percentages—implications for treatments in soybean
At the time of this report, we have tested 109 corn earworm moths this week. These moths represent the ‘front edge’ of the large second generation flight from corn. The results are not good. The first batch of 49 moths had 49% survivorship and the second batch of 60 moths had 53% survivorship. We have another 150 moths in vials to be assessed tomorrow (Friday). What does this mean? This confirms what I thought we might see based on previous year’s patterns—with survivorship percentages peaking in late July/early August. If corn earworm flights are heavy and large worm infestations set up in soybean fields, non-pyrethroids will need to be tank-mixed with pyrethroids (which are still recommended to control whatever stink bugs may be present). We have had success with several pyrethroid tank mix options including with Belt, Steward, and Orthene. I was asked about Lannate. Lannate is an effective product against corn earworm but I have not tested whether it will tank mix with a pyrethroid. If you choose this option, you should jar-test the mix before loading your spray tank. Also, although effective, Lannate has a very short residual activity period—24 hours, unless it rains. If the worm infestations do not develop to high levels, the pyrethroids will probably still do a decent job—apply them only at the highest labeled rate.

Below is an advisory provided by Bill Shockley, Virginia Coop. Extension Ag Agent in Northampton County (southern most county on the Del-Mar-Va Peninsula). This is a traditional vegetable and potato growing county so insect pests are often different from what we find on the ‘mainland’. But Bill’s comments are insightful. And, we also have reports of some beet armyworm infestations in Virginia Beach soybean fields

From Bill Shockley: We are finding a large number of beet armyworms in young soybeans in Northampton County, Virginia. They are especially prevalent in soybean fields planted double crop after potatoes, string beans and other spring planted vegetable crops. These insects are foliage feeders and will severely damage leaves and stems of young soybean, lima bean and string beans plants. Traditional spray applications of pyrethroid insecticides have been generally ineffective in the past for controlling these pests. Labeled applications of Steward, Belt or Lannate have provided the only significant control of these insects.

We are also beginning to find generally low numbers of corn earworms in soybeans in some areas. As soybeans begin to blossom, and pod formation begins, these insects will become more of an economic problem in this crop.

It is vitally important to begin scouting for these insects at this time. The timing of chemical control applications for these pests is very important to assure maximum control and limit unnecessary production costs.

We are getting a few calls about spider mites in soybean. Following is an update from Dr. Joanne Whalen at University of Delaware that covers management and control. This is a very well done summary that addresses a lot of the issues regarding product choices, their strengths and weaknesses and other very valuable information.

Dr. Whalen: With the extended drought conditions in our area, we continue to find significant populations of spider mites in both full season and double crop fields as well as in irrigated fields. In most cases infestations are field wide so edge treatments will not be effective. As we learned in past years, drought will seriously stress plant growth, favor mite development and create plant growth conditions that make it difficult to achieve effective control. Early detection, rotation among available control options and multiple applications are often needed under drought stress conditions. Under high population pressure, a single treatment is often not adequate to kill all the life stages. Mite eggs will not be affected by the initial knockdown/control of adults and nymphs and thus hatch after a few days. The only available materials for spider mite management in soybeans in Delaware are dimethoate, Lorsban (as well as generic chlorpyrifos products), bifenthrin (numerous generics available) and Hero. (Be sure to read all labels before spraying for restrictions and rates). Unfortunately, we do not have a selective miticide labeled for soybeans like we do in vegetable and fruit crops. The following is a summary of what we have seen so far this season as well as a summary of results from past seasons.

Hero and bifenthrin Products – A number of products containing the active ingredient bifenthrin are available for spider mite management in soybeans . Some examples include Brigade, Bifenture, Frenzy and Sniper. In addition, Hero, a combination product including both bifenthrin and zeta-cypermethrin (two pyrethroids) is also available. In many cases, these materials have provided good initial control but a second treatment has been needed, especially if populations were exploded at the time of treatment and numerous mite eggs were present. Early detection and control is needed as with all of the materials available for mite management in soybeans. In addition, most of the labels for products containing bifenthrin state “: “do not make applications less than 30 days apart or do not apply more than once every 30 days“. Therefore, you will need to rotate to a material with a different mode of action if a second application is needed.
Dimethoate – In past years, dimethoate has not provided effective spider mite management under drought stress conditions. However, this year we have received reports of fairly good control in some situations but it should be noted that rain was received in those areas. Although dimethoate is the only systemic material available for spider mite management in soybeans it must be absorbed and translocated by the leaf tissues to provide residual action; otherwise, it undergoes rapid photodecomposition from sunlight. This leaf absorption process is greatly reduced in drought-stressed plants that have “shut-down” physiologically. Another important factor that plays a role in the performance of dimethoate is the pH of the water used as the carrier. Many pesticides, especially dimethoate, are subject to breakdown by alkaline hydrolysis. (http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/ICG_08/01_Intro_08.pdf) In alkaline water (high pH), there is a break in certain bonds in the dimethoate molecule, causing two or more new molecules to form. This increases the decomposition rate of the insecticide and can result in poorer than expected field performance. Dimethoate degradation is also accelerated by the mineral content of the water, especially the presence of iron. If a high pH situation exists, you can lower the alkalinity of the water in the spray tank by adding an acid-based buffer. An important consideration is to select a buffering product that lowers the pH to the acid range without causing phytotoxicity. Also, the buffer must be added to the spray tank first, before the addition of dimethoate.
Note – the dimethoate label states it has a “ 7 day reapplication interval. “
Lorsban (chlorpyrifos)- We have seen good initial control of mites with Lorsban and other generic chlorpyrifos products this season. A second application with another material has been needed especially if populations were exploded at the time of treatment and numerous mite eggs were present. Lorsban ( and other generic chlorpyrifos products) can provide good contact control of motile mites when applied in enough water to get good coverage. Since Lorsban is not a systemic product, a second spray of non-chlorpyrifos product may be needed in 5 to 7 days to kill newly hatched mites. The Lorsban label states that: (1) When large numbers of eggs are present, scout the treated area in 3-5 days and if newly hatched nymphs are present, make a follow up application with a non-chlorpyrifos product and (2) do not make a second application of Lorsban 4E or other product containing chlorpyrifos within 14 days of the first application. So before applying any material, be sure to read the label for rates as well as all restrictions including but not limited to the total number of applications allowed, rotation between materials, minimum number of days required between applications as well as the pre-harvest interval between last application and harvest. Spider mite management is never easy under drought stress conditions. Early detection and multiple applications of materials with different modes of action are often needed to reducing losses from this pest in soybeans. As a reminder, under heavy mite pressure and extended hot, dry weather, it often takes an extended period of free moisture on leaves, high humidity during the day and cool evening temperatures to get an increase in the fungal pathogens that can significantly reduce exploded mite populations.

We have found kudzu bugs, adults only, in three new counties, Pittsylvania and Henry Counties (in kudzu only) and Dinwiddie County (in soybean). These adults are the second generation. Adults are active and can fly long distances. The first generation developed to the south of us in either soybean or kudzu. We can expect more fields to become infested over the next several weeks and there is no way to predict for sure where these will be. I think most of our soybean acreage in Virginia could be at risk. The best way to sample for kudzu bugs is with the standard 15-inch diameter sweep net. Sweep the edges of fields first as they typically start there. Also, they seem to have a preference for beans that are flowering. If you find adults, don’t panic. The thresholds developed in the southeast are based on the capture of nymphs—an average of 1 nymph per sweep—so 15 nymphs in our recommended 15 sweep sample. Adults invade fields, lay eggs, and the nymphs hatch to begin feeding. So by waiting to make a treatment until nymphs are present means the insecticide will have the best chance of killing all stages and lasting—hopefully a single application. Spraying when adults, only, are present will most likely result in having to make a second application. Begin sweeping field edges, especially fields with flowering plants—and please report any catches to us so we can keep track of the occurrence and spread.

Brown marmorated stink bugs are slow to develop this year. I think this could be related to the extreme heat—they just don’t seem to like hot weather (don’t quote me on that). But we are not waiting. We started our survey program this week and a scout reported finding a few on the edges of one or two fields in Orange County, one of the areas that was hit hard last summer. We are going to increase our survey effort over the next few weeks and post all findings on this advisory.

Our field corn survey is not completed, but so far, most counties that have reported are indicating pretty high percentages of infested ears (50-60 percent in the southeastern counties). If conditions stay dry, we may have a pretty heavy flight into soybean fields. Adult moth trap catches are down this week—the quiet before the storm. We had a small flight earlier which resulted in a few worms in whorl-stage sorghum and an occasional worm in cotton and soybean fields, but this next flight from corn will be the big one. Because corn fields are variable in condition and maturity, the moth flight will most likely be sporadic and localized—heavy in some areas, lighter in others. The only way to determine if fields are infested worms is to scout them, especially once pods start forming. We will post weekly updates as more information comes in.

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.