Bradley K. Fritz, Juan D. L ó pez, Jr., Daniel E. Martin, W. Clint Hoffmann, and Yubin Lan

1. Deposition on Corn Silks of Insecticides Aerially-Applied at High and Low Spray Rates for Control of Corn Earworm Bradley K. Fritz, Juan D. López, Jr., Daniel E. Martin, W. Clint Hoffmann, and Yubin Lan USDA-ARS Areawide Pest Management Research Unit College Station, TX ASABE/NAAA Technical Session, NAAA Convention , Las Vegas, NV, December 8, 2008

2. Organic Sweet Corn Protection • Premium for organically-grown sweet corn. • Problems with protection from pests because of limited availability of organic-approved pesticides for use. • Control of corn earworm, Helicoverpa zea, is a major concern. • Insecticide deposition on sweet corn ears, especially the silks is critical for corn earworm control.

4. Objectives • Quantify deposition on dryland field corn silks from aerial applications of Gemstar™ (1 application) and Entrust™(2 applications) at 5 gpa (VMDs at 230 and 400 μm) and 10 gpa (VMD at 400 μm). • Determine efficacy for control of corn earworm on ears of the different treatments for each insecticide application.

5. Use of Field Corn vs Sweet Corn • Sufficient acreages of sweet corn to conduct research not available in our area. • Cost of growing sweet corn in sufficient acreages to conduct research is high. • No major limitations on use of insecticides on nonBt field corn. • Producer nonBt field corn not generally treated with insecticides. • Hybrid seed corn production.

6. Methods and MaterialsInsecticides • Gemstar™ (Certis USA, L.L.LC., Columbia, MD); biopesticide; naturally-occuring virus of noctuid pests; approved for organic production; applied at 10 oz/acre in deionized water (pH 7) and Activator 90 (Loveland Products, Inc., Greeley, CO) at 16 oz/100 gal. with Caracid Brilliant Flavine fluorescent dye at 10 g/acre. • Entrust™(Dow AgroSciences LLC, Indianapolis, IN); spinosad; approved for organic production; applied at 1 oz/acre with above dye at 10 g/acre.

7. Methods and Materials Treatments for Each Insecticide Application

8. Methods and MaterialsApplication Equipment • Air Tractor 402B (Air Tractor Inc., Olney, TX) • CP-11TT nozzles (CP Products, Tempe, AZ) • 45 ft swath necessary to apply 10 gpa with setup • Settings obtained from USDA-ARS Spray Quality models (Kirk 2007)

9. Spray Treatment Setups, Droplet Sizes, and Operational Parameters Based on USDA-ARS Spray Quality models (Kirk, 2007)

10. Corn Earworm Study 2008 Field Layout for Field # 1 (6/3/2008) N REP 2 REP 3 REP 1 Parking Location Direction of Application Heading 313º Parking Location T2 R2 T3 R2 T3 R3 T4 R3 T2 R3 T1 R2 T4 R2 T1 R3 T2 R1 T3 R1 T4 R1 T1 R1 T1 –BLUE T2 – RED T3 – YELLOW T4 – WHITE REP 1 – Clint and Phil REP 2 – Juan, Roger, and Brad REP 3 – Dan and Yubin 1 2 3 4 5 Sampling Location Order Numbered as you are facing into the Field

11. Corn Earworm Study 2008 Field Layout for Field # 2 (6/6 & 9/2008) N REP 1 T4 R1 T1 R1 T2 R1 T3 R3 T3 R1 T2 R3 REP 3 Direction of Application Heading 314º and 135º T2 R2 T4 R2 T1 R2 T3 R2 T4 R3 T1 R3 T3 R1 REP 2 T1 –BLUE T2 – RED T3 – YELLOW T4 – WHITE 1 2 3 4 5 REP 1 – Clint, Tomi and Phil REP 2 – Juan, Roger and Brad REP 3 – Dan, Chris and Yubin Sampling Location Order Numbered as you are facing into the Field

12. Sampling layout of each treatment plot in each field location

13. Methods and MaterialsProcessing of Mylar and Silk Samples for Dye Deposition • Samples collected shortly after application. Nitrile gloves used. Mylar placed in labeled ziplock bags. Silk cut with scissors to drop into labeled ziplock bags from 2 ears, one from each adjacent row. Stored in cooler before analyses. • Each sample was washed with 30 ml ethanol in the ziplock bag and the wash assayed for fluorescense.

14. Methods and MaterialsPre and Post Corn Earworm Sampling • Presampling – in control plots only with 5 ears per mylar sampling location corresponding to sampling sites in treated plots. • Postsampling – in treated and control plots with 5 ears per sampling location. • Each ear checked for numbers of white or tan eggs on silks and small, medium, and large corn earworms in silk channel or ear tip.

15. Results and Discussion

16. Mean and standard deviation of meteorological conditions for three field locations during applications

17. Deposition Data and Separation of Means Means in the same column followed by the same letter are not significantly different based on Duncan’s Multiple Range Test (α = 0.05)

18. Test 1– Treatment Effects on Gemstar Efficacy for Corn Earworm Control • Presample (6/2/2008) – 0.008 white, 0.008 tan eggs/silk; 0.107 small larvae/silk. • Postsample (6/10/2008)- Control – 0.56 small and 0.48 large larvae/silk. T1 - 0.67 small and 0.53 large larvae/silk. T2 - 0.73 small and 0.47 large larvae/silk. T3 - 0.70 small and 0.35 large larvae/silk.

19. Conclusions • At 5 gpa, droplet size significantly affected deposition on mylar plates, but not on silks. • At 10 gpa and large droplets, there was significantly more deposition on mylar and silks than at 5 gpa. • No treatment effects detected for efficacy on control of corn earworms on ears. • Future research – more and timely applications; assess pattern of deposition on the silks due to treatment.