CORN Newsletter: 2005-19, June 28, 2005

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C.O.R.N Newsletter 2005-19
June 28, 2005 - July 6, 2005

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Two-spotted Spider Mites Diagnosis and Control
by Ron Hammond, Bruce Eisley


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If aphids were not enough of a problem for soybean growers, we are now receiving as many calls about two-spotted spider mites (TSSM), a problem we have not seen this early in the summer since 1988 and 1993. The cause of these mite problems is the hot and very dry conditions many parts of Ohio are experiencing. We should note that other Midwest states with similar conditions are also experiencing mite problems.

While sampling your field for soybean aphids, which should be started this week, you should also begin examining plants for two-spotted spider mites. The easiest way to locate mites is to look for telltale signs of their injury, yellow spotting or stippling on the upper side of leaves. Here are two pictures showing this stippling, both on a unifoliate leaf (http://www.ag.ohio-state.edu:8000/~corn/agcrops/images/soybean/TSSM1.jpg) and a trifoliate leaf (http://www.ag.ohio-state.edu:8000/~corn/agcrops/images/soybean/TSSM2.jpg). There are no thresholds available for mites on soybeans. Treatment is recommended when mites become numerous in the field and begin to cause discoloration of the plants, especially the lower leaves. If this damage is not controlled, the result can be the early death of the plant. Growers should also take into account future weather predictions, because we do know that continued hot and dry weather will aggravate the mite problem, while cool and wet weather will tend to lesson it. However, if cooler and wetter conditions arrive, we would still suggest keeping a close eye on this pest.

Although the two-spotted spider mite usually occurs later in the summer, especially along field edges, past experience has suggested that early in the summer, we can often find mite populations in spots across the field. Thus, before field edges alone are sprayed, growers should walk the field to determine if the mites are present throughout. If mites are indeed present across the field, an entire field treatment would be justified.

There are only two materials, which are currently available for mite control on soybeans, Lorsban 4E (chlorpyrifos) at 1 to 2 pt per acre, and dimethoate at various formulations and rates. Of these two, the label for Lorsban states that “When large numbers of eggs are present, scout the treated area in 3 to 5 days. If newly hatched nymphs are present, make a follow-up application of a non-chlorpyrifos product that is effective against mites”. It should be mentioned that Warrior is labeled for mites, although it is for suppression only. Also note that if treatment becomes necessary within the next few weeks, that soybeans most likely will be in the flowering stage, which brings up the same concern mentioned about bees as in the soybean aphid article. Please read the section on spraying during soybean flowering and concerns about bees in the article on soybean aphid.

Readers can subscribe electronically to this newsletter by signing up at http://agcrops.osu.edu/services/email.html. E-mail labarge.1@osu.edu if you have problems subscribing or no longer wish to receive this newsletter.

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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