Two spotted spider mites have been reported in areas of northern Indiana and into Michigan. They are also likely present in other areas of the corn belt that have had similar weather patterns. Hot and dry weather favor rapidly expanding populations of the pest.  Spider mites are very difficult to see with the naked eye.

The first visual indication you’ll notice is discolored/yellowing of leaves along field edges, waterways, roadside etc. Spider mites overwinter in these areas and will rapidly expand into soybean fields when the environment is favorable. You might notice a “V” shaped area of damage moving out into the field where the population is growing. They live on the undersides of leaves and suck the juices from leaf tissue resulting in a burned look or stippling.

To determine if you have an active population, go to the field edges or areas that show the yellowing symptoms. Hold a white piece of paper low in the canopy and shake the plants. Look for tiny dark spots moving on the paper.  You’ll also see faint white webbing on the underside of leaves.

Before deciding whether or not to spray a rescue treatment, you need to look at the weather forecast.  A good rain shower will do wonders for controlling them! Not only does it wash them off, so to speak, but the moist environment encourages development of beneficial fungi and other bugs that pray on the mites. If you have a 7- to 10-day forecast of continued hot and dry, it’s time to take action. If caught early enough, you might be able to get away with just spraying field edges. If your scouting has found them more widely, spread a whole field treatment is best.

There is limited information from universities on economic thresholds. In heavy infestations yield loss will be significant. The rule of thumb is if you’ve identified an expanding population and the weather is favorable for that to continue, then spray. It’s recommended to use a full rate of an organophosphate-based insecticide as they have great control of spider mites and aren’t detrimental to beneficial mite predators.

If you have any question or want assistance in diagnosing a field, please contact one of your local LG Seeds SAM or TTA.

Additional Information:
https://extension.entm.purdue.edu/fieldcropsipm/insects/soybean-spidermite.php
http://corn.agronomy.wisc.edu/Management/pdfs/A3890.pdf

Note: The information in this issue is based upon field observations and third-party information. Since variations in local conditions may affect the information and suggestions contained in this issue, LG Seeds disclaims legal responsibility therefore. Always read and follow label instructions. LG Seeds and design are trademarks of AgReliant Genetics, LLC.

Download a copy of this Technical Bulletin: Tech_391 - Two Spotted Spider Mites