boll injury (0Ð4 scale) in middle (A) and bottom tively low cotton boll rot detected in 2011 and 2012 (B) branches when caged plants were infested peak bloom (Baga 1970). with 0Ð2 adult verde plant bugs per plant in 2012. Infestation Yield Response. SigniÞcant plant growthÐinfesta- duration was 1 wk. Lines above bars are SEMs. tion rate interactions were detected for both lint and seed weight per plant in 2011 (F Ͼ 2.6; df ϭ 4, 44; P Ͻ festation rates in the middle (F ϭ 7.74; df ϭ 1, 20; P ϭ 0.05). When infested at early bloom, lint weight per 0.011) (Fig. 3A) and bottom (F ϭ 5.91; df ϭ 1, 20; P ϭ plant (F ϭ 5.08; df ϭ 1, 20; P ϭ 0.036) (Fig. 6A) and 0.025) (Fig. 3B) portion of the plant. Overall, retained seed weight per plant (F ϭ 5.69; df ϭ 1, 20; P ϭ 0.027) bolls were susceptible to verde plant bug feeding, and (Fig. 6B) declined in a linear fashion as infestations the relatively smaller bolls (in the middle of the plant) increased from 0.5 to 4 bugs per plant. No curvilinear were injured more than the relatively larger bolls trends were detected (P Ͼ 0.16). Plants infested at found lower in the plant. These results were consistent peak bloom had no detectable differences for the yield with previous reports of smaller bolls incurring more measures across infestation rates (P Ͼ 0.13) (Fig. 6A injury than older bolls (Brewer et al. 2012a, Armstrong and B). Reanalyzing the yield on a per-boll basis, there et al. 2013). On top branches, boll injury on retained were no signiÞcant differences in lint or seed weight bolls was not seen while boll load declined as verde per boll (plant growthÐinfestation rate interaction and plant bug infestations increased. This likely reßected infestation rate main effect: P Ͼ 0.15) (data not high abscission of squares and small bolls at the top of shown). In addition, the linear decline in fruit reten- the plant, leading to fewer retained bolls (Fig. 2A) tion and boll load as infestation rates increased (Figs. with less injury. 1 and 2) supported an interpretation that the main When visually inspecting open bolls at harvest, up contributor to yield decline was poor fruit retention to 12% of bolls had symptoms of cotton boll rot in 2011, caused by verde plant bug feeding during early bloom. and treatment differences in cotton boll rot were seen In 2012, lint weight (ranging between 12.0 Ϯ 0.08 on bottom bolls (Fig. 5). A plant growthÐinfestation [SEM] and 13.4 Ϯ 0.4 g per plant) and seed weight rate interaction was not detected (P ϭ 0.73), but there (ranging between 20.1 Ϯ 1.5 and 22.5 Ϯ 0.08 g per was a linear increase in cotton boll rot as infestation plant) did not differ across infestation rates (P Ͼ 0.60), rates increased for both infestation periods (F ϭ 28.4; similar to the peak bloom infestation period in 2011. df ϭ 1, 32; P ϭ 0.006) (Fig. 5). Cotton boll rot detec- Yields in 2012 controls were about half those seen in tions were concentrated in bottom branches, where a 2011, likely because of depletion of subsurface soil more favorable microhabitat for cotton boll rot de- moisture caused by the second consecutive year of velopment may have been present. No treatment dif- drought. ferences were detected in 2012 (P Ͼ 0.30), and cotton The signiÞcant yield loss per bug during early bloom boll rot detections were rare (Ͻ1% of bolls with symp- corresponded with previous Þndings that verde plant toms). We note that cotton boll rot prevalence in this bug feeding on small bolls and large squares resulted 2082 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 5

proposed for verde plant bug (Brewer et al. 2012b); therefore, an adjusted EIL of 0.22 verde plant bug per plant should be considered for Þeld monitoring pur- poses by using beat bucket sampling. This EIL was consistent with Þeld observations of economic damage associated with verde plant bug densities Ͼ0.3 bugs per plant during a Þeld survey of commercial Þelds in South Texas, 2010 (Brewer et al. 2012c). The Þeld survey and cage study spanned 3 yr, bridging across good soil moisture to drought condi- tions. Nevertheless, yield loss may need to be adjusted upward and the EIL lowered under growing condi- tions more favorable to cotton boll injury, including cotton boll rot disease. Additional yield loss is plausi- ble under conditions of greater rainfall and humidity that is conducive to cotton boll rot disease develop- ment (Baga 1970) that may exceed the 12% peak incidence of cotton boll rot seen in this study. Con- sidering related species, in-Þeld spray trials, and cag- ing studies, yield declined when infestations of 1Ð3 C. dilutus per m-row occurred in early bloom cotton in Australia (Khan et al. 2006). By using the 77,800 Fig. 6. Lint (A) and seed (B) weight per plant (per plants/ha conversion factor and 96-cm row spacing, hectare given on right axis) when caged plants were infested our Þeld-monitored EIL of 0.22 verde plant bug per at early bloom and peak bloom with 0Ð4 adult verde plant plant converts to 1.65 verde plant bugs per m-row, bugs per plant in 2011. Infestation duration was 1 wk. A whereas our EIL directly from the cage study converts noninfested open-Þeld treatment (uncaged) was included. to 3.30 verde plant bugs per m-row. Given potential Lines above bars are SEMs. difference in speciesÐcotton variety interactions, thresholds for the two species appeared to be similar or differed modestly. in higher boll abscission than when feeding occurred For integrated pest management decision-making, on larger bolls (Brewer et al. 2012a). Declines in fruit biological (e.g., verde plant bug movement) and en- retention, boll load, and yield loss were not detectable vironmental (e.g., drought relationship to cotton boll in plants infested later in bloom, even though boll rot) considerations likely warrant some form of con- injury and cotton boll rot increased as infestation rates tinued inspection of internal damage of green bolls increased at both infestation periods. These results (Medrano et al. 2009, Brewer et al. 2012c). ReayÐJones were consistent with damage assessments of the mirid et al. (2010) noted these factors when advising green C. dilutus on cotton in Australia (Khan et al. 2006). boll inspection as the preferred method of considering The apparent lower contribution of boll injury and damage potential from stink bug species. Given the associated cotton boll rot to yield decline may be ease in sampling for verde plant bug (Brewer et al. linked to the drought conditions experienced in this 2012b) and an EIL for Þeld monitoring (0.22 verde cage study, as previously noted. Overall, reduced fruit plant bug per plant) calculated in this study, combined retention and boll load caused by verde plant bug use of verde plant bug sampling and green boll in- were important contributors to yield decline, damage spection may be a viable option (Brewer et al. 2013). potential was greatest during the early bloom period ConÞrmation that cotton after peak bloom was less of infestation, and a simple linear response best de- scribed the yield responseÐinsect density relationship. prone to verde plant bug injury and an early bloom- EIL and Integrated Pest Management Decision- speciÞc EIL were key Þndings that can improve in- Making. Calculation of an EIL was appropriate for tegrated pest management decision-making for dry early bloom infestations. By using data from the sig- land cotton, at least under low-rainfall growing con- niÞcant linear contrast for the lint measure for the ditions. early bloom infestation, the regression was y ϭϪ0.31 x ϩ 21.9, R2 ϭ 0.47, with the slope equating to a lint yield loss of 0.31 g of lint (plant basis) per bug per Acknowledgments plant. For the EIL calculation, the slope was converted We thank J. Martinez and C. Farias for providing Þeld and to an Ii*Di of 24.12 kg of lint loss (hectare basis) per bug per plant, by using the 77,800 plants/ha conver- other technical support. Many thanks to the Texas A&M AgriLife Research and Extension Center, Corpus Christi, for sion factor. Setting C, V, and K as constants (US$18.53/ provided land management support. The reviews of G. Me- ha, US$1.90/kg, and 0.9, respectively), the EIL from drano (U.S. Department of AgricultureÐAgriculture Re- the cage study was calculated at 0.45 verde plant bug search Services), G. Odvody, and R. Parker (Texas A&M per plant for early bloom infestations. Beat bucket AgriLife Research) on an earlier version are greatly appre- sampling with a Ϸ50% sampling efÞciency has been ciated. This work was partially supported by a Texas State October 2013 BREWER ET AL.: VERDE PLANT BUG ON COTTON:INJURY AND YIELD RESPONSE 2083

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