Seed applied insecticide efficacy against the Soybean Aphid (Aphis glycines) and Bean leaf beetle (Cerotoma trifurcata)

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1 Seed applied insecticide efficacy against the Soybean Aphid (Aphis glycines) and Bean leaf beetle (Cerotoma trifurcata) Bruce Potter, University of Minnesota Department of Entomology and Southwest Research and Outreach Center Summary During 2004, Gaucho and several formulations of Cruiser applied to seed, and foliar applications of Warrior were compared on two planting dates at the University of Minnesota Southwest Research and Outreach Center, Lamberton, MN. Treatments consisted of insecticide untreated, cruiser applied to seed at 50 grams/100kg seed, with and without a foliar application of warrior at 3.2 fl. oz/acre targeted against soybean aphid, Cruiser at mg/seed, and as a prepak formulation with Apron+Maxim, gaucho at 62.5 grams/100 kg seed, Warrior at 3.2 fl. oz./acre applied early (VC), at soybean aphid treatment threshold (peak soybean aphid population), and as needed to maintain a bean leaf beetle and soybean free treatment through the growing season. Under low 2004 soybean aphid and bean leaf beetle populations no difference in soybean growth or yield were observed among treatments. Both planting dates yielded similarly. The yield of insecticide untreated plots was somewhat less than those receiving a seed or foliar insecticide applications in the late planting date. However, the low yields were limited to of the two untreated plots. These yield differences were not statistically significant and did not appear to be related to insect infestations or the components of soybean yield that were measured. Background The soybean aphid (SBA) is a relatively new pest of Minnesota soybeans. It was first identified during the late summer of 2000 in SE MN. SBA subsequently spread throughout the soybean growing areas of MN during the 2001 growing season with localized yield limiting populations in During 2003, widespread economic infestations and treatment of soybean aphid occurred. Bean leaf beetle and bean pod mottle virus transmitted by the beetle have been a problem in Southwest Minnesota over the past few years. Bean leaf populations were also lower in 2004 than previous years. Management of both insects is problematic. Soybean aphids are unpredictable in timing and location of occurrence. Additionally, the potential for extremely rapid population increase makes timely treatment difficult. In the case of bean leaf beetle, multiple and overlapping generations make timing of scouting and insecticide applications difficult. There are timing issues with foliar treatments. Insecticide applied too early can lead to egg lay by late arriving bean leaf beetles while insecticide applied too late may allow egg lay before beetles are killed. Previous studies in SW Minnesota suggest that seed applied insecticides might be effective in

2 preventing early season bean leaf beetle injury and associated virus transmission and could reduce early to mid season soybean aphid populations. Substantial data supporting an aphid treatment threshold of 250 aphids /plant was obtained in studies during 2003 including a study similar to this trial. Objective This trial was designed to examine: 1) soybean aphid control with seed applied insecticide compounds and formulations compared to foliar applied insecticides 2) the effect of seed applied insecticides on over-wintering bean leaf beetle populations and 3) the comparative performance of these products at two planting dates. Site description and application description The trial was planted at the University of Minnesota, Southwest Research and Outreach Center near Lamberton, Redwood County, Minnesota. Site and application details are shown below. Several farm woodlots and the adjacent Cottonwood River area contain buckthorn, Rhamnus sp, the winter host for soybean aphids. The 2004 growing season was well below average (261 GDD below average May 1 - September 30) in temperature and above average in rainfall (8.22 inches above average May 1 - September 30). The cool season resulted in less vegetative soybean growth than typical. However, a very warm September produced good yields in this trial due to good fill of the pods produced and large seed size. Detailed temperature and rainfall information for this location can be found at The soybean aphid infestation was detected late and very slow to develop during Aphids were first detected at this location on July 14 when very small colonies tended by ants near a woodlot were observed although aphids were probably present at very low, undetectable levels earlier. Although individual plants in this trial had high aphid populations, many plants in untreated checks were never colonized and infestations remained low throughout the season. Bean leaf beetle populations were low as well. County: Redwood, MN Nearest town: Lamberton, MN Soil type: Normania and Ves loams, Webster clay loam Fertility: P(bray)- 17 ppm, K 144 ppm, ph 5.9 Previous crop: Corn Tillage: Soil save Fall 2002 Field cultivator 2x 4/30/04 Cultivar: NK X417R (roundup ready cyst nematode resistant) Planting date: Early - May 3, 2004 early, Late - May 27,2004 Seeding rate: 175,000 seeds/acre Row spacing: 30

3 Weed control: 2.5 pt./acre PPI 4/30/04 PPI Roundup 22 oz./acre 7/22/04 POST Design: Randomized complete block with 4 replications Plot size: 10 x 50 Foliar insecticide application date(s) early application: Date: 1) Early 6/8/04 late 6/15/04 2) 7/23/04 3) 8/14/04 Wind: 3-5mph 5mph 0-5mph Calm Temp: 61F 65F F 65 F Crop stage: VC VC V8/R2 V12-V10 R4 Syngenta Crop Protection, Stanton, MN, applied insecticide and fungicide to seed. All treatments had ApronMaxx (mefanoxam+ fludioxonil) fungicide applied to seed at the rate of 6.25 grams/100 kg seed. Foliar insecticide treatments were applied with a CO2 backpack sprayer (R&D Sprayers) with 8002XR flat fan nozzles on 18-inch spacing, 20 gallons/acre and 30 PSI. Planned treatments consisted of Cruiser (thiomethoxam) applied at 50 g/100kg seed, with and without a foliar application of warrior (l-cyhalothrin) targeted against soybean aphid, at mg/seed, and as a prepak formulation with apron maxim, Gaucho (imidichloprid) at 62.5 grams/100 kg seed, Warrior applied early (VC), at soybean aphid treatment threshold, and as needed to maintain a bean leaf beetle and soybean free treatment through the growing season. This trial was planted at two dates and early date (May 03, 2004) to provide early emerging soybeans attractive to overwintering bean leaf beetle adults. An additional late planting (May 27, 2004) date to provide soybeans suitable for soybean aphid late inthe season. However, both insects occurred in both planting dates of this trial and their populations were noted. Soybean plant populations and Bean leaf beetle populations and injury were based on five 1-meter sections of row/plot. Soybean aphid populations, soybean stage and growth were obtained by sampling 5 representative plants/plot/ date. Results and discussion Populations of both bean leaf beetle and soybean aphid were low in Cold, dry soil conditions, delayed emergence of the early planting date and the early and late planting dates emerged approximately within 1 week of each other. In addition to the low overall bean leaf beetle populations at this location, the late emergence of the early planting further limited infestations of this insect. Soybean yield, bean leaf beetle and soybean aphid populations are shown in tables 1 and 2 for the early and late planning dates respectively. Plant injury was not observed with any of the treatments. No differences in soybean plant population or growth were observed. Higher plant populations and

4 increased growth were observed in similar trials in 2002 and increased growth observed in 2003, with seed corn maggot being present in 2002 and higher bean leaf beetle and soybean aphid populations in both years. Plants with virus symptoms were occasionally observed but incidence were much too low to quantify. Analysis of the levels of percent bean pod mottle virus symptomatic seed is pending. Fungal root rots were observed in all treatments early and mid-season but root systems had recovered by late season. In the early planting date, although populations were low, bean leaf beetle damage as percentage of plants was significantly lower in all treatments with seed applied Cruiser or Gaucho and some damage had occurred by the time of the early foliar application of warrior. Bean leaf beetle populations were too low to be accurately rated in the late planting date with beetles observed in only two of the plots. Soybean aphid populations were very low through the season with slightly higher populations occurring in the late planting date. As typical, under low aphid infestations, great variability in plant-to-plant populations occurred and this is reflected in high c.v. values. Treatments targeted to a 250-soybean aphid/plant threshold were applied at much lower levels, < 15 aphids/plant (most of this average coming from one plant) and < 5 aphids/plant threshold in early and late planting dates respectively. The 116 aphid/plant estimate in the Cruiser treatment on 8/12/04 is also the result of a single heavily colonized plant. The effectiveness of foliar insecticide applications might be inferred at both planting dates. No differences in soybean yield were detected between treatments in the early planting date or late planting date. In the late planting date, two of the four insecticide free check plots located the south end of the trial yielded less than other plots. This required transformation of the yield data to allow an analysis of variance. The yield results given in table 2 are reported in untransformed units. A 25- foot roadway separated these plots from bulk planted soybeans to the south. There does not appear to be a reason for these low yields from the appearance of the study during the growing season or the insect and growth data collected and it seems unlikely that insect control at varied application timings could had provided equivalent insect feeding or disease vector control. These data suggest provide additional information that seed applied insecticide treatments (if labeled) can provide control of overwintering bean leaf beetle.. Previously observed growth differences for seed applied insecticides might be inferred to be insect related. Unfortunately, the low, difficult to quantify insect populations in this trial prevent confidence in evaluating relative insecticide performance between treatments. These 2004 data reinforce the value of

5 economic thresholds and scouting as well as other tenets of Integrated Pest Management. Although they are easy to include in a crop management program, prophylactic treatments for plant pests have a down side potential in that economic return will be negative under low pest populations. Acknowledgments: Many thanks to Derek Erickson, Mellisa Olsem, and Mark Anderson for aphid counting. Yield data would not have been possible without the intrepid SWROC mobile plot crew of Steve Quiring and Jeff Irlbeck. Gaucho Register trademark of Bayer Crop Science and is not currently labeled on Soybean in MN Cruiser Registered trademark of Syngenta Crop Protection, Inc. and not currently labeled on soybean in MN Warrior and Registered trademark of Syngenta Crop Protection, Inc. ApronMaXX, Trademark of Syngenta Crop Protection, Inc. 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 1. The effect of seed applied insecticide on bean leaf beetle, soybean aphid and soybean growth - May 5 th planting date. University of Minnesota Southwest Research and Outreach Center, Lamberton, MN. (2004). B. Potter Rated plants BLB % plants w/ BLB feeding SBA Soybean Nodes branch nodes pods %pods w/ /meter row /meter row BLB feeding sites/plant /plant height (CM) /plant /plant /plant BLB feeding 13% moisture Date 06/07/04 06/07/04 06/07/04 06/07/04 08/18/04 10/01/04 10/01/04 10/01/04 10/01/04 10/01/04 10/04/04 4 DAT Soybean stage V1 V1 V1 V1 V13/R5 V14/R8 V14/R8 V14/R8 V14/R8 V14/R8 R8 APRON MAXX RFC 6.25 g AI/100KG a 0.05 a a 0.65 a 2.5 a a 15.7 a 5.1 a a 0.46 a 49 a insecticide untreated APRON MAXX RFC 6.25 g AI/100KG a 0 a 0.87 b 0.02 a 0.9 a 79.8 a 15.6 a 4.6 a 29.4 a 0.5 a 50.5 a APRON MAXX RFC 6.25 g AI/100KG 24.3 a 0 a 1.18 b 0.04 a 0 a a a 7.95 a 35.4 a 0 a 50 a Warrior 3.2 fl oz/a targeted against SBA 8/14/04 APRON MAXX RFC 6.25 g AI/100KG 24.1 a 0 a 0 b 0 a 1.5 a 79.2 a 16 a 5.4 a a 0.12 a 49.6 a Cruiser mg/seed APRON MAXX RFC 6.25 g AI/100KG 26.1 a 0 a 0.42 b 0 a 0.4 a a 15.9 a 5.9 a 32.3 a 0.26 a 49.7 a Gaucho 62.5 G AI/100kg A14379A prepak a 0 a 0.16 b 0 a 2.8 a a a 4.9 a a 0 a 50.3 a APRON MAXX RFC 6.25 g AI/100KG a 0.15 a ab 0.37 a 0.5 a a a 5.15 a a 0.16 a 49.8 a Warrior 3.2 fl oz/acre early 6/08/04 V1 APRON MAXX RFC 6.25 g AI/100KG a 0 a ab 0.57 a 0 a a a 5.9 a a 0.13 a 50 a Warrior 3.2 fl oz/acre 8/14/04 R5 APRON MAXX RFC 6.25 g AI/100KG 24 a 0.05 a a 0.92 a 0 a 80.2 a a 6.4 a 31.8 a 0.13 a 50.6 a 3.2 fl. oz./acre Insect free 3 applications 6/8/2004, 7/23/04, 8/14/04 LSD (P=.05) N.S. N.S N..S. N.S. N.S. N.S. N.S. N.S. N.S. N.S. Standard Deviation CV Grand Mean P(Bartlett's X2) * 0.001* 0.001* * Prob (F) Means followed by same letter do not significantly differ (P=.05, Duncan's New MRT) t=mean descriptions are reported in transformed data units, and are not de-transformed. Mean comparisons performed only when AOV Treatment P(F) is significant at mean comparison OSL.

7 Table 2. The effect of seed applied insecticide on bean leaf beetle, soybean aphid and soybean growth - May 27 th planting date. University of Minnesota Southwest Research and Outreach Center, Lamberton, MN. (2004). B. Potter Rated plants % plants w/ SBA SBA Soybean nodes branch nodes pods meter row BLB feeding /plant /plant height (CM) /plant /plant /plant 13% moisture Date 6/14/04 6/14/04 8/12/04 8/20/04 10/06/04 10/06/04 10/06/04 10/06/04 10/07/04 6 DAT Crop Stage VE-VC VE-VC V12-13/R4 V13/R5 V13-14/R8 V13-14/R8 V13-14/R8 V13-14/R8 R8 APRON MAXX RFC 6.25 g AI/100KG 26.8 a 0.7 a 4.2 a 9.4 a 80.1 a 15.1 a 2 a 27.1 a 45.4 a insecticide untreated APRON MAXX RFC 6.25 g AI/100KG 26.6 a 0.2 a a 10.3 a 79.8 a 15.7 a 2.6 a 26.9 a 49.3 a APRON MAXX RFC 6.25 g AI/100KG 26 a 0 a 1.0 a 0 a 79.7 a 15.5 a 1.9 a 26.9 a 50.4 a Warrior 3.2 fl oz/a targeted against SBA 8/14/2004 APRON MAXX RFC 6.25 g AI/100KG 25.7 a 0 a 0.3 a 2.3 a 81 a 15 a 2.3 a 26.1 a 48.7 a Cruiser mg/seed APRON MAXX RFC 6.25 g AI/100KG 25.7 a 0 a 0.3 a 3 a 81.6 a 16.1 a 1.5 a 30.1 a 49.2 a Gaucho 62.5 G AI/100kg A14379A prepak 26.4 a 0 a 0.2 a 1.6 a 80 a 16 a 2.8 a 29.7 a 47.8 a APRON MAXX RFC 6.25 g AI/100KG 24.8 a 0 a 24.9 a 7.4 a 78.5 a 16 a 3 a 33.8 a 50 a Warrior 3.2 fl oz/acre early 6/15/2004 APRON MAXX RFC 6.25 g AI/100KG 26.6 a 0 a 2.8 a 0 a 79.3 a 15.4 a 3.3 a 30.8 a 50.5 a Warrior 3.2 fl oz/acre 8/14/2004 APRON MAXX RFC 6.25 g AI/100KG 23.5 a 0 a 0.1 a 0 a 80.2 a 15.9 a 2.8 a 29.4 a 50.2 a 3.2 fl. oz./acre insect free applicatons 6/15/04, 7/23/04,8/14/04 LSD (P=.05) N.S. N.S N.S. N.S. N.S. N.S. N.S. N.S. N.S. * Standard Deviation CV Grand Mean P(Bartlett's X2) * 0.001* * * Prob (F) Means followed by same letter do not significantly differ (P=.05, Duncan's New MRT) Mean comparisons performed only when AOV Treatment P(F) is significant at mean comparison OSL.