Impact of Precipitation on the Performance of Insecticides in Apples

1. Impact of Precipitation on the Performance of Insecticides in Apples John C. Wise, Ph.D. MSU Department of Entomology Trevor Nichols Research Center

2. Factors that Influence Pesticide Wash-off • Rainfall Characteristics • Penetrative & Translocative Properties of the Compound • Insecticide Inherent Toxicity and Application Rate • Drying time, Persistence, and Additives (image by Marlene Cameron)

3. Translocation and systemic mobility: Translaminar -penetration of a foliar applied pesticide from the adaxial cuticular surface of the leaf, through the epidermis layer and distributing into the mesophyll on the abaxial side. Acropetal - horizontal mobility in the plant xylem from central leaf tissue to the marginal ends. Basipetal - movement of the insecticide within the phloem from the site of application in the downward direction.

4. Insecticide Penetration in Fruits Penetration of the fruit cuticle follows the same process as described for leaves, but desorption into the epidermal cells of the hypanthium follows a simple diffusion process.

5. Physical and Chemical Properties

6. Objectives of Rainfastness Study • Determine the effect of rainfall on the performance of 7 different insecticides, representing the 6 chemical classes, against Codling moth (CM). • For each compound, determine the effect of rainfall and field-aging on CM toxicity, and • Measure the loss of foliar residues under .1, .5, 1 and 2 inches of simulated precipitation, compared to no-rainfall conditions. • Compare 2 hr to 24 hr drying time • Compare different adjuvants

7. Methods Rainfall Simulation Field Spray Bioassays Residue Analysis

8. Insecticides tested

9. Fruit Residues Results – Phosmet CM Bioassay • No significant effect of rainfall • Significant effect of aging Leaf Residues Proportion alive (two-way ANOVA on arcsine square-root transformed data, (P=0.05, Tukey’s HSD))

10. Fruit Residues Results – Thiacloprid CM Bioassay • Significant effect of rainfall • No significant effect of aging Leaf Residues Proportion alive (two-way ANOVA on arcsine square-root transformed data, (P=0.05, Tukey’s HSD))

11. Fruit Residues Results – Acetamiprid CM Bioassay • No significant effect of rainfall • No significant effect of aging Leaf Residues Proportion alive (two-way ANOVA on arcsine square-root transformed data, (P=0.05, Tukey’s HSD))

12. Fruit Residues Results – Novaluron CM Bioassay • Significant effect of rainfall • No significant effect of aging Leaf Residues Proportion alive (two-way ANOVA on arcsine square-root transformed data, (P=0.05, Tukey’s HSD))

13. Fruit Residues Results – Spinetoram CM Bioassay • Significant effect of rainfall • No significant effect of aging Leaf Residues Proportion alive (two-way ANOVA on arcsine square-root transformed data, (P=0.05, Tukey’s HSD))

14. Fruit Residues Results – Rynaxypyr CM Bioassay • Significant effect of rainfall • No significant effect of aging Leaf Residues Proportion alive (two-way ANOVA on arcsine square-root transformed data, (P=0.05, Tukey’s HSD))

15. Residue Wash-off Profiles for Asana

16. Rainfastness Rating ChartGeneral Characteristics for Insecticide Chemical Classes • H – highly rainfast (≤30% loss), M – moderate (≤50% loss), L – low (≤70% loss), S-systemic residues • Michigan Fruit Management Guide E154 http://bookstore.msue.msu.edu/

17. Apple Insecticide Precipitation Wash-offRe-application Decision Chart:Expected codling moth control in apples, based on each compound’s inherent toxicity to CM larvae, maximum residual, and wash-off potential from rainfall. * Number of days after insecticide application that the precipitation event occurred. X – Insufficient insecticide residue remains, thus re-application is recommended.

18. (2 h drying) (24 h drying) Residue Wash-off Profiles for Imidan

19. Residue Wash-off Profiles for Calypso (2 h drying) (24 h drying)

20. Residue Wash-off Profiles for Assail (2 h drying) (24 h drying)

21. Impact of Adjuvants on Imidan Rainfastness

22. Impact of Adjuvants on Assail Rainfastness

23. Implications for Insecticide Performance • All compounds maintained good activity with up to 0.5 inch simulated rainfall (24 h drying), showing little need to immediately re-apply. Short-lived materials may require re-application when 0.5 in of rain occurs after 7 days of field aging. • Organophosphate insecticides appear to be most susceptible to wash-off, but high toxicity to the pest may compensate for residue loss. • Carbamate and pyrethroid insecticides are moderately susceptible to wash-off, and are generally short-lived, but in some cases inherent toxicity compensates for loss. • Neonicotinoid surface residues are susceptible to wash-off, but sub-surface residues remain stable. Longer drying periods before rainfall will allow maximum plant penetration and improve rainfastness. • IGR compound rainfastness is moderate to high up to 1 in rain. • The performance of Spinosyn and Diamide compounds appear to be the least affected by precipitation, with rainfastness ranging from moderate to high up to 1 inch of rainfall. • Adjuvants can improve pesticide deposition and rainfastness.

24. The TNRC staff say thank you to the Michigan Apple Research Committee for making this research possible