It may be happening for the first time that I can recall—a late season infestation of corn earworms in soybeans. The last couple of nights we have trapped more corn earworm moths (about 1800 and 1500, respectively) in our pheromone traps than we have ever captured. These are alarmingly high numbers and I am getting reports that folks are seeing a lot of moth activity in and around fields of cotton, soybean and peanut. I got the first report today that some growers in southern Southampton County are having to retreat some soybean fields. I have been telling folks that as best I can remember, I have never seen a ‘new’ infestation of earworms develop in September. Well, as one of my earlier mentors said to me one day. “Don’t make predictions about insects. They’ll make a liar out of you every time.” Seems he was right. So, what crops are at risk? The cotton and peanut crops are safe as we are close to defoliation time with cotton and digging time with peanuts. Only late planted soybean fields that still have susceptible pods (earlier than R7 growth stage) are at risk. The good news is that our corn earworm pyrethroid vial test results have been showing a gradual decrease in the percent of moths surviving (see the attached graph) to levels below 10%, which means that pyrethroid insecticides should provide good control, relatively inexpensively. If I was someone’s mentor, I would want to go down in history as saying, “Never let your guard down. Never stop checking fields for insect pests until the crop is mature.”
Additional information: cew-avt-graphs-sept-8-2011-pdf

The brown marmorated stink bug (BMSB) which was first identified in 2001 in Allentown, PA, is now infesting soybean fields in parts of Virginia. This stink bug, although similar in appearance to our native brown-colored species, can be easily distinguished by the white bands on their antennae, and the white bands on the legs of nymphs. BMSB is a known pest of many crops, wreaking havoc on fruit crops, wine grapes and many vegetable crops, especially sweet corn. Although the ‘epicenter’ for this pest is still the mid-Atlantic region (PA, DE, MD, VA and WV), a few have been found in states as distant as California.

BMSB, like our native stink bug species, feeds directly on developing soybean pods and seed. If the damage occurs very early in seed development, pods will be flat and brown, but still be attached to the plant and easy to see. If damage occurs later in seed development, pods will appear yellow and speckled, and opening the pod will reveal damaged, crinkled, stained seed.

Last summer (2010) we began a monitoring program for BMSB in soybean and found them in soybean fields in 15 Virginia counties, but always in low numbers. In Maryland where they had seen these same kinds of low numbers the previous year (2009), last summer (2010) they found large infestations on field edges. The same pattern has occurred for us. This summer (2011) we have found several fields with very high numbers. So far, the heavily infested fields are confined to one geographical area—the north-central piedmont counties of Orange, Culpeper, Madison, Fauquier and Clarke. Very low numbers have been reported in other counties.

A pattern seems to be emerging that is playing well for us in terms of managing BMSB in soybean. To date, yield threatening infestations seem to be confined to field edges, not going beyond 30 to 50 feet into the field. Heavy infestations also seem to be associated with fields with wooded borders, especially if there are concentrations of the invasive weed, Tree-of-Heaven (Ailanthus altissima). Both BMSB and Tree-of Heaven are native to China and other parts of Asia. BMSB seems to be strongly attracted to that host, especially when the trees are putting out their seed clusters. Not coincidently, the north-central piedmont area where we are finding the highest densities of BMSB in soybean is the area with the highest concentration of Tree-of-Heaven. I encourage you to ‘Google’ Tree-of-Heaven and become familiar with what it looks like.

This strong field edge effect has made it possible for our local soybean growers to make edge treatments applying insecticides in one spray-boom width around a field, without having to treat the entire field. We are revisiting as many of these edge treated fields as often as we can, and so far, the edge treatments are holding. Another bit of good news is that many of the insecticides commonly used in soybean are effective against BMSB. This summer, we were able to put out three insecticide trials in growers’ fields in Orange County and most of the products we applied worked very well (including Baythroid XL, Belay, Brigade, Cobalt Advanced, Endigo ZC, Lannate LV, Orthene 97, and Vydate L). The problem for fruit growers is not that they cannot kill these critters, it is that they continue to reinvade their orchard which necessitates repeated sprays. Will this also occur in soybean fields? We are not certain.

How should growers react to this new pest? We are recommending that growers stay vigilant until the latest planted fields reach the R7 growth stage when beans would no longer be susceptible to stink bug feeding. Scout field edges, especially fields with wooded edges with clusters of Tree-of-Heaven. Use a sweep net to sample the plants by making successive 15-sweep samples. We have no exact threshold, but suggest that greater than an average of 4 adults or nymphs per 15-sweeps would constitute a risk to the pods and seed. We have encountered fields with 8 to 10 per 15 sweeps, and in some extreme cases, more than 20 to 30 per 15 sweeps.

So, the bad news is we have another established insect pest of soybean in Virginia. The good news is we have already made some progress in terms of how best to manage it. As a final note, we are also in the process of doing field cage studies to determine 1) how damage by BMSB may differ from damage by our native stink bug species, and 2) what a damage threshold might be—more on this later.

The BMSB situation has not changed a lot since last week, except that we have found them in a couple of ‘new’ counties. Our epicenter for high populations is still in the north/central part of the state (see the attached distribution map). Several growers in that area have applied field edge treatments and we are in the process of doing as many follow-up visits as possible to determine if/when the bugs may move back in. So far, edge treatments seem to be holding and we ARE NOT recommending treating whole fields. These BMSB infestations have been very consistently on field edges so spraying entire large fields appears to be a waste of time and money. What can we expect in the next few weeks? Will BMSBs move into late planted fields, a pattern that we often see with our native stink bug species? Or, will BMSBs begin to leave fields for their overwintering sites in buildings and structures? We are not certain. Our plan is to keep monitoring as many fields as possible through the end of September when most fields would be developed to a stage that is safe from stink bug damage. We also expect to see fields, especially in the north/central part of the state, with stay-green syndrome on the edges—a response soybean plants have to stink bug damage that occurred earlier in the season. Finally, we are still monitoring our field insecticide trials and although these are not finished, we are seeing good results with most of the products we applied. We are seeing good control with several products including Vydate, Lannate, Belay, Baythroid XL, Endigo ZC, Cobalt Advanced, and Brigade. More details will be provided once these tests are completed.
Additional information: va-bmsb-soybean-sept-1-2011-pdf

I have attached a new map of Virginia showing the counties where we have encountered BMSBs in soybean fields. A difference from last year–many of these fields have heavy infestations on the edges. At this point, some of the growers have made edge treatments, one spray boom width, to see if this will stop the infestation. Our challenge now is to try to begin revisiting at least some of those fields to determine if this strategy has worked, and if or when infestations may recur. We now have some post treatment ratings on several insecticides and most are providing good knockdown. We were able to evaluate only a few of the products available, but may have more opportunities later in the season. To date, we are getting good control with Lannate, Vydate, Cobalt Advanced, Belay, Orthene 97, Endigo ZC, Baythroid XL, and Brigade. We will provide more details as we have time.
Additional information: va-bmsb-aug-25-2011-pdf

Thanks to the conscientious effort of our field scout, Ed Seymore, we have located several soybean fields in Orange County, Virginia (about 20 miles NE of Charlottesville) with large numbers of brown marmorated stink bugs. These high density areas are very much restricted to field edges next to woods, especially where there are groups of tree or heaven. On these field edges we could easily capture 10 to 20 adults and nymphs, or more, in a 15-sweep sample. The ratio of adults to nymphs was heavy on the nymph side, with evidence of old egg masses on the leaves. As best we could determine these infestations went only about 30 feet into the fields, then numbers dropped to 1 to 2, or less per 15 sweeps. There was evidence of feeding with flattened pods and discolored pods with damaged seed. There is no question that these infested areas will suffer from ‘stay green’ syndrome at the end of the season. We are not sure how widespread this problem is, but are doing what we can to locate other problem areas/fields. So far, we have no other reports. In one field, we were able to put in a couple of fairly primitive insecticide efficacy trials. I use the word primitive because we had to ‘fit’ plot plans into these narrow field edges with their curves and ups-and-downs (not much flat ground in that part of the state). We hope to take post treatment ratings soon and will post results, if we are successful.

There are more reports this week of soybean fields nearing or reaching thresholds for corn earworm, but the situation is sill spotty. We have checked a lot of fields and are finding essentially none. Other areas seem be trending towards just below, at, or just above thresholds. And there seem to be a few fields with well above threshold numbers. This fits the pattern for a year that I would describe as—normal or average. Moth catches are fairly low in number, steady, or even dropping in some locations. Many are reporting that they are finding higher populations of worms in flowering fields, which would be the double crop, later planted fields. The full season fields or those planted to Group 4 varieties are having less pressure, as those fields are more mature and less attractive to the invading moths. I still maintain that control should be good with high pyrethroid rates, even given the vial test tolerance results. But those fields with high numbers should be treated with non-pyrethroids. Stink bugs are certainly out there, but no major problems have been reported.