Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Field Corn
Once again we are seeing a significant increase in the number of Brown Marmorated Stink Bug adults on the edges of some of the field corn fields we are surveying in New Castle County. These high populations are confined to field edges next to woods making treatment very difficult. It will be important to watch for movement of these populations to any nearby soybean fields, especially as the earliest planted fields are entering the pod set stage.
Soybeans
We continue to see a number of defoliators (grasshoppers, Japanese beetles, bean leaf beetles and green cloverworm) present in full season beans. As full season fields enter the bloom to pod fill stages, remember that the threshold drops to 15% defoliation.
We continue to see an increase in stinkbug populations (green and brown) in full season bean fields so be sure to watch for this insect as the earliest maturing fields begin to set and fill pods. In New Castle County, Brown marmorated stink bug numbers have increased from last week, mainly on field edges near woods, but the numbers are still much lower than the native stink bugs. Economic damage from stink bugs is most likely to occur during the pod development and pod fill stages. You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. As a general guideline, current thresholds are set at 1 large nymph/adult (either brown or green stink bug) per row foot if using a beat sheet, or, 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans.
Although the wet weather continues to keep spider mites populations in check we did see an increase in populations over the last week. Be sure that you continue to sample for mites in your routine sampling each week. Early detection and control before populations are exploded is necessary to achieve effective control.
As expected, we are seeing a slight increase in soybean aphid detections since last week so be sure to watch for this insect while checking for other insect pests. As a reminder, there is both a conventional method and a speed scouting method that can be used to make a decision on management for soybean aphid — please see the following link for more information: http://cropwatch.unl.edu/web/cropwatch/archive?articleID=5278671
We continue to survey for Kudzu Bug as well – and as of this week there have been no new detections in soybeans. In VA, they have started to treat a few fields so be sure to continue to watch for this new invasive insect pest. Be sure to check out the Kudzu Bug website – www.kudzubug.org for any new developments. We will also alert you if we see an increase in populations as well as when we find the first nymphs – the important stage for treatment in soybeans.