Uptake and effectiveness of systemic insecticides as influenced by application technique

Authors: Derksen, Richard; CANAS, LUIS - The Ohio State University

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/15/2012
Publication Date: 7/15/2012
Citation: Derksen, R.C., Canas, L.A. 2012. Uptake and effectiveness of systemic insecticides as influenced by application technique. Symposium Proceedings. In Proceedings of the Ohio Floriculture Association, July 15-17, 2012, Columbus, Ohio. 2012 CDROM.

Interpretive Summary: Consumers prefer clean and blemish free ornamental plants in their homes, work space, and landscape. However, previous studies have discovered that it is extremely difficult to protect all parts of ornamental canopies from infection or infestations. Greenhouse experiments were designed to evaluate the effect the site of application would have on movement of the systemic insecticides Imidacloprid and Thiamethoxam through plant tissue and on insect efficacy. The advantage of using insecticides with systemic activity is that they can be moved through the plant system which can result in better chance of protecting more of the plant. Mature, single stem, Zinnia plants were treated by either a soil drench of insecticide or foliar application to a single leaf at approximately the midpoint of the plant height. Four caged adult aphids were placed on the underside of leaves at five plant heights. Plant leaf samples and insect counts were made two hours, three days, and ten days following treatment. Soil applied drench applications of both insecticides reduced aphid populations at all foliar sampling locations. Both insecticides were detected in all sampled leaves treated by soil application. On single leaf treated plants, aphid populations were only reduced at the treated leaf and very little insecticide movement was detected throughout the rest of the plant. Thiamethoxam was detected more quickly in the leaf samples than Imidacloprid which could help keep insect populations from growing and expanding too quickly. These results demonstrate that the site of application can have a significant impact on the effectiveness of an application. Soil applied drench treatments may provide more effective application options for growers than foliar spray treatments while reducing the amount of pesticide required to produce the ornamental plants and overall costs of production.

Technical Abstract: The use of systemic neonicotinoid insecticides such as Imidacloprid and Thiamethoxam have been shown to be effective against different types of insects including sucking insect like aphids, whiteflies, scales and mealybugs. The most common forms of application of these neonicotinoid insecticides have been sprays or soil applications. The overall goal of this project was to evaluate the efficacy and movement of Imidacloprid and Thiamethoxam when applied separately to Zinnia plants as spray or soil applied drench to manage green peach aphid. Foliar spray treatment was made by using a hand-held sprayer to treat a single leaf at approximately the midpoint in the height of the plant. Four adult aphids were caged to the underside of each of five leaves on a single-stem Zinnia plant at the 10-leaf stage. One-third of the plants received no treatment, one-third received a spray treatment and one-third received a drench soil application. Live insect counts and eight leaf samples were collected a three times: two hours, three days, and 10 days following treatment from each Zinnia plant. Insecticides were detected in all leaves taken from plants treated with the soil applied insecticide. Insecticides were detected in the leaf sprayed in the single-leaf treatments but very little insecticide was detected at other sampling points along the plant stem. More insecticide was detected in leaves above the sprayed leaf than below it. Soil applications of Imidacloprid and Thiamethoxam successfully reduced insect populations at all sampling points along the plant stem. The spray application only reduced aphid populations on the leaf that was treated for each insecticide. The movement of Thiamethoxam was detected more quickly following treatment than the movement of Imidacloprid which could help keep insect populations from growing and spreading too quickly. Because it is difficult to protect all plants in ornamental cropping systems using spray treatments, soil applied drench applications may provide more effective control options.