Support of Soybean IPM in Tennessee Project R

FINAL REPORT FOR THE TENNESSEE SOYBEAN PROMOTION BOARD Support of Soybean IPM in Tennessee Project 16-26-R Scott Stewart and Jerome Grant Scott Stewart s Contribution: We continued a long term, regional study to evaluate the efficacy and value of seed treatments in soybean. The results of this tests are presented in Table 1. This test was duplicated in one or more locations in Arkansas, Mississippi, and Louisiana. The results in Tennessee were not especially noteworthy in that pest pressure was low. Although there was some increased vigor in soybean receiving an insecticide seed treatment, a significant yield response was not observed. Table 1. Summarized results of regional fungicide/insecticide/nematicide seed treatment trial done at the Research and Education Center in Milan, 2016 (Group 4.8, planted May 25). Description % Defoliation Thrips Injury Thrips Adults Thrips Total Vigor Stand Counts Yield Rating Date 6/8/2016 6/13/2016 6/14/2016 6/14/2016 6/19/2016 6/24/2016 10/5/2016 Rating Unit Percent 0-5 Scale Number Number 0-5 Scale Number Bushels Sample Size, Unit 1 Plot! Plot 5 Plants 5 Plants 1 Plot 20 RowFt 1 Acre Crop Stage Unfoliate V1 V1-V2 V1-V2 V2.5 V3 Days after Planting 14 DAP 19 DAP 20 DAP 20 DAP 25 DAP 30 DAP 133 DAP Treatment 1 Untreated 2.50 a 0.65 b 8.50 a 41.50-4.25 d 66.50-52.6-2 Trilex 2000 1.75 a 0.75 a 4.50 abc 38.25-4.28 cd 72.00-55.2-3 Trilex 2000+Poncho/Votivo 0.00 b 0.68 ab 2.25 bc 50.00-4.60 ab 70.50-55.4-4 CruiserMaxx 0.50 b 0.68 ab 1.50 c 40.00-4.55 b 77.75-55.6-5 CruiserMaxx+Avicta 0.00 b 0.48 c 2.75 bc 24.75-4.78 a 87.50-56.0-6 Intego Suite 0.75 b 0.68 ab 2.25 bc 30.00-4.48 bc 77.50-55.2-7 Acceleron 0.25 b 0.45 c 5.50 abc 31.75-4.68 ab 76.25-56.8-8 Acceleron+Poncho/Votivo 0.00 b 0.28 d 7.00 a 25.25-4.53 b 74.00-55.8-9 Trilex 2000+Aeris 0.25 b 0.35 d 6.25 ab 39.50-4.53 b 69.50-54.6 - LSD P=.05 0.8826 0.0947 4.1038 25.9445 0.2105 22.2753 5.26 Treatment Prob(F) 0.0001 0.0001 0.0158 0.5487 0.0005 0.7284 0.8956 Because of some anecdotal observations in Tennessee and other states, we investigated whether insecticide seed treatments might reduce injury caused by the application of pre-emergence herbicides. Two factorial experiments were done where herbicides were applied in a manner expected to cause crop injury. Leadoff, Fierce, or Clarity were either applied to plots where seed not were treated with insecticide or where seed were treated Gaucho or Cruiser. The results show that the herbicides caused substantial injury to seedling soybean (Table 2). Application of all herbicides at the time of planting (test 1) substantially reduced vigor, and Fierce and Clarity also reduce plant stands. All three treatments significantly reduced yield. Injury was less severe when herbicides were applied 10 days in advance of planting (test 2), with the exception of Fierce which was applied at planting. Reduced vigor was observed except with Leadoff and Fierce, and yield was

significantly lower in plots treated with Leadoff. However, we observed no interactions between herbicide and insecticide seed treatment on vigor, stand density or yield. Neither Cruiser nor Gaucho appeared to reduce injury caused by these pre-emergence herbicides. Table 2. Main effects of insecticide seed treatments and the application of pre-emergence herbicides on plant vigor and yield (variety: Schillenger 495.RC). Test 1 (planted April 25) * Test 2 (planted May 6) ** Vigor (0-5) Plants/20 RowFt Yield (B/A) Vigor (0-5) Yield (B/A) Insecticide 28 DAP 28 DAP 32 DAP Cruiser 2.688 a 96.8 a 55.7 a 3.575 a 57.7 a Gaucho 2.794 a 93.7 a 57.4 a 3.388 a 58.4 a None 2.488 a 92.4 a 57.9 a 3.469 a 58.0 a Herbicide Leadoff 1.5 oz 2.242 c 106.8 a 49.3 c 3.375 b 52.3 c Fierce 3.75 oz 2.667 b 80.0 b 58.8 b 2.583 c 56.1 bc Clarity 8 oz 1.742 d 77.8 b 53.7 bc 3.933 a 62.5 a None 3.975 a 112.7 a 66.3 a 4.017 a 61.3 ab Means followed by the same letter are not significantly different (P < 0.05). * Herbicides applied the day of planting. ** Herbicides applied 10 days before planting, except Fierce which was applied the day of planting. Both the kudzu bug and the brown marmorated stink bug (BMSB) continue to expand their range into the central and western part of the state (Fig. 1). Low but reproducing populations of BMSB have been confirmed in soybean during the last two years in Tipton, Shelby, Madison, and Giles County. Two confirmations (Tipton and Giles County) were discovered in sentinel plots established by Dr. Heather Kelly. It seems likely that BMSB is present in other areas but has not been detected. Figure 1. Known distribution of the brown marmorated stink bug in Tennessee.

Kudzu bug infestations spread dramatically in parts of Tennessee during 2016 (Fig. 2), and high populations were especially large at the WTREC in Jackson and some other areas of West Tennessee. This insect has now been confirmed in all the major soybean producing areas of the state. However, a fungus (Beauveria bassiana) was effective at controlling a large percentage of the individuals observed on both soybean and kudzu. This same phenomenon has occurred throughout the Southeast during 2015 and 2016 in areas that previously had high populations of kudzu bug. It is unclear whether kudzu bugs will continue to pose a substantial threat to soybean, or whether this threat will primarily occur along its expansion front where infection of Beauveria bassiana may be less common. Figure 2. Known distribution of the kudzu bug in United States (courtesy of www.kudzubug.org). Part of this project is to assess the appropriateness of existing or new BMPs strategies for insects that infest soybean. In 2016, insect pest populations were generally low with the exception of kudzu bugs. Thus, multiple experiments were done to assess how insecticide controls targeting kudzu bug affected yield (Table 3). It was unclear if the recommended threshold for kudzu bugs would be appropriate given the common occurrence of Beauveria bassiana fungus. In these tests, insecticide applications were either made preventatively, before kudzu bugs or other pests reached treatment level, or based on the current threshold of 25 immature kudzu bugs per 25 sweeps. Brigade or Bifenture, Karate or Warrior, Besiege, and Asana XL all provided good control of kudzu bugs in all tests (data not shown). A statistically significant yield increase was only observed in one test where maximum kudzu bug infestations exceeded the threshold by 3.1 fold. There was a trend for a 1 4 bushel/acre increase in yield (avg. 2.4) when populations of kudzu bugs where observed at levels of 0.7 2.0 times the recommended threshold. Thus, the current treatment threshold for kudzu bug worked relatively well despite the confounding effect of Beauveria

bassiana. However, these data suggest that this threshold may be too high when considering insecticide and application costs are less than $10/acre. Further testing is needed to validate this observation. Complete data for these and other trials are available at http://utcrops.com/ MultiState/MultiState.htm. Table 3. Summary of multiple trials designed to validate the recommended treatment thresholds for kudzu bugs or other insect pests on soybean. Test Maximum kudzu bugs * Other pest of note * Selected insecticide treatments Yield (B/A) 1 0.75 X Looper - 0.76 X Not treated 82.1 a Looper - 0.44 X Brigade (Automatic, Aug 2) 85.4 a 2 0.7 X None Not treated 68.2 a Brigade (R3 Automatic, July 18) 67.2 a Brigade (R5 Automatic, Aug 10) 69.8 a Brigade (Aggressive, July 13, Aug 10) 71.9 a 3 3.1 X Loopers - 0.5 X Not treated 63.5 b Loopers - 0.5 X Brigade (Threshold, Aug 2) 70.3 a 4 < 0.1 X None Not treated 52.8 a Brigade (R4 Automatic, Aug 5) 51.7 a 5 2.0 X Loopers - 0.5 X Not treated 66.6 a Loopers - 0.1 X Prevathon (Threshold, Aug 18)** 65.8 a Loopers - 0.1 X Besiege (Threshold, Aug 18) 70.3 a Loopers - 0.5 X Karate (Threshold, Aug 18) 67.4 a 6 1.1 x None Not treated 67.0 a Brigade (Threshold, Aug 2) 71.5 a Karate (Threshold, Aug 2) 69.0 a Asana XL (Threshold, Aug 2) 72.5 a 7 2.0 X None Not treated 57.5 a Bifenture (Threshold, Aug 16) 58.2 a Warrior (Threshold, Aug 16) 58.4 a Means not followed by the same letter are significantly different (P < 0.05, LSD). * X refers to relative number of kudzu bugs observed compared with the recommended treatment threshold of 25 nymphs/25 sweeps. ** Prevathon does not control kudzu bugs. Prevathon is a diamide insecticide that has provided exceptional and long residual control of caterpillar pests and is also purported to reduce tunneling caused by dectes stem borer. Working collaboratively with a graduate student from Mississippi State University, we initiated two trials to determine of applications of Prevathon would affect dectes stem borer infestations and yield. Either a single application (R3) or three applications (V6, R2, R5) were compared with plots not treated with insecticides. Too few dectes were present to determine how treatment affected dectes tunneling. Generally low insect populations were observed in these experiments, and yield was not affected by treatment (Table 4). The automatic application of Prevathon, a relatively expensive insecticide, were not cost effective in these two tests.

Table 4. The impact of automatic applications of Prevathon (14 oz/acre) on soybean yield (Pioneer P45T11R). Treatment Test 1 - Planted May 6 Yield (B/A) Test 2 - Planted May 23 Yield (B/A) Not treated 67.6 a 65.4 a Prevathon (V6, R2, R5) 67.4 a 66.9 a Prevathon (R3) 65.8 a 68.9 a Beginning in 2013, there were indications that soybean looper populations may have developed resistance to diamide insecticides (e.g., Belt SC, Besiege, Prevathon) in some geographies. Dr. Jeff Davis, LSU AgCenter, led a collaborative effort to screen population of soybean loopers for resistance. Data from laboratory assays indicated that a population from Puerto Rico collected in 2013 (PR-2013) was highly resistance to Belt SC, but populations from the southern U.S., including Tennessee, remained relatively susceptible (Table 5). Testing in 2015 indicated populations collected in Arkansas, and Mississippi Tennessee were 12.3-34.1 times more tolerant to Prevathon (chlorantraniliprole) than loopers from a known susceptible colony (Table 6). Further testing in 2016 further indicates that soybean looper populations collected across the Southeast were less susceptible to a discriminating dose of Prevathon, Belt and another insecticide class represented by Intrepid (Table 7). Soybean loopers remained susceptible to Cry1A, a Bt toxin used in foliar applications and a component of Bt cotton, Bt corn, and Bt soybean. Because soybean loopers are migratory invaders and do not overwinter in Tennessee or most of the southern U.S, it s likely that resistance to diamide is being inherited by their use in Puerto Rico, Brazil and other subtropical and tropical areas. It appears we are rapidly losing susceptibility of soybean looper to this class of chemistry. Table 5. Susceptibilty (LC50 and LC 95) of soybean looper to flubendiamide (Belt SC) in populations collected from 2012-2014. RR = resistance ratio relative to a known suscptible colony, LSU1. Courtesy of Dr. Jeff Davis (LSU AgCenter).

Table 6. Susceptibility of soybean looper to chlorantraniliprole (Prevathon) for populations collected in 2015. Colony N LC50 (ppm) Resistance ratio Arkansas 2015 * 630 33.1 34.1 Mississippi 2015 * 630 31.7 32.7 Tennessee 2015 630 11.9 12.3 Courtesy of Dr. Jeff Davis (LSU AgCenter). * Collected after application of chlorantraniliprole (Prevathon or Besiege). Table 7. Percent survival of third-instar soybean looper larvae (N = 120) to a discriminating dose of selected insecticides for populations collected from multiple states in 2016. Collection Intrepid 2F Belt SC Prevathon Cry1Ac (Foliar Bt) AL 2016 38.3 ± 2.2 25.8 ± 3.7 33.3 ± 1.7 100.0 ± 0.0 GA 2016 18.3 ± 2.2 35.8 ± 1.6 35.0 ± 2.2 99.2 ± 0.8 LA 2016 36.7 ± 2.4 42.5 ± 1.6 47.5 ± 2.1 100.0 ± 0.0 MS 2016 32.5 ± 1.6 14.2 ± 2.1 45.8 ± 3.4 100.0 ± 0.0 SC 2016 20.8 ± 2.1 40.0 ± 1.9 22.5 ± 2.5 100.0 ± 0.0 SC 2016-2 30.0 ± 1.3 22.5 ± 1.6 19.2 ± 0.8 100.0 ± 0.0 TN 2016 25.0 ± 1.7 30.0 ± 2.4 28.3 ± 0.9 100.0 ± 0.0 LSU1 (Suscep.) 95.4 ± 0.5 91.1 ± 1.3 97.2 ± 0.9 100.0 ± 0.0 Courtesy of Dr. Jeff Davis (LSU AgCenter). Jerome Grant s Contribution: 1) Ms. Kadie Britt, Department of Entomology and Plant Pathology, completed her M.S. degree (graduated August 2016). Her research focused on the kudzu bug, specifically as it relates to this funded project. Kadie s assistantship was paid partially from funding by this project and the remainder from another project. 2) Ms. Amy Michael, Department of Entomology and Plant Pathology, began her M.S. degree program in August 2016. Her research greatly expands upon the foundational research on kudzu bug in Tennessee that was completed by Kadie Britt. 3) In 2016, Kadie Britt and Amy Michael (M.S. Graduate Students in the Department of Entomology and Plant Pathology) investigated several aspects of the biology, impact, and management of the kudzu bug in Tennessee. They continued to assess its seasonality, distribution, host-plant associations, ecological interactions, and phenology, as well as better defined its overwintering sites in Tennessee. The following brief reports address each key component of their research: Seasonality, Phenology, and Overwintering Sites Populations of kudzu bug were much lower in 2016 than in 2015, possibly due to the incidence of a fungal pathogen (Beauveria bassiana) that

impacted kudzu bug populations late in 2015 (see below and Fig. 1-3). This pathogen greatly lowered the numbers of kudzu bugs entering their overwintering phase. Numerous overwintering kudzu bugs found on trees were infected with this fungus. These reductions resulted in fewer adults to infest fields in 2016. In 2015 and 2016, the kudzu bug had two generations per year in Tennessee, completing its first generation on kudzu and completing its second generation on kudzu and/or soybean. Its movement from kudzu into soybeans is dependent upon several factors (such as temperature, distance of kudzu from soybeans, and soybean planting date). Adults overwinter in multiple types of locations, but mainly in the ridges of bark on trees near kudzu fields. Early in late winter to early spring, when kudzu began to develop, kudzu bugs moved back into kudzu where they fed, mated, and reproduced. The first generation of kudzu bugs developed on kudzu, where they completed all five nymphal instars and developed into adults. If no soybean fields are nearby, kudzu bugs stay in kudzu. If soybean fields are near kudzu, these second-generation adults moved from kudzu to soybeans, where they developed through all five nymphal instars and reached the adult stage. Adults remained in soybean until crop maturity; late-season movement of kudzu bugs from soybean to kudzu was influenced by the onset of the first freezing temperatures and the maturing of soybeans. Adults then fed briefly on kudzu before moving to overwintering sites to continue the cycle described above. Cumulative degree days (i.e., heat units) were important indicators of population levels in fifth-stage instars and adults. Host-plant Associations, Distribution, and Ecological Interactions: In addition to kudzu and soybean, kudzu bug was found to feed and reproduce on two alternate host plants: bush honeysuckle and ragweed (both considered to be problematic weeds). The extent of their feeding and reproducing on these weeds, as well as the contributions of these weeds to increases of kudzu bug populations and spread into soybean, were investigated. In laboratory studies, adult kudzu bugs were active on all four plant species. Kudzu bugs, however, were more active on kudzu than on alternate host plants (soybean, bush honeysuckle, and ragweed). In no-choice experiments, ragweed was the least attractive plant species, as kudzu bugs were significantly less active on ragweed than on any other host plant. In the choice experiment, activity of insects throughout the duration of the experiment was consistently higher on kudzu and bush honeysuckle than on ragweed or soybean. The similarities of activity of kudzu bug on kudzu and bush honeysuckle, as well as the similarities of activity on soybean and ragweed, were not expected. Further studies are planned to investigate the role of these host plants in development and survival of kudzu bugs. The distribution of kudzu bug was addressed earlier in this report. Predator-Prey Relationships (Natural Enemies): Research continued to assess predator-prey relationships, especially focusing on identification of potential natural enemies of the eggs of kudzu bugs. As in 2015, no egg parasitoids were observed in 2016. However, the fungal pathogen, Beauveria bassiana (one of the most ecologically important and potentially population-reducing discoveries in 2015) was again found to be an important mortality factor of kudzu bug nymphs and adults (see Fig. 2 and 3). Infected kudzu bugs were found at all 14 study sites in six counties. At some sites, as in 2015, infection was ca. 90%+ (in other words, about 90% of the kudzu bugs at some sites were killed by this fungus). Interestingly, this fungus was still not found to infect any species other than kudzu bugs, which suggests that it may be an important management tool for kudzu bug. Although it was not found in 2014, its presence in

2015 and 2016 has greatly impacted kudzu bug populations and their impact on soybeans in Tennessee. Figure 3. The fungus Beauveria bassiana was again found to kill kudzu bug nymphs and adults in Tennessee in 2016 (white clumps are infected and dead kudzu bugs). 100 Immature % Adult % 80 Percent Infected 60 40 20 0 18 19 20 21 22 23 Week Figure 4. Incidence of Beauveria bassiana on kudzu bug nymphs and adults, Blount County, 2016.

Immature % Adult % 100 Percent Infected 80 60 40 20 0 18 19 21 22 23 Week Figure 5. Incidence of Beauveria bassiana on kudzu bug nymphs and adults, Polk County, 2016. Scientific Publications: Britt, K. 2016. An Ecological Study of the Kudzu Bug in East Tennessee: Life History, Seasonality, and Phenology. M.S. Thesis, University of Tennessee, Knoxville. 99 pp. Britt, K., C. Standish, J. Grant, and K. Vail. 2016. Invasive Pest and Fall Home Invader: Kudzu Bug. University of Tennessee Extension Publication, https://extension.tennessee.edu/ publications/documents/w358.pdf. Britt, K., J. F. Grant, G. J. Wiggins, and S. D. Stewart. 2016. Prevalence and localized impact of the entomopathogenic fungus Beauveria bassiana on kudzu bug (Megacopta cribraria) in eastern Tennessee. Journal of Entomological Science 51(4):321-324, doi: http://dx.doi.org/10.18474/ JES16-26.1. Presentations: Britt, K., J. F. Grant, S. D. Stewart, and S. D. Powell. 2016. Kudzu bug in Tennessee: Responding to a new invasive species. USDA Research Forum on Invasive Species, January 2016, Annapolis, MD (poster). Britt, K., J. F. Grant, S. Stewart, and S. D. Powell. 2015. Kudzu bug in eastern Tennessee: What s going on? Southeastern Branch, Entomological Society of America Annual Meeting, March 15-18, Biloxi, MS (poster). Britt, K., J. Grant, G. Wiggins, S. Stewart, and J. Jurat-Fuentes. 2016. Kudzu bug seasonal phenology in eastern Tennessee. Tennessee Entomological Society, October 6-7, Knoxville, TN. Michael, A., K. Britt, and J. Grant. 2016. Kudzu patch kids: The future of kudzu bug research in east Tennessee. Tennessee Entomological Society, October 6-7, Knoxville, TN.