As soybeans approach the critical pod-filling and yield-determination stages, many areas of the U.S. are experiencing increased insect feeding in soybeans. Two pests that are currently dominating this year’s soybean crop are Japanese beetles and two-spotted spider mites.
The two-spotted spider mite is beginning to make an appearance in areas with continued dry weather. Proactive scouting is important with these mites. If the golden-stippled damage can be observed from the road, it is too late. Mites typically reside in the grass along the roadside and waterways. The first thing growers should consider when under dry conditions is to stop mowing and force the spider mites into their bean fields. Dry weather exacerbates spider mite problems because their rate of reproduction increases, fungal predators decline and their host plants often die or dry up, making the soybean plant a more succulent host.
Begin by scouting the edges of fields or along grass waterways to monitor for the pest, but also make sure to walk into the field to scout for their presence deeper in the crop. Although it is difficult to come up with a true threshold, some universities suggest that if stippling is observed on the lower leaves and spider mites are present the middle canopy it may be time to consider treatment. Don’t assume all insecticides are equal. Be sure to consult with your agronomist for treatment recommendations. It is also important to continue to scout after treatment as it is possible that fields can repopulate if coverage into the canopy is not adequate. Utilizing new spray technologies that can increase canopy penetration may help increase the effectiveness of the treatment.
Japanese beetles are also feeding in soybeans, creating the window-pane effect that leaves the veins intact while removing the leaf tissue. Like the two spotted spider mite, Japanese beetles can be more present around the field’s edges, so be sure to scout the entire field. Examine multiple areas of the field and look at 10 trifoliates at each stop from the upper, middle and lower part of the canopy for injury. Although treatment for Japanese beetles and other defoliators such as the bean leaf beetle are not exceptionally common, if defoliation reaches 20-20% during the reproductive phase treatment may be warranted. Consult your local agronomist for defoliation guides treatment recommendations.