Drip-Chemigation with Imidacloprid and Nematodes for Control of Scarab Larvae in Nursery Crops

Authors: Reding, Michael - Mike; Zhu, Heping; Derksen, Richard

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2008
Publication Date: 7/30/2008
Citation: Reding, M.E., Zhu, H., Derksen, R.C. 2008. Drip-Chemigation with Imidacloprid and Nematodes for Control of Scarab Larvae in Nursery Crops. Journal of Environmental Horticulture. 26:93-100.

Interpretive Summary: The larval stages of exotic scarabs, also known as white grubs, damage nursery crops by feeding on their roots. Managing these insects is difficult because they live in the soil making them hard to detect and reach with insecticides. Treatments of insecticides are usually applied to the soil surface then followed by applications of water to leach them down to these insects. Applying insecticides through drip irrigation systems helps alleviate the need for extra applications of water. In addition, this technique applies the insecticides more accurately to the target area reducing drift and reduces exposure by workers to insecticides. We applied insecticides and a biological control agent (nematodes) through drip irrigation for control of white grubs. We also tested two other application techniques, soil injection and drenching, for the nematodes. Our insecticide treatments reduced the numbers of white grubs in nursery trees by 85%. In addition, we significantly reduced the numbers of grubs with all of our nematode treatments. These results show that insecticides applied through drip irrigation systems can be effective controls for white grubs in field-grown nursery trees. Furthermore, we demonstrated that nematodes in combination with low rates of insecticides were similarly effective. This information should help nursery growers to better manage white grubs, while reducing worker exposure to pesticides and saving on fuel costs related to spraying with a tractor.

Technical Abstract: Larvae of exotic scarabs, also known as white grubs, are subterranean insects that damage ornamental nursery crops when they feed on the roots. Management is generally based on application of chemical insecticides to the soil surface, followed by supplemental water to leach the toxicants into the soil. Drip irrigation systems have the potential to deliver insecticides and insect pathogens to the root zones of crops to control subterranean insects. Benefits of this delivery system are reduced worker exposure to insecticides, reduced labor, and the potential to concentrate the control agents in the target area. During 2004 through 2006, we tested the efficacy of imidacloprid (2004-2006), clothianidin (2006), or entomopathogenic nematodes (EPN) + imidacloprid (2005) applied through drip irrigation for control of white grubs in an ornamental nursery. Insecticides (imidacloprid or clothianidin) or EPN + imidacloprid were injected into drip irrigation lines at the upstream end of rows in a commercial nursery. EPN + imidacloprid was also injected into the root zone of trees or applied as a surface drench. In 2004 and 2005, imidacloprid applied at a preventive timing through drip irrigation lines significantly reduced the numbers of white grubs in the root zones of Kousa dogwood (Cornus kousa Hance) trees. In 2006, variation in the data resulted in no significant differences at the P = 0.05 level, although, the percentage reductions of grubs by imidacloprid and clothianidin applied through drip irrigation were similar to trials in 2004 and 2005. EPN + imidacloprid applied through drip irrigation, injected into the soil, and surface drenched at a curative timing all significantly reduced the numbers of grubs compared to untreated trees. These data indicate drip irrigation is a viable delivery system for controls of white grubs in nursery crops.