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.