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Northern Illinois Agriculture

University of Illinois Extension
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Hot, hotter, hottest

Posted by Russel Higgins - Soybeans

Today I managed to get several outdoor projects done in the morning and decided that the afternoon would be a great time to catch up on indoor activities. The fact that afternoon temperatures have inched back up into the upper nineties may have had something to do with my decision. Traveling across northern Illinois this week I am starting to see Spider mite infestations starting to flare in soybean fields.Spider mites can be found in most soybean fields on most years, but it is drought conditions that is most associated with mite economic outbreaks. Hot and dry conditions reduces fungi that normally act as a control for the spider mite population. Drought conditions also make the soybean plant a more attractive food source for the mites. Plant injury takes place when the mites use their piercing mouth parts to remove plant fluids from the vascular system. The feeding results in decreased chlorophyll and photosynthetic activity and can prematurely kill the soybean plant. "Stippling" (small yellow and white dots) followed by bronzing of the leaves are the most obvious symptoms. A rescue treatment should be considered when plants within field margins are showing leaf discoloration and mites are present. Growers should consider a treatment when 20% to 25% discoloration is found before pod set or 10% to 15% discoloration occurs after pod set. Spider mites often start on field edges, if treatment for spider mites is warranted; chlorpyrifos or dimethoate are recommended. I always encourage producers to exit their trucks to scout fields, but on a hot day like today you may want to drive around your soybean fields from the comfort of your air conditioned cab and look for spider mite damage!

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