Foliar applied insecticides, application rates, and application timings for the control of the Soybean Aphid insecticide (2016)

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1 Foliar applied insecticides, application rates, and application timings for the control of the Soybean Aphid insecticide (2016) Bruce Potter, University of Minnesota Extension IPM Specialist Travis Vollmer, Plot Technician University of Minnesota Southwest Research and Outreach Center Summary During 2016, several foliar applied insecticides, application rates and application timings were evaluated for control of the soybean aphid, Aphis glycines Matsamura (SBA) at the University of Minnesota Southwest Research and Outreach Center near Lamberton, MN. The pyrethroid insecticide, lambdacyhalothrin (Warrior II), the sulfoximine insecticide, sulfoxaflor (Transform), a Transform tank mix with the fungicide premix fluxapyroxad plus pyraclostrobin (Priaxor), were applied as an early, prophylactic application to R2 stage soybeans on July 19. The same compounds, an additional rate of lamdacyhalothrin, the pyrethroid + neonicitinoid insecticide mix containing lamda-cyhalothrin + thiomethoxam (Endigo ZC), two rates of the pyrethroid insecticide, bifenthrin (Brigade 2EC), and Priaxor alone were also applied to R4 stage soybeans on August 10. The pesticide treatments and timings were compared to a control (water only) for their effect on soybean aphid populations and soybean yield. The SBA population was less than 1 aphid/plant on July 19 and approximately 92 aphids/plant with immigrating alate aphids on August 10. The latter treatment was applied before the economic threshold/august 15 target because of weather and labor concerns. By August 12, twenty-four days after application, the R2 application of 1.6 fl. oz. of Warrior II contained as many or more soybean aphids as the R4 fungicide alone or untreated control treatments. This relationship continued for the remainder of the experiment. The fungicide treatment alone showed a temporary reduction in SBA populations 7 DAT. The R2 Warrior II, R4 Priaxor and control treatments had more cumulative aphid-days than treatments containing an insecticide over the period of the trial. Endigo ZC, the two R4 treatments containing Transform and the 2.1 fl. oz. rate of Brigade accumulated the fewest aphid-days. Treatments with fungicide yielded more than those without except for the high rates of Warrior II and Brigade. The addition of Transform insecticide to the Priaxor fungicide did not result in more soybean yield. The early Warrior application, the late Transform application and the low rates of Warrior II and Brigade were lowest yielding and equivalent to the pesticide-free control. Background The soybean aphid, Aphis glycines Matsumura (SBA), is the insect pest most consistently damaging to Minnesota soybeans. Southwest Minnesota has had populations of SBA reaching the 250 aphids/plant economic threshold every growing season since the 2003 growing season with SBA populations varying in distribution and severity each year. Until the 2015 growing season, insecticide performance issues were rarely reported. Aphids collected from 2015 field-scale insecticide failures near the location of this study were documented to be resistant to synthetic pyrethroid insecticides (Group 3a) by laboratory bioassays during This trial was designed to look at aphid control and resultant yield differences between insecticide products

2 belonging to the Group 3a, sulfoxamine (4c) and neonicitinoid (4a) insecticides. Both low and high label rates of two Group 3a insecticides were included as an indicator of reduced SBA susceptibility to the insecticide. Methods This trial was located at the University of Minnesota, Southwest Research and Outreach Center, Lamberton, MN. Site, information on the site, experimental design, treatments, and application methods are presented in Table 1. The growing season was characterized by moderate temperatures, timely, above-normal rainfall and exceptional yields. Weather details can be found at The trial was placed within a field of Pioneer 22T69 soybeans planted May 1 with a sixrow, 30-inch row space planter (John Deere 7200 Max Emerge II, John Deere, Moline, IL). Alleys between replicate blocks were cut into the bulk planted field with a 55-inch wide rotary tiller (John Deere 655, John Deere, Moline, IL) the day before the first insecticide application timing. Insecticides and fungicides were evaluated in a randomized block design with four replications. Insecticide applications were made using a two-man boom sprayer pressurized with C02 (R&D Sprayers, Opelousas, LA) spraying the center four rows of each six-row plot. This design protected against fine spray particle drift between plots and left a running check on each side of a plot. Eight (8) TeeJet 8001XR nozzles (TeeJet Technologies) placed on 15-inch centers applied 15 gallons/acre water at approximately 35 PSI. Additional application, agronomic and site environmental and application information are given in Table 1. In some cases, log 10 transformations of data were needed to satisfy ANOVA assumptions. Mean separations (p= 0.05) based on log transformed data are provided where appropriate. July 19 pesticide applications to R2 stage soybean consisted of the following products and per acre rates: Warrior II insecticide at 1.6 fl. oz., Transform insecticide at 0.75 oz., Transform insecticide at 0.75 oz. plus Priaxor fungicide at 4 fl. oz. These treatments were included to evaluate duration of SBA control. August 10 pesticide treatments to R4 stage soybeans consisted of the following products and per acre rates: Brigade 2EC insecticide at 2.1 fl. oz. and 6.4 fl. oz., Warrior II Insecticide at 0.96 fl. oz. and 1.6 fl. oz., Transform insecticide at 0.75 oz., Transform insecticide at 0.75 oz. plus Priaxor fungicide at 4 fl. oz., Priaxor fungicide at 4 fl. oz., Endigo ZC insecticide at 3.75 fl. oz. The untreated control consisted of water alone at both application timings. The latter treatments were included to compare insecticide efficacy and to evaluate rate responses of the pyrethroid insecticides on SBA populations at the 250 SBA/plant economic threshold.

3 To reduce the chance of contamination during, the water control and fungicide only treatments were applied before treatments containing insecticide and the boom and nozzles were rinsed with water between products. Aphid populations at a given sample period were assessed as aphids counted on a whole plant and based on a sample of five plants for each plot. Yields were taken from the center two rows of each plot using a plot combine (ALMACO, Nevada, IA) and adjusted to 13% moisture. Results and discussion The July 19, R2 soybean stage treatments were applied to very low SBA populations of less than 1 aphid/plant. The August 10, R4 applications were applied to SBA populations much less than the intended 250 SBA/plant threshold population. A forecast rain event combined with expected late-season labor shortages drove the decision for the early application. The August 10 treatment was made to SBA populations averaging 92/plant (based on samples of randomly selected untreated plots - data not shown) that were rapidly increasing and with significant immigration of alates occurring. Aphid control and yield results by treatment are presented in Table 2. Aphid populations over time for several of the insecticide treatments are illustrated in Figure 1. On August 8, two days before the R4 pesticide treatments were applied, the R2 treatments containing Transform had significantly fewer aphids. Although the R2 timing of 1.6 fl. oz. of Warrior II had fewer aphid initially, August 8 (20 DAT-1), SBA populations were similar to treatments without an insecticide applied. By August 12 (24 DAT-1), the 1.6 fl. oz. rate of Warrior II still had SBA populations as high as the Priaxor fungicide alone and no-pesticide control. Populations in the R2 Warrior II treatment remained as high or higher than the no-pesticide control for the remainder of the trial. The R2 Transform treatments remained below the R2 Warrior II, the R4 Priaxor alone, and the no-pesticide control. However, two days after the R4 timing, the early Transform applications had more aphids than the R4 Endigo ZC and 2.1 oz. of Brigade EC treatments. By August 17, or within seven days of the R4 insecticide application (7 DAT-2), SBA populations within the no-pesticide control had passed the 250 SBA/plant threshold; they continued to increase until August 31, declining thereafter from lower leaf senescence and fungal entomopathogens. At the 7 DAT-2 timing, fungicide alone had fewer aphids than the no-pesticide control but this reduction was no longer present by 14 DAT-2. At the August 25 th sampling, the R2 Transform applications had more aphids than R4 insecticide applications with the exception of the 0.96 oz. rate of Warrior II and 6.40 oz. rate of Brigade 2EC. Over the period of the trial, the R2 Warrior II, the R4 Priaxor, and control treatments had greater SBA population densities as estimated by cumulative aphid-days (CADs) than

4 treatments containing an insecticide. Endigo ZC, the two R4 treatments containing Transform and the 2.1 fl. oz. rate of Brigade accumulated the fewest aphid - days. Yields generally followed SBA population density (Figure 2). Treatments with fungicide yielded more than those without except for the high rates of Warrior II and Brigade; the addition of Transform insecticide to the fungicide did not further increase soybean yield. Septoria brown spot, Septoria glycines, was the most prevalent foliar soybean disease causing minor late-season lower leaf senescence. The early Warrior II application, the late Transform application and the low rates of Warrior II and Brigade were lowest yielding and equivalent to the pesticide-free control. There was not a significant yield benefit for R4 insecticide application compared to the no-pesticide control. There was not a significant rate response for either Warrior II or Brigade 2EC. These data illustrate the potential for increased SBA populations and soybean yield reduction with early, prophylactic insecticide applications. They lend support to published date on SBA economic injury level (EIL) and maintaining a 250 aphid/plant economic threshold (ET). Table 1. Site and Application Information County: Redwood, MN Nearest town: Lamberton, MN Soil type: Normania loam Fertility: Soil test values (2013) 45 ppm P 182 ppm K 6.2 ph 4.8 % O.M. Previous Crop: 2014 Soybean, 2015 Corn Tillage: Fall 2015, Mulch Ripper; Spring 2016, Field cultivator Row spacing: 30 Cultivar: Pioneer P22T69 Seeding rate: 160,000 seeds/acre planted 1.5 deep into a dry seedbed Planting date: May 20, 2016 Weed control: Pre None Post Cornerstone Plus 36 fl oz 6/17/16 Post Cornerstone Plus 36 fl oz plus Fusilade 3 fl oz 7/5/16 Harvested: October 14, 2016 Design: Randomized complete block with 4 replications Plot size: 15 x 30 - The center 4 of 6 rows (10 ) were treated, the center 2 of 6 rows were sampled for aphid populations and harvested for yield. Application information: Date: July 19, 2016 August 10, 2016 Temperature: 75 F 88 F RH: 91% 80 % DP: 70 F 73 F Wind conditions: 9 mph 12 mph Crop stage at application: R2 R4 Crop height at application: 22 inches 41 inches Insecticide treatments were applied with a two-man, 8 nozzle boom sprayer (R&D Sprayers), 8001 flat fan nozzles on 15-inch spacing, 15 gallons/acre and 35 PSI pressure with boom 18 above soybean canopy.

5 Pesticide compounds used in this study Priaxor fungicide BASF Corporation fluxapyroxad plus pyraclostrobin Carboximide (7) plus Strobilurin (11) Brigade 2EC insecticide FMC Corporation bifenthrin Synthetic pyrethroid (3A) Endigo ZC insecticide Syngenta Crop Protection, Inc. lambda-cyhalothrin + thiomethoxam Synthetic pyrethroid (3A) + Neonicitinoid (4A) Warrior II with Zeon Technology insecticide Syngenta Crop Protection, Inc. lambda-cyhalothrin Synthetic pyrethroid (3A) Transform WG insecticide Dow AgroSciences sulfoxaflor Sulfoxamine (4C) Acknowledgments This trial was supported in part by funding from Dow Ago Sciences and the Minnesota Soybean Research and Promotion Council. Thanks to Jacob Samuelson, Josh Christoffer, and Kegan Zimmerman for help with this study. The information given in this publication is for educational purposes only. Reference to commercial products is made with the understanding that no discrimination is intended and no endorsement by the University of Minnesota any specific product(s) used in this implied.

6 Table 2. Foliar Applied Insecticide Control of Soybean Aphid 2016 performance of insectide compounds, rates, and timings for soybean aphid ontrol Lamberton, MN Bruce Potter and Travis Vollmer Applcation with C02 sprayer 15 GPA 40 PSI Rating Date 7/19 7/22 7/26 8/1 8/8 8/12 8/17 8/25 8/31 9/8 1/19-9/ Rating SB Aphid SB Aphid SB Aphid SB Aphid SB Aphid SB Aphid SB Aphid SB Aphid SB Aphid SB Aphid Cumulative YIELD Unit /plant /plant /plant /plant /plant /Plant /Plant /Plant /Plant /Plant aphid-days Bu. / Acre Days after First/Last Application 0 / 0 3 / 3 7 / 7 13 / / / 2 29 / 7 37 / / / 13% Appl. Appl. Ccrop Stage Date log* log* log* log* log* log* log* log* log* log* 1 Transform 0.75 oz/a R2 7/ a c 0.3 a c 3 a d 18 a cd 17.6 c c 55.7 c b 44.8 b b 61.2 c bc 6.95 d bc c b 69.1 b 2 Transform 0.75 oz/a R2 7/ a bc 0.2 a c 4.8 a cd 10.7 a d 23.8 bc c c b 75.7 b b 55.5 c cd 25 cd bc c b 72.0 a Priaxor 4.00 fl oz/a 3 Warrior II 1.60 fl oz/a R2 7/ a c 1.5 a bc 8.2 a cd a ab a a a a a a a a 62.9 bc a a a 66.3 c 4 Transform 0.75 oz/a R4 8/ a a 3.7 a a 18.3 a a 54.8 a abc 24.8 bc bc 22.4 c c 18.9 b de 8.9 c ef 2.7 d cd c bcd 68.5 bc 5 Transform 0.75 oz/a R4 8/ a bc 2.6 a abc 15.4 a ab 47.8 a abc 15.2 c c 5.75 c de 3.3 b e 3.7 c f 0.85 d d c cd 72.1 a Priaxor 4.00 fl oz/a 6 Priaxor 4.00 fl oz/a R4 8/ a bc 1.9 a abc 15.5 a ab 28 a bcd 66.1 bc ab bc b a a bc ab b a b a 69.5 ab 11 Warrior II 0.96 fl oz/a R4 8/ a ab 9.1 a a 12.7 a bc 65 a ab 11.8 c cde c c 74.1 b bc 82.7 c cde 3.55 d cd c b 69.0 bc 7 Warrior II 1.60 fl oz/a R4 8/ a bc 2.1 a abc 13.6 a ab 78.9 a ab 22.3 bc c c cd 29.5 b cd 51.4 c cd bcd b c b 69.9 ab 8 Endigo ZC 3.75 fl oz/a R4 8/ a bc 2.9 a ab 12.5 a bc 32.6 a a-d 10.3 c de 3.25 c e 8.8 b de 4.8 c f 2.35 d cd c d 69.1 b 9 Brigade 2.10 fl oz/a R4 8/ a bc 3.9 a abc 14.6 a abc 68.3 a ab 4 c e c c 11.7 b cde 29.3 c def 4.65 d cd c bcd 67.8 bc 10 Brigade 6.40 fl oz/a R4 8/ a bc 2.3 a abc 13.3 a bc 75.1 a a 26.2 bc cd c cd 23.9 b bc 36.6 c def 11 d bc c bc 69.8 ab 12 Untreated a abc 3.2 a abc 12.1 a bc 39.5 a abc 84.3 b a b a a a ab a a a ab a 67.4 bc LSD P= Standard Deviation Grand Mean Treatment F Treatment Prob(F) Means followed by same letter or symbol do not significantly differ (P=.05, LSD) Mean comparisons performed only when AOV Treatment P(F) is significant at mean comparison log* - To satisfy assumption of normality, mean seperations are based on log (10) transformed data

7 Figure 1. Effect of Selected Insecticides on Populations of Soybean Aphid - Lamberton, MN, 2016 * = insecticide application timing Warrior II 1.6 R2 Warrior II 0.96 Warrior II 1.6 Brigade 2.1 Brigade 6.4 Endigo ZC Transform 0.75 Untreated /19/16 R2 prophylactic 0.9 SBA/plant 8/10/16 R4 application (weather driven 92 SBA/plant w/ immigration Soybean aphids / plant * * 0 7/15 7/22 7/29 8/5 8/12 8/19 8/26 9/2 9/9 Sample date

8 Figure 2. Season-long Insecticide Effects on Soybean Aphid Populations (Cumulative Aphid-Days) and Soybean Yield Lamberton, MN, a Yield CAD 7/19/16 R2 prophylactic 0.9 SBA/plant 8/1016 R4 application (weather 92 SBA/plant and immigration a YIELD (Bushels/acre) +/- SEM Aphid - Days b b bc b bc c