We are finding threshold levels of bollworms (eggs and live worms) in conventional cotton (no Bollgard2 or Widestrike). Those fields should be managed using the old system (treat at egg threshold and retreat in 5-7 days). The best approach for Bollgard2 and Widestrike cotton is the treat one time 5-7 days after the egg threshold, which targets any escaped worms. Not treating Bollgard2 or Widestrike cotton could be a mistake. For the past 2 years, we have seen as much as 2-3% boll damage in some Bollgard2 varieties, and as much as 10% damage in one Phytogen variety. A single pyrethroid application (highest labeled rate) cleaned up the problem. One cautionary note, we have gotten reports of worms escaping pyrethroid treatments in cotton.
Author Archives: Ames Herbert
Corn earworm survey and predictions
Annually, we conduct a survey to estimate corn earworm infestation levels in field corn in late July. Earworms develop in corn, then move to other crops such as soybean, cotton, and peanut in August. We determined the number of corn earworms found in 50 ears of corn from 5 randomly selected corn fields in each of 24 counties, totaling 5,800 ears and 116 fields sampled. Statewide, 42% of ears were infested with earworms. This is up from 36% in 2009. Regional averages were 12% infested in Northern, 28% in the Northern Neck, 39% in Mid-Eastern, 58% in the Southeast, and 46% on the Eastern Shore. See the attachment with results from each county and many more details. From the survey, it looks like the areas of greatest risk to heavy infestations of earworms are the southeastern ‘cotton/peanut’ counties, and the Eastern Shore. However, as large as this effort is, it is not a complete picture. We always recommend scouting individual fields to determine exactly what is happening in terms of corn earworm as well as other pests and crop problems. We will continue posting moth catch numbers and other information regarding the 2010 insect pest situation.
Additional information: cew-survey-table10-2-docx
Corn earworm pyrethroid resistance update
As of July 29, we have tested a total of 768 corn earworm moths in our pyrethroid AVT (adult vial testing) program. Although the percent survivorship is down somewhat from last week, we are still seeing greater than 20% survive (see the attached line graph). Could this mean that field failures are likely? Possibly, especially if worm populations are large. Our goal is to process as many moths as we can and post these weekly updates. We are also responding to calls from crop consultants, advisors and growers. We have one reported case of a ‘less than acceptable’ level of control in a peanut field. Could some of those surviving worms have been tobacco budworms, which are known to be more difficult to control with pyrethroids? Possibly, but it is almost impossible to distinguish between corn earworm and tobacco budworm without inspecting the moth parts of the worms under magnification in lab. We do know that budworms can be in the mix, up to 30% one year when we did a lot of worm IDs. Bottom line, this is the third consecutive year that local corn earworm populations are demonstrating high levels of pyrethroid resistance. Proceed with caution and consider non-pyrethroids especially in peanut or soybean fields with a lot of worms.
Additional information: cew-avt-jul-29-2010-ppt
New invasive insect pest of soybean
I am paraphrasing an email we received from Jack Bacheler at NC State last week alerting us to a new invasive insect pest of soybeans. The Figure images (Fig. 1, Fig. 2, and Fig. 3) are attached:
The bean plataspid, Megacopta cribraria Fabricius, is a new invasive pest from south Asia that is currently spreading throughout the southeastern United States (Fig. 1). This insect is a piercing sucking pest (similar feeding as stink bugs) on legumes and was first found on kudzu in Georgia during December 2009. It has since been confirmed on both soybeans and kudzu in both Georgia and SoI am paraphrasing an email we received from Jack Bacheler last week alerting us to a new invasive insect pest of soybeans. The Figure images (Fig. 1, Fig. 2, and Fig. 3) are attached: uth Carolina in 2010. The confirmed distribution is represented in Fig. 2.
Research on insecticide management options is being conducted by Dr. Phillip Roberts, University of Georgia, and his colleagues. The University of Georgia researchers and Dr. Jeremy Greene, Clemson University, are monitoring this pest and we need to be vigilant for the appearance of this pest in North Carolina. Many invasive insects are found in extremely high numbers upon initial establishment, which may aid in our detection of this pest (Fig. 3). Current numbers from Georgia in soybeans are reported as close to 10 insects per sweep near field borders, where the distribution of this pest is the highest.
Please contact me if you see this insect in your soybean field (Ames Herbert, 757-657-6450, ext 411, Herbert@vt.edu).
Additional information: bean-plataspid-jul-22-2010-ppt
Corn earworms are increasing and many appear resistant to pyrethroids
Corn earworm is on the rise. Trap catches started increasing this week, up from near zero last week, and we are seeing moths flying in soybean, peanut and cotton fields. The worst news on corn earworm relates to the resistance monitoring program. As in the past several years, we are testing live-caught male moths in what we call the AVT program (adult vial test). Live moths are placed individually into small glass vials pretreated with a known amount of cypermethrin (the pyrethroid used throughout the south in the AVT program). We check the vials in 24 hours and any live moths are considered to be ‘survivors’ demonstrating resistance. Although we have only tested 363 moths to date, we found that 48% survived in this week’s sample (see the attached chart). This is the highest level ever recorded in Virginia. Last year we found about 40% survivorship in some later season samples, which was the highest level for the years up to 2009. We will continue posting the AVT results, but all indications are that we may be in for some pyrethroid control issues again this summer. Additional information: cew-avt-jul-22-2010-ppt
Cotton insect update: stink bugs low, bollworm increasing
So far we are not seeing much boll damage from stinkbugs. We think this is due to the overall very hot, dry weather we are experiencing. Week before last I saw 106 degrees on a local bank billboard in my hometown (Franklin, VA), the first time ever according to the ‘old-timers’. This week Johnny Parker with Commonwealth Gin reported that he looked at a couple of thousand acres and found only about 3 bolls total with stink bug damage. He says he has never seen stink bug pressure this low. Yesterday he found a hot spot in an irrigated field approaching 10% boll damage with about 15% dirty blooms. The only insect in the field was tarnished plant bug so he assumed they had caused the boll damage (spots with light internal damage).
Corn earworm/bollworm is on the rise. Trap catches started increasing this week, up from near zero last week, and we are seeing moths flying in soybean, peanut and cotton fields. Stan Winslow with Tidewater Agronomic, Inc. in North Carolina reported today that they were finding an increasing number of bollworm eggs in cotton. We are recommending that growers not react to eggs, but wait to see how they progress and base any sprays on worm escapes. If worm pressure gets high, we can expect some escapes. For example, last year we found 2-4% boll damage on some Bollgard 2 and Widestrike varieties. But time will tell. We may or may not have to treat depending on how many worms break through the Bt and Widestrike toxins.
Cotton insect pest update
Not much is happening in cotton right now in terms of insect pests. The hot, dry weather seems to have things on hold, for the most part. Spider mites are common on a lot of field edges but are not widespread. We are not seeing much evidence of square loss to plant bugs (in untreated fields) and square retention is in the 90% + range. A few stink bugs, mostly brown stink bugs, are beginning to show up and soon we will begin assessing bolls for stink bug damage using our newly released ‘Decision aid for stink bug thresholds in Southeast cotton’ which presents a dynamic internal stink bug damage percentage threshold (changes as the crop matures) that begins with 50% internal damage in the first week of bloom. We will post more details soon.
Corn earworm update
It is too early to say a lot about corn earworm, but year in and year out, this critter causes us a lot of problems. Each year we conduct a large survey of field corn in late July to get a ‘read’ on the size of the population that could move to soybean, cotton, peanut and other host crops. Although we have not done the survey, some random checks of sweet corn and field corn show from 40% to 90% infested ears. This constitutes a possible threat. Earworms are worse in dry years as fewer are killed by rain (can drown pupae before they mature, can wash eggs from plants, can increase the incidence on fungal worm diseases, etc.). The other ‘shoe to drop’ is the issue with pyrethroid resistance. In the last two years (2008 and 2009) we found a large increase in the number of moths that survived in our pyrethroid vial testing program (from less than 5-10% survivors prior to 2008, to 20-40% survivors in 2008 and 2009). So far this year we have tested a total of 235 moths from May 27 to the present. The % survivorship has fluctuated, as is normal, starting at 13%, then to 12%, to 7%, to 25% in last week’s sample. Granted these results are from a small number of moths, but all indications are that we may need to address use of pyrethroids again this summer. We will keep posting the information.
General crop insect pest overview
Because of this continuing hot, dry weather, we are not seeing a lot of insect activity in cotton, peanuts or soybeans. There are a few exceptions. Grasshoppers are doing some damage to soybeans in certain areas. Spider mites are starting to show up in most crops, but so far, the buildup is pretty gradual. Finally, there is some hope this Saturday for some decent amounts of rainfall for a lot of the area. If we miss that opportunity&& Potato leafhoppers are showing up in peanuts, but again, the buildup is gradual. We are just beginning to get a picture of how the 2010 corn earworm population is developing. We may be in for some problems (see the Corn earworm update), again, if the weather doesn’t turn around with more frequent rains. PS, if we could shoot about ½ million deer we would solve a lot of our ‘pest’ problems, at least for many of our soybean growers.
Grasshoppers in soybean
Grasshoppers are always worse in dry years. They tend to move from border vegetation or infield weed sources as they dry down (which occurs more readily in dry weather), or from cover crop after herbicide burn down. They will undergo several generations—we find hoppers in all sizes (nymphs and adults) almost any time during the season, especially as we move into late summer/fall. They will eat soybean leaves, but are also capable of feeding on young pods later in the year. Treatment this time of year has to be based on the extent of defoliation. Under normal growing conditions, soybeans are capable of withstanding a lot of defoliation (30-40%) in the vegetative growth stages because they are growing so rapidly constantly putting on new canopy. Of course under these dry conditions, they are standing still, almost. You have to gauge the need for treatment on this tough decision point and it is often a seat-of-the-pants call, as many of them are. If the defoliation is severe and hoppers are abundant, I think you need to consider a treatment. Treating field edges can be effective, especially if hoppers are still moving in from bordering weed sources. If we do not get rain enough to make a decent crop, control efforts and the $ spent will have been wasted—a hard call to make If treatments are made, our limited experience showed that products containing chlorpyrifos (Lorsban 4E at ½ to 1 pt/acre, or Cobalt at 7 to 13 oz/acre) were more effective than pyrethroids. All things considered, I would use the lowest labeled rate. Also, Lorsban 4E is pretty good for controlling twospotted spider mite, which may also be present, or at least a pending threat.