Indiana Prairie Farmer publishes a column written by Tom Bechman with the help of CCAs for CCAs and their clients. With permission from Prairie Farmer we are posting these Soybean and Corn Pest Beat articles on the CCA website. Many thanks to the authors and the support of Indiana Prairie Farmer.
Soybean Pest Beat Articles
Drought conditions? Look for spider mites
The Indiana Certified Crop Adviser panel includes Betsy Bower, Purdue Extension senior research associate, West Lafayette; Abby Horlacher, Nickel Plate Consulting, Sheridan; and Brian Mitchem, Farmer 1st Agronomy Consulting Services, Decatur.
We’ve had a dry stretch in my area this year, and I spotted some spider mites in one of my soybean fields. What is the threshold for treatment? How can I control them? Will the treatment last or do I need to follow up?
Bower: Scout for spider mites by shaking the upper part of the soybean plant over a white piece of paper and then looking for small, orange mites on the page. Treat if you find active spider mites, notice leaf discoloration and see that the forecast shows prolonged dryness. Even if you stop spider mites with a miticide, you will not regain much green tissue in the damaged plant.
One of the most effective tools for spider mites is the active ingredient dimethoate. But there are years when product can get short due to widespread use. There is at least one pyrethroid bifenthrin with good activity, too. See your local ag retailer for guidance on rates and timing. New on the market is Zeal SC and Stifle SC.
Horlacher: Spider mites can become a serious issue in soybean fields during hot, dry weather because populations reproduce quickly under plant stress. According to Iowa State University and Purdue University, treatment should be considered when mites are moving into the middle canopy and yellowing or stippling is increasing across most of the field. Once mites reach the upper canopy and leaf drop begins, yield loss is already occurring.
Product selection is important because some insecticides are ineffective on mites and can worsen infestation by eliminating beneficial insects. Pay attention to the label to know if your pesticide works on spider mites. Thorough canopy coverage is critical since mites feed on the underside of leaves. Fields should be scouted seven to 10 days after application because populations can rebound during continued hot, dry conditions.
Mitchem: Spider mites can have a significant impact on soybean yield. If present, they should be managed with chemical control products. Mites reproduce and spread with wind very quickly under drought conditions. Applications should be made as soon as possible when you first observe the initial leaf bronzing from mite feeding. Apply several additional passes from the impacted field border to help control the population that has likely moved further into the field. Populations typically start on the border, but you may also see them start on light, sandy soils within fields.
There are several products that are effective on mites. Bifenthrin and dimethoate are commonly used products for knockdown and residual. Newer products such as Abamectin and Stifle/Zeal Pro are also effective and offer newer sites of action.
