Submitted to: National Agricultural Aviation Association Meeting
Publication Type: Proceedings
Publication Acceptance Date: December 8, 2008
Publication Date: December 8, 2008
Citation: Fritz, B.K., Lopez, J., Latheef, M.A., Martin, D.E., Hoffmann, W.C., Lan, Y. 2008. Deposition of insecticides on corn silks applied at high and low spray rates for control of corn earworm. National Agricultural Aviation Association Meeting. Paper No. AA08-004. Interpretive Summary: Damage to sweet corn resulting from corn earworm is a major concern to growers potentially resulting in severe economic impacts. Control is typically obtained through aerial application, though limited guidance is available for applying optimum treatments. A series of field studies were conducted examining various spray rates and droplet sizes for maximum deposition of active ingredient onto the corn ear silks. Generally, higher spray rates with larger droplet sprays increased the amount of material deposited on the corn ear silks. The results provide applicators with information on optimum treatments to control corn earworm and reduce crop damage.
Technical Abstract: Corn earworm is a major pest of sweet corn, especially when grown organically. Aerial application of insecticides is important for both conventionally- and organically-grown sweet corn production as sweet corn is frequently irrigated to assure return on investment given the high production costs. Aerial insecticide application costs can be minimized through use of reduced spray rates if insecticide efficacy can be maintained at the lower spray rates. The objectives of the study were to characterize deposition on field corn silks when applied at 5 gpa (with VMDs at 230 and 400 µm) and 10 gpa (with VMD at 400 µm) spray rates. Applications of the bioinsecticide, Gemstar®, and the insecticide, Entrust®, which are both approved for use in organic production, were made over three different fields. The amount of spray material deposited on individual silks for each treatment was determined. Deposition of spray material on the silks was very similar across all application treatments. Overall, the 10 gpa rate resulted in the greatest deposition of active material on the corn silks. At the 5 gpa rate, the smaller droplet size sprays resulted in less deposition than the other treatments. Efficacy determinations were attempted by counting the number of larvae of different sizes per ear before and after treatment applications. Heavy reinfestations of ear worms negated much of the efficacy work, but did point out the potential need for timely follow-up treatments.