David Owens, Extension Entomologist, owensd@udel.edu and Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
Soybean
We continue to see bean leaf beetle, grasshopper nymphs, and bean leaf rollers in soybean fields. This week we started picking up early instar green cloverworm. All of these insects contribute to the defoliator guild, and by themselves rarely cause problems. Very high densities of green cloverworm, several per row foot, are necessary to significantly defoliate soybean. Some entomologists consider them almost beneficial because they provide a good food source for predatory insects.
A couple of really early soybean fields are starting to flower, and green stink bugs are starting to move in in very low numbers. Recently, VA and NC raised thresholds to 5 bugs per 15 sweeps once beans hit R4. It is unlikely that these early fields will develop large enough stink bug populations. Green stink bug populations peak in late summer/early fall. We are also beginning to see spider mites moving into soybean fields. Small hotspots can be found in a few fields. Look underneath leaves for stippling and for sand that is sticking to the leaf, caught in the spider mite webbing.
Field Corn
We discussed management concerns of stink bugs in field corn in an article in last week’s WCU. There are two other points worth mentioning. First, wheat is a favored host for brown stink bugs to produce their first generation. Sweeping wheat adjacent to your corn may give you an idea of the potential stink bug threat to the corn once wheat is harvested. The second is that, at least in southern states, the most common species in corn is the brown stink bug which shows up on the edges first. If you sample routinely along the edge 50 feet of a field and do not see any stink bugs, it is less likely that they will be present in the field interior.
Wheat field adjacent to field corn; a scenario which has the potential for brown stink bug invasion into the corn.