Implications for pesticide delivery and insecticide selection using chemical analysis of plant tissue and efficacy

Authors: Derksen, Richard; CANAS, LUIS - The Ohio State University; Ranger, Christopher; Reding, Michael - Mike; OZKAN, H - The Ohio State University

Submitted to: Aspects of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2012
Publication Date: 1/10/2012
Citation: Derksen, R.C., Canas, L.A., Ranger, C.M., Reding, M.E., Ozkan, H.E. 2012. Implications for pesticide delivery and insecticide selection using chemical analysis of plant tissue and efficacy. International Advances in Pesticide Application --Aspects of Applied Biology. 114: 279-286.

Interpretive Summary: Research and practical experience have demonstrated that deliverying insecticides through a canopy to reach pests that live at the bottom of the canopy and on the undersides of leaves is difficult. Systemic insectides are sometimes chosen to aid in pest management because they can travel through the vascular system of a plant and can help provide control on in difficult to reach parts of the plant canopy. Experiments were designed to evaluate the effect the site of application would have on movement of imidacloprid through plant tissue and on insect efficacy. Mature Zinnia elegans plants were treated by either a soil drench of insecticide or foliar application on a single leaf at approximately on the midpoint of the plant height. Caged adult aphids were placed on the underside of leaves at five plant heights. Drenches reduced aphid populations at all foliar sample locations. Plant tissue samples and insect mortality evaluations were made 0, 3, and 10 days following treatment. Insecticide was detected in all sampled leaves in the drench treatments. On single leaf treated plants, aphid populations were only reduced at the treated leaf and very little insecticide movement was detected. Results demonstrated that the site of application can have a significant impact on the effectiveness of an application. Applications made from above the top of the canopy to treat lower in the canopy may not be effective even if using systemic insecticides. Drench treatment may provide better insect control and more cost-effective application option than foliar treatment for treating difficult to reach target areas.

Technical Abstract: Applications studies have demonstrated the difficulty in uniformly delivering pesticide across and through plant canopies. Systemic insecticides are often used for management of insect pests because their movement through a plant can provide protection in difficult to treat parts of plants. Insects feeding on the plant may be affected by the insecticide as they feed on the plant. Non-plant feeding beneficial insects remain unharmed. Systemic insecticides may be applied to the soil to be taken up by the roots or to plant tissue above the soil. A series of experiments were designed to evaluate the impact the site of application would have on movement of two common ornamental systemic pesticides through plant tissue and on insect efficacy. Separate experiments were conducted using Imidacloprid and Thiamethoxam as the test insecticides with systemic properties. Mature Zinnia elegans plants were treated by either a soil drench of insecticide or foliar application on a single leaf at approximately on the midpoint of the plant height. Caged adult aphids were placed on the underside of leaves at, above, and below the midpoint of the height of each plant. Aphids were also caged on leaves at similar locations on untreated control plants. Insect counts and leaf sampling were conducted on plants 0, 3, and 10 days after treatment. Leaf samples were processed and the amount of insecticide found in the ground samples were quantified using ELISA techniques on a microplate reader. Drenches reduced aphid populations at all foliar sample locations. Insecticides were detected in all sampled leaves in the drench treatments. On plants with a single leaf treated, aphid populations were only reduced at the treated leaf. Very little insecticide movement was detected in plants that had only a single leaf treated. Over the 10 day evaluation period, higher levels of insecticide tended to be found higher in the plant canopy. Results demonstrate that the site of application can have a significant impact on the effectiveness of an application. Drench treatment may be a more effective application option than foliar treatment but it will depend on the compound and the overall effectiveness of the foliar application. Foliar delivery of insecticides with systemic activity will not guarantee the desired control, especially lower in a canopy that is difficult to reach with conventional application techniques.