Field Crops Entomology Program
Michigan State University
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Spider mite info
I have seen mites on the bottom leaves in soy and corn fields, and I've heard reports about heard about mites in soybean, dry bean and beets. Hot, dry conditions favor mites. Rainfall helps, but humidity must remain high under a canopy for at least 48 hours for mite-killing pathogens can take hold. Irrigated fields may actually support huge populations of mites if leaves dries off quickly once the irrigation stopped. Mite outbreaks are also triggered by sprays of most pyrethroids, which kill beneficials but not spider mites. Bifenthrin is the exception - it does not flare mites. Some tips for spraying mites are below.
*Good coverage is critical for control. Use the highest gpa practical; more water is better. Ground is usually better than air.
*Read the label to understand how the chemical acts on mites. Most insecticides kill mites but not eggs; unless the product has longer residual, newly-hatched mites recolonize quickly. Newer mite growth regulators kill eggs and nymphs, but not adults - they act slowly to reduce the population.
*Never apply the same product, or one from a similar group, twice in a field. Switch modes of action to avoid resistance.
*Insecticides which double as miticides (for ex bifenthrin, dimethoate) are hard on beneficials as well as honey bees. During the 2012 drought, several bee kills investigated by MDARD focused on dimethoate use in soybean. To avoid such a situation, check labels for specific warnings and guidelines about application to crops in bloom. Know the neighborhood, and talk to beekeepers in the area (they may be able to cover or move hives). Check the Drift Watch web site for locations of apiaries in Michigan (https://mi.driftwatch.org/map). Spray in the evening vs during the day to avoid exposing foraging bees.
*Note that preharvest intervals range from 0 – 60 days depending on the crop x insecticide.
Western bean cutworm in dry beans
WBC trap catches are peaking in Michigan, with some traps capturing hundreds of moths. For dry bean production in central Michigan and the UP, the 7 to 14 days after a peak are the critical time to consider spraying to avoid unacceptible levels of damage at harvest. The bulletins below provide information on ID, scouting, action thresholds, and spray tips.
NEW Quick recommendation sheet for dry beans