Insecticide evaluations for soybean aphid management: the good, the bad and their residual times Kevin D. Johnson and Matt O’Neal Soybean Entomology Lab Department of Entomology I want to thank everyone for coming out this morning. My name is Kevin Johnson and I’m a Ph.D. candidate in the soybean entomology lab hear at Iowa State under Dr Matt O’Neal. Over the last few years my research has revolved around soybean aphid management, and I’m going to share some of my research with you today.

Soybean aphid impact Damage ~25% yield reduction documented in Iowa Phloem “sap” feeding Sooty mold Virus vectoring ~25% yield reduction documented in Iowa Possible economic loss of $163 per acre* The soybean aphid has dramatically changed soybean production in discovery in 2000. * Assuming 65 bu per acre and $10 per bu

Soybean aphid populations Mean aphids per plant + SEM This figure shows SBA populations in at one of our story county sites Year to year variability Story County

Insecticide use in Iowa soybeans 2003 ~ 4 million acres 2004 ~100-250,000 acres 2005 ~2 million acres 2006 ~100-250,000 acres 2007 ~4-5 million acres The year to year variability can be seen in annual insecticide usage trends Photo Purdue Univ.

Questions about soybean aphid management in Iowa What products provide the greatest yield protection? What products provide the greatest protection over time? How important is coverage? Is the economic threshold static or dynamic? How do current recommendations hold up in the field?

Cumulative aphid days A good way to visualize treatment differences Analogous to degree days Estimate plant exposure to aphids Examples 10 aphids for 10 days = 100 CAD 100 aphids for 10 days = 1000 CAD 1,000 aphids for 10 days = 10,000 CAD Befor I start answering these management questions I want to take a second or two and talk about CAD’s Top fig is aphids per plant Bottem fig shows the exact same data as cumulative aphid days.

Insecticide efficacy

Questions involving insecticides for soybean aphid management What insecticides protect soybean yield from aphids? What insecticides last for the longest period of time following application?

Materials and Methods 32 Treatments in a Randomized Complete Block Design 6 replications in 2007 1 Location We have been conducting these efficacy trials for the last 4 years however I’m only going to share the 2007 data from the northeast research farm. These were all small plot trials. The image to the right is of me applying one of these treatments. Fun in the sun!!

Statistical analysis Aphid population data required log transformation Yield data did not require transformation Analyzed using an one-way analysis of variance (ANOVA) Treatment differences were determined significant at P < 0.05 All of the analysis for the experiments I’m going to showing you today will be identical to this. So I’ll only show it to you once.

Aphid arrival and peak populations Control Treatment Aphid Peak Location Arrival Population Date Floyd 11 June 915 13 Aug In 2007 at floyd county Plots were planted on 15 May

Commercially available products Treatment Rate Active Ingredient Target Application control --------- ----------- zero aphid 3.2 oz + 4 oz λ-cyhalothrin + chlorpyrifos Cruiser 100 g thiamethoxam ST 50 g Cruiser + Warrior 50 g + 3.2 oz thiamethoxam + λ-cyhalothrin ST + 250 Warrior 3.2 oz λ-cyhalothrin 250 Gaucho 62.5 g imidacloprid Gaucho + Baythroid 62.5 g+ 2.4 oz imidacloprid + cyfluthrin Baythroid 2.4 oz cyfluthrin Cobalt 13 oz γ-cyhalothrin + chlorpyrifos Lorsban 4E 16 oz chlorpyrifos NuFos 8 oz clorpyrifos Dimethoate dimethoate Penncp-M 2 pt parathion 250  I’d like to draw your attention to Cobalt…. Also the foliar products are all contact insecticides. The aphid free control was treated with insecticides four times (15 June, 6, 22 July, and 13 August). Aphid populations averaged 240 aphids per plant 3 days prior to the application of the foliar insecticides. Treatments were applied 28 July

Available foliar products Mean cumulative aphid days (+SEM) 12000 66 a Mean yield bu per acre (+SEM) B ab ab ab ab ab 64 10000 ab ab ab 62 8000 b 60 6000 58 4000 A 56 c 2000 Cumulative aphid days are represented by bars and capital letters. Yields are represented by triangles and lowercase letters. Means with a unique letter are significantly different (P < 0.05). A A 54 A A A A A A A 52 Untreated control Cruiser + Warrior Gaucho + Baythroid Baythroid Dimethoate Penncap-m Aphid Free Warrior Cobalt Lorsban NuFos

Available seed treatments Mean cumulative aphid days (+SEM) 12000 66 A a Aphid free Mean yield bu per acre (+SEM) D A a Warrior a a 64 10000 62 b b 8000 C 60 6000 58 C 56 4000 c c 54 2000 B A I’m going to switch the Zero aphid treatment with an single application of a pyrethroid. I want to illustrate how these products held up to a single application of a foliar pyrethroid Cumulative aphid days are represented by bars and capital letters. Yields are represented by triangles and lowercase letters. Means with a unique letter are significantly different (P < 0.05). 52 A 50 Untreated control Cruiser 100g (2X) Cruiser 50g Cruiser + Warrior Gaucho Gaucho + Baythroid

Residual time of labeled treatments 100 10 20 30 40 50 60 70 80 90 7/30 8/7 8/13 8/17 100 200 300 400 500 600 700 800 900 1000 7/30 8/7 8/13 8/17 Untreated Control Mean aphids per plant Aphid Free Cruiser 100 Warrior Baythroid Cobalt Lorsban NuFos Solid lines represent pyrethroids (PY) and dashed lines represent organophosphates (OP). Cobalt is a pre-packaged mix PY + OP. When averaged OP’s have a slope of positive 1 and PY’s have a slope of negative 1. Dimethoate Penncap-m

Experimental Treatments Rate Active Ingredient Target application control --------- ----------- zero aphid 3.2 oz + 4 oz λ-cyhalothrin + chlorpyrifos Trimax + NIS 1.35 oz imidacloprid 250 Trimax + COC + UAN Trimax + Baythroid + COC 1.35 oz + 2.4 oz imidacloprid + cyfluthrin spirotetramat + COC 4 oz spirotetramat 6 oz Trimax + spirotetramat + COC 1.35 oz + 4 oz imidacloprid + spirotetramat 1.35 oz + 6 oz 400 potassium silicate 0.5% v/v 1% v/v I’d like to point out that these are mostly plant systemic insecticides. This is a point that I’ll bring up later in the talk. Surfactants The aphid free control was treated with insecticides four times (15 June, 6, 22 July, and 13 August). Aphid populations averaged 240 aphids per plant 3 days prior to the application of the foliar insecticides.

Experimental treatments Mean cumulative aphid days (+SEM) a 14000 a 66 Mean yield bu per acre (+SEM) ab ab ab ab ab C 12000 C b C 61 10000 b b 8000 56 c B B 6000 c c 4000 51 Cumulative aphid days are represented by bars and capital letters. Yields are represented by triangles and lowercase letters. Means with a unique letter are significantly different (P < 0.05). 2000 A A A A A A A A 46 Spirotetramat 4 oz Spirotetramat 4 oz + Trimax Spirotetramat 6 oz Spirotetramat 4 oz (400) Spirotetramat 6 oz (400) Spirotetramat 6 oz + Trimax Potassium silicate 0.5% Potassium silicate 1.0% Trimax + COC Trimax + NIS Trimax + Baythroid Untreated control Aphid Free

Conclusions Timing is more important that product selection Multiple insecticide applications did not protect yield beyond a single insecticide application. Insecticides applied at 250 aphids per plant provide consistent yield protection. Seed treatments did not prevent economic injury level. Seed treatments lack residual activity to control aphids. FOR SBA’s. Caveat spider mites?

Insecticide Coverage Now that I’ve talked about the chemicals I want to talk about how to apply them.

Insecticide coverage objective Determine if application technique influences aphid control when using: Pyrethroids Organophosphates Tank-mixes (Pyrethroids and Organophosphates)

Droplet size Fine Coarse Same volume American Society of agricultural engineers has developed a ranking system which breaks droplet sizes into 5 categories xc c m f vf

= Droplet size and coverage 250 Microns 250 Microns 500 Microns 250 Reducing to droplet size by 1/2 results in 8 times more droplets Smaller droplets almost double the surface area Volume of a sphere 4πr2 250 Microns 250 Microns 250 Microns

Experimental Treatments Approximately 400 microns to 200 microns in size 8 times the number of droplets from 1/2 the size and double that due to change in volume = 16 times the number of droplets results in almost 400% increase in surface area TeeJet 11002 Twin Jet TeeJet 8001 Extended Range

Materials and Methods 9 Treatments in a Randomized Complete Block Design 6 replications 3 Years 2 Locations Small plot

Peak aphid populations Control Treatment Peak County and Year Population Date Floyd 2007 563 18 August Story 2007 1121 14 August Floyd 2006 171 11 August Floyd 2005 413 31 August

Experimental treatments Mean yield (+SEM) 65 A 64 AB A 63 AB A 62 AB AB B 61 60 59 C 58 57 56 I going to skip the CAD’s and go strait to the money with this data. Because this is an average of 3 years and 2 locations it is difficult to say exactly when beans were planted and when insecticides were applied. As a rule we targeted 250 aphids per plant or the first week of aug, and 3 to 5 applications of insecticide in the aphid free control 55 Untreated Aphid Free (Very fine) Medium Fine Very fine Medium Very fine Medium Very fine Controls Pyrethroids Organophos. Tank-mix

Effect of chemistry Mean yield (+SEM) 65 64 63 62 61 60 59 58 57 56 55 Pyrethroids Organophosphate Tank-mix

Effect of coverage Mean yield (+SEM) Medium Very fine 65 64 63 A 62 61 B 60 59 58 1.6 bu 57 56 55 Medium Very fine

Conclusions Improved coverage = Improved control Improved control = Improved yield 1.6 bu per acre Coverage is more important that product What about systemic products? How will my recommendations change when systemic insecticides are available?

Economic thresholds

Dynamic Thresholds Economic injury level is the point where the cost of control = the damage caused by the pest Economic injury levels are not static! EIL = * 100 C = Cost of control (pesticide + application) V = Market value Y = Yield

Dynamic Thresholds EIL = * 100 EIL ET Time Aphid per plant EIL ET What happens when the Value of crop increases? Time

Economic Threshold for Soybean Aphid. Points to consider The current economic threshold is dynamic not a static 250 aphids per plant. However …… D. W. Ragsdale, B. P. McCornack, R. C. Venette, B. D. Potter, I. V. MacRae,E. W. Hodgson, M. E. O’Neal, K. D. Johnson, R. J. O’Neil, C. D. Difonzo, T. E. Hunt, P. Glogoza, and E. M. Cullen 2007. Economic Threshold for Soybean Aphid. Journal of Economic Entomology 100(4) 1258-1267 Other thresholds are considered in the paper Residual activity Reentry intervals Multiple insecticide applications

Labeled foliar treatments Mean cumulative aphid days (+SEM) 12000 66 a Mean yield bu per acre (+SEM) B ab ab ab ab ab 64 10000 ab ab ab 62 8000 b 60 6000 58 4000 A 56 c 2000 A A 54 A A A A A A A 52 Untreated control Cruiser + Warrior Gaucho + Baythroid Baythroid Dimethoate Penncap-m Aphid Free Warrior Cobalt Lorsban NuFos

In the Field As part of an USDA Regional Area Management Plan Scout 250 Single application

Testing recommendations in the field. 4 Treatments in a Randomized Complete Block Design 6 replications 3 Years 2 Locations each year Large plot 1 to 1/2 acre.

Treatments Treatment Insecticide Time of Application Control Preventative Warrior + Headline R1-R2 IPM approach Warrior 250 aphids per plant Seed treatment Cruiser seed treatment

Peak aphid populations Control Treatment Peak Year County Population Date 2007 Story 2765 18 August Lucas 356 6 August 2006 Story 6 8 August Lucas 21 9 August 2005 Story 290 6 September Lucas 60 8 September Soybeans were starting to synes in 2005 and populations crashed in 2007 at Lucas county in 2007. This resulted in only story county receiving all insecticides.

Story County 2007 Mean cumulative aphid days (+SEM) A 60000 50000 40000 B B 30000 B B 20000 B Prevent and IPM were applied at the same time 7 July. 10 aug for seed trt 20 aug for IPM and prevent 10000 Untreated Preventative Preventative + IPM IPM + 250 Seed trt + 250 250

Mean yield bu per acre (+SEM) Story County 2007 70 Mean yield bu per acre (+SEM) A A A A A 60 50 B Prevent and IPM were applied at the same time 7 July. 10 aug for seed trt 20 aug for IPM and prevent 40 30 Untreated Preventative Preventative + 250 IPM IPM + 250 Seed trt + 250

Conclusions Scout the field!!!!! Multiple insecticide applications did not protect yield. Preventative treatments did not maintain aphid populations below the threshold. Preventative treatments did not protect yield. Medium

Acknowledgements USDA Funding from Iowa Soybean Association Industry Partners Bayer CropScience BASF Cheminova Dow AgroSciences FMC NuFarm PQ Syngenta Valent Graduate students Nick Schmidt Wayne Ohnesorg

Questions?

Dynamic Thresholds EIL = * 100 EIL ET Time Aphid per plant EIL ($ equipment, $chemicals) ET What happens when the Value of crop increases? What happens if my applicator breaks down and I have to pay a custom applicator to do apply at a higher cost? We purchas a new applicator and the time it takes to apply the insecticide decreases? Time