Where much of the cotton crop is pretty much bug-safe, much of the Virginia soybean crop is in the most vulnerable growth stage, R5-early R6, to corn earworms and stink bugs. Both of these pests have a preference for the tender, developing seed (the R5 stage) and many fields are in or near that stage. The good news is that for the most part, corn earworm and native stink bug populations (green stink bug and brown stink bug) seem to be pretty light and spotty. Most reports are in the 1-3 worm/15 sweep range, certainly not excessive pressure, and the moth flight seems to be in decline. Native stink bug infestations are also very light to the point that and we cannot locate any field with a lot of native stink bugs. Although many growers have or are treating fields, if scouted, they are seeing that many fields are not at thresholds. We sometimes have another late summer/early fall corn earworm flight which could result in some new worm infestations, but it if this does happen, most fields will be in the bug-safe late R6-R7 stage.
A problem still exists with our adult pyrethroid vial test results. Last week’s sample reached 58% survivors, the highest level ever recorded for Virginia, and this week’s early sample was still at 50% survival. We have at least one report of lack of control in a soybean field treated with a pyrethroid (no need to mention any product names). If you are choosing a new product, a ‘brand’ you are not familiar with, be sure to check the label to see what you are buying/spraying. There are some products that are a mix of two pyrethroids (no help if you are concerned about pyrethroid resistance).
The problem story is with brown marmorated stink bugs. The more we look, the more we find. We are just now getting our scouts into the high risk counties in the northern and central areas. The reports show that many soybean fields in those counties (including Rockingham, Culpeper, Stafford, Madison and Orange Cos.) are infested at levels that need to be controlled. We do not have good thresholds or good sampling techniques for brown marmorated stink bug. It is almost impossible to get a good sample with a sweep net because they startle easily and drop to the ground quickly. But we do have data from last year that shows how damaging they can be to soybeans in the infested areas. The best we can offer now is that if you can visually ‘see’ several bugs on the upper leaves, there are MANY more down in the canopy feeding on seed. Like last year, field edge treatment seems to be all that is needed as the bugs are staying in the first 50 or so feet of the field edge. Edge treating (one spray boom width) was effective last year, and we are working to document the outcome (hopefully success) of this strategy again this year.
Kudzu bugs have not been reported in any new counties since our last pest advisory, but we do have reports of some egg masses in a couple of locations. We will likely see some nymphs soon in some fields, but time will tell if we get into any treatment situations. The later nymphs occur the lower the risk that they will develop into high populations, or that they will be able to cause any appreciable damage to plants. More next week as we progress with our scouting effort.