Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2014
Publication Date: 3/1/2015
Publication URL: http://handle.nal.usda.gov/10113/61352
Citation: Derksen, R.C., Canas, L.A., Ranger, C.M., Reding, M.E. 2015. The effect of application method on the temporal and spatial distribution of neonicotinoid insecticides in greenhouse zinnia and impact on aphid populations. Applied Engineering in Agriculture. 31:211-216.
Interpretive Summary: While good sanitation practices and other Integrated Pest Management techniques are used by growers to prevent infestation, sometimes outbreaks do occur and it is necessary to use insecticides. The use of neonicotinoid insecticides has helped improve the management of various insects that attack floriculture crops in greenhouses. Neonicotinoids have broad spectrum activity that interferes with an insect’s nervous system. Greenhouse trials were initiated to evaluate how far the neonicotinoids imidacloprid and thiamethoxam moved in potted zinnia 10 days after treatment with either a drench application or foliar application to a single, mid-stem leaf. Adult aphids were caged to the underside of leave study the efficacy provided by the insecticides as they moved through the plant system. Imidacloprid and thiamethoxam are both good tools for the management of aphids as confirmed by the low numbers of live aphids found on leaves with high levels of the insecticides. The method of delivering the insecticides can significant affect the biological efficacy. The drench treatments in this study were far superior to the spray treatment resulting in leaves with higher levels of imidacloprid and thiamethoxam. The spray treatment accumulated lower levels of insecticides and resulted in less aphid mortality compared to the drench treatment. These results demonstrate the need to ensure good spray distribution during foliar application of insecticides, even if these insecticides have known systemic activity.
Technical Abstract: Greenhouse trials were designed to evaluate the effect the application technique would have on temporal and spatial movement of neonicotinoid insecticides imidacloprid and thiamethoxam through plant tissue. Mature Zinnia elegans plants were treated by either a soil drench of neonicotinoid insecticide or foliar application on a single leaf at approximately the midpoint of the plant height. Caged adult aphids were placed on the underside of leaves at five plant heights. Leaves were collected at various post-treatment times along the primary stem of the zinnia to determine levels of insecticide using commercial ELISA kits. Aphid populations were assessed at the time leaves were sampled. Insecticide was detected in all sampled leaves in the drench treatments. Drench treatments reduced aphid populations at all foliar sample locations. On single leaf treated plants, aphid populations were only reduced at the treated leaf and very little insecticide movement was detected. Results demonstrate that the method of delivery of neonicotinoids can have a significant impact on the biological effectiveness. The lack of significant movement of neonicotinoids following foliar application demonstrate the need to good spray distribution across the target plant. Drench treatments may provide more effective application options than foliar treatments for treating difficult to reach target areas.