ARS | Publication request: Droplet evaporation and spread on waxy and hairy leaves associated with type and concentration of adjuvants

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 18, 2011
Publication Date: June 15, 2011
Repository URL: http://hdl.handle.net/10113/49641
Citation: Xu, L., Zhu, H., Ozkan, E., Bagley, B., Krause, C.R. 2011. Droplet evaporation and spread on waxy and hairy leaves associated with type and concentration of adjuvants. Pest Management Science. 67:842-851. DOI: 10.1002/ps.2122.

Interpretive Summary: Pesticide spray application efficiency is often improved with the addition of adjuvants to spray mixtures. Enhanced droplet adhesion on leaf target surfaces usualy results. Use will be reduced resulting effective pest control if the active ingredients in droplets uniformly spread out and remain on the target area. This research determined the fate of water droplets amended with different classes of adjuvants at various concentrations on plant leaves. Variables included evaporation times, wetted areas and spread processes of the droplets after their deposition on waxy and hairy leaves of two different plant varieties using four representative types of adjuvants at five different concentrations. Test results clearly demonstrated the fact that the use of adjuvants could greatly improve the homogeneity of sprayed pesticides to increase the coverage area on target surface, thereby offering possibilities of reduced pesticide usage, and leading to economic benefit to the farmer and reduced risk of contamination of the environment by pesticides.

Technical Abstract: Adjuvants can improve pesticide application efficiency and effectiveness. However, knowledge is lacking on quantitative behaviors of adjuvant-amended pesticide droplets on foliage. Evaporation rates and wetted areas of 500 µm diameter water droplets amended with four adjuvants applied to waxy and hairy leaves were measured inside an environment-controlled chamber under the controlled conditions. The adjuvants included Crop Oil Concentrate (COC), Modified Seed Oil (MSO), Nonionic Surfactant (NIS), and Oil Surfactant Blend (OSB). Droplet evaporation rates and spread on either waxy or hairy leaves varied greatly with the adjuvants tested. On waxy leaves, the wetted areas of droplets containing COC were significantly smaller than those containing MSO, NIS or OSB whereas the evaporation rates were higher for COC amended droplets. On hairy leaves, COC amended droplets stayed on top of the hairy layer and did not penetrate this layer to reached the epidermis. When the relative concentration of the adjuvant was 1.50, the wetted area of droplets with NIS was 9.2 times lower than that with MSO and 6.1 times lower than that with OSB. The wetted area increased as the concentration increased. Droplets with MSO or OSB spread extensively on the hairy leaf surface until they dried completely. Results of this study demonstrated that addition of the proper concentration of MSO, NIS or OSB into spray mixtures improved homogeneity of spray coverage area on both waxy and hairy leaf surfaces, leading to strategies for reduction in pesticide use.