![]() ![]() The third factor is the amount of precipitation. In some cases, a compound may be susceptible to wash-off, but its environmental persistence and inherent toxicity to the target pest compensates for the loss of residue, thus delaying the need for immediate re-application. The second factor is the inherent toxicity of an insecticide to the target pest and the persistence of the compound in the environment. Penetration into plant tissue is generally expected to enhance rainfastness of pesticides. Others, like the neonicotinoid insecticides, are systemic and can have translaminar (moves from top surface to bottom of leaf) as well as acropetal movement in the plant’s vascular system (moves from center to growing tips of leaves). Many newer compounds, such as spinosyns, diamides, avermectins and some Insect Growth Regulators (IGR), readily penetrate plant cuticles and have translaminar movement in leaf tissue. Some compounds, such as carbamates, oxadiazines and pyrethroids, penetrate plant cuticles, providing some resistance to wash-off. Some pesticide chemistries, like organophosphates, have limited penetrative potential in plant tissue, and thus are considered primarily as surface materials. First is the plant-penetrative attributes of the various compounds. There are several critical factors that influence impact of precipitation on a pesticide’s performance. In 2006, AgBioResearch provided funds to purchase and install a state-of-the-art rainfall simulation chamber at the Trevor Nichols Research Center (TNRC), after which Michigan State University Extension has conducted trials on fruit crops for a range of insecticides. The rainfall events experienced in Michigan have prompted questions about the relative “rainfastness” of the insecticides used in fruit production. ![]()
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