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Edited by Tom Kuhar, Assistant Professor, Dept. of Entomology, Virginia Tech
Greetings crop producers, researchers, extension personnel, and crop consultants,
Weather summary for week ending May 7, 2004, Painter, VA
James T. Custis (Farm Manager, ESAREC)
Threat of rain all weekend with only 0.02" Saturday pm then rain most of the day on Monday and for a total of 0.52". Some other parts of the Shore may have gotten more! Maximum air temperature of 76 F and a minimum of 44 F and soil temperature 68 F for a high and a low of 58 F for 2" and 4" soil depth. The rain slowed field work for a day or so, but it was needed and it is drying out very fast. It looks we may need some more rain by the first of the week.
Blacklight and Pheromone Insect Traps
Jack Speese & Tom Kuhar (ESAREC)
Blacklight trap (BLT) in Painter, VA: For about a month, we have been battling a very persistent bird that insists on making her nest in our blacklight trap. Consequently, insect catch data has not been very accurate to date. 0 cutworm moths, 1 European corn borer moth, 1 green stink bug
BLT in Cheriton, VA: 174 ECB moths, 2 black cutworms, 1 spotted cutworm, 1 corn earworm
In summary, the first generation European corn borer moth flight is upon us on the lower Eastern Shore.
Northampton County news from our roving reporter in the field
(Bill Shockley (VCE, Northampton Co.)
There has been a marked increase in European corn borer moth activity at blacklight traps in Cheriton. We're seeing a lot of cereal leaf beetle activity in small grains. Scouting should begin for thrips activity in newly emerged string beans. We have received approval for the use of Reflex for string bean application, more information will follow.
Insects in rye windbreaks in tomato fields
Tom Kuhar & Jack Speese (ESAREC)
We are currently investigating the importance of rye windbreaks as reservoirs for insect pests.
In early May of last year and late April to May of this year, we conducted a study in commercial tomato fields on the Eastern Shore of Virginia to determine: a) which insect pest species were found in the rye windbreak strips, and b) if it is necessary to spray the rye strips with insecticides along with the tomato spray-applications. Although growers would save money by not spraying the rye strips, it is equally important to avoid the buildup of large populations of pest species. Species of particular concern are the thrips that vector tomato spotted wilt virus (TSWV). In Virginia, the tobacco thrips, Frankliniella fusca, is the most common vector of the disease.
Results showed that most of the insects that were found in the rye strips were associated with small grains such as English grain aphid and cereal leaf beetle, and were of no consequence to adjacent tomatoes. However, two potential tomato pests, tobacco thrips and eastern flower thrips, were found in the rye strips, but both species were found in relatively low numbers.
Additional research has shown that in relatively short (immature) rye (10-14 inches tall), a high mortality of insects occurred in the rye strips after tomato rows were sprayed with insecticides (pyrethroids or SpinTor). This occurred even when the spray nozzles directed over the rye strips were turned off and only the tomatoes were sprayed. In a dense, tall stand of rye (>15 inches tall), the insecticide drift mist from the tomatoes was not sufficient to kill insects in the rye.
Potato Disease Control
Christine Waldenmaier (ESAREC)
Late Blight - We have accumulated 14 disease severity values (DSV) in lower Northampton County and 13 DSV in upper Accomack County since April 15th. The first fungicide spray according to the Blitecast computer model should go on after the accumulation of 18 DSV. These may accumulate within the next week; however, with little rainfall it may be longer than a week before we reach the threshold. At this time the threat of late blight is not very high, however, if you need to fertilize your potatoes this week, you may want to consider applying a protectant fungicide such as mancozeb, polyram or chlorothalonil.
Colorado potato beetles are active
Tom Kuhar (ESAREC)
This week we saw our first Colorado potato beetles moving on to potato plants at the research station. Most potato growers in Virginia applied a neonicotinoid insecticide at planting, such as Platinum, Admire, or Tops MZ Gaucho. All of these products are still very efficacious to CPB based on our insecticide efficacy trials and surveys of treated potato fields on the Shore. Moreover, based on resistance monitoring of CPB beetles collected from Cape Charles last year, we have very little tolerance to imidacloprid (the active ingredient in Admire, Gaucho, and Provado) building up in our beetles relative to other areas, such as in NJ and Long Island. In fact, we had some of the most imidacloprid-susceptible beetles around, surprisingly. We will be carefully monitoring this situation. Beetles will be collected and assayed from farms in Horntown, VA and Cape Charles this year.
Cereal Leaf Beetle Update
Ames Herbert (Virginia Tech Tidewater AREC)
Just when you think you have it figured out, things change. A sage entomologist once advised me that predicting insect activity was a risky business that "they'll make a liar out of you every time." I made some comments in my last advisory on cereal leaf beetle that have not played out and it is due to the shift in weather. I predicted that due to the (at that time) unseasonably warm weather that CLB populations would move through quickly. The onset of this late spring cool/wet weather has slowed things down. Remember that rates of insect development are driven by temperature, with each species having its optimal developmental range. CLB thrives best under the current conditions, when temperatures are in the 50° -70° F range. The onset of hot weather will drive them into their summer dormancy stage.
This means of course that the infestations are going to linger and continue to cause problems in grain fields. Our best advice is to continue scouting fields to find the ones that reach economic threshold. As we know, many grain fields have already been treated with insecticides so scouting could be restricted to only previously untreated fields.
How long do fields need to be scouted and protected with insecticides? Our previous research showed that grain yield is most affected by leaf defoliation during the boot stage through grain fill stages, buts remains sensitive up to the dough stage. After that, leaf loss is inconsequential. Especially high yield potential fields should be protected through the dough stage. Our work also showed that single insecticide treatments provided season long protection provided they were not applied too early, not before beginning stem emergence (Zadoks stage 31, Feekes stage 6). Also, there are differences in products and rates, especially if applications are made early which requires the best residual activity.
Finally, there has been a lot of feedback about my last CLB note regarding Warrior T versus Mustang Max for CLB control in wheat. My comments were based on my 2002 field plot research in wheat, and these data have been "out there" for public scrutiny for almost two years. I can send you a copy of the report for details. To summarize, two field trials were conducted. In trial one, applications were made when the CLB population was in the egg/small larval stage, which is the stage that our economic threshold hold is based on. In trial 2, applications were made when the CLB population was older, all medium and large-sized larvae and no eggs, when many growers actually make applications. In these trials, differences in the numbers of larvae found on separate post treatment sampling dates were relatively subtle among the different pyrethroids and rates tested. However, there were important differences in the cumulative data, expressed as cumulative larval days (CLD). The CLD is a value that represents the total number of larvae in a treatment, over all replicates, for the entire post treatment sampling period (the equation for calculating the CLD is in foot notes of the tables in the attached report). In trial one, the CLD represents a 28-day post treatment period, and in trial two, a 19-day post treatment period. Treatments with the fewest larvae over the entire post treatment period have the lowest CLD value.
In trial one, where treatments were applied early to egg/small larval populations and more residual activity was needed to last the entire 28-day post treatment period, Warrior T treatments resulted in the lowest CLD values and it took the higher rate of Mustang Max (4.0 oz/acre) to achieve a similar value. In trial two, where treatments were applied later and less residual activity was needed since the CLB population was older (larvae only, no eggs), there was little difference in the CLD among the two products and rates tested.
These data DO NOT imply that Mustang Max is not effective in controlling CLB in wheat. They do indicate that higher rates may be needed if long term efficacy is required.
Thomas P. Kuhar
Assistant Professor
Department of Entomology
Eastern Shore Agricultural Research & Extension Center
Virginia Polytechnic Institute & State University
33446 Research Drive
Painter, VA 23420
E-mail: tkuhar@vt.edu
Tel: 757-414-0724
FAX: 757-414-0730
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