Corn earworm moth catches were low this week, with nightly means ranging from zero to two moths. Brown marmorated stink bug captures were low in all locations except Petersburg (with approximately 20 per night). Please click on the link below that says “BLT_7_31” to see the Tables for detailed captures of these two pests. Thanks to the following for their reports this week: Mary Beahm, Chris Drake, Scott Reiter, Keith Balderson, Mark Kraemer, Janet Spencer, and Ames Herbert and his entomology team.
Category Archives: Pest Group
Results of the Corn Earworm Survey in Virginia Field Corn—2014
Annually, we conduct a survey to estimate Helicoverpa zea (corn earworm) infestation levels in field corn in mid- to late July. Corn is considered a nursery crop for corn earworm, allowing the pest to complete a lifecycle and then move on to other crops such as soybean, cotton, and peanut in August. Over 30 years of data show that there is a linear correlation between the infestation level in corn and the amount of soybean acreage that gets treated with insecticide for this pest.
To conduct the survey this year, the number of corn earworms found in 50 ears of corn was recorded in 5 corn fields in each of 29 counties, totaling 7,250 ears and 145 fields sampled. When fields were known to contain Bt or non-Bt corn, this was noted. Otherwise, samples were considered to be random and assumed to be representative of the actual Bt/non-Bt composition in each county. Age of corn earworms, or if they had already exited the ears, was also recorded (data not shown). We greatly appreciate the help of Virginia Cooperative Extension Agriculture and Natural Resource (ANR) Agents, Virginia Tech faculty and staff, and volunteers in this effort. These cooperators are acknowledged in the attached Figure. We also would like to thank the many growers who graciously allowed us to inspect their fields for corn earworm.
Results of the survey are provided below (click on the Figure to enlarge it). Statewide, approximately 20% of ears were infested with corn earworm. For comparison, 18% of ears were infested in 2013, 30% in 2012, 33% in 2011; 40% in 2010; and 36% in 2009. Regional averages for 2014 were 6% infested ears in Northern counties, 4% in the Northern Neck, 18% in Mid-Eastern, 17% in South-Central, 30% in the Southeast, and 17% on the Eastern Shore.
This survey is intended to be a representative sample, 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. Also, please check the black light trap reports on the Virginia Ag Pest and Crop Advisory and other reports posted weekly to keep up-to-date on the insect pest situation.
Brown marmorated stink bug update for soybeans
As of this week, brown marmorated stink bug adults, nymphs, and egg masses are beginning to show in a few soybean fields in seven counties (Madison, Warren, Campbell, Appomattox, Prince Edward, Amelia and Nottoway). Number are still very low but more are expected as they move from border trees into fields. This early movement is coinciding with the maturity of the soybean crop. Most of the plants in the infested fields are in late R3-early R4 growth stages. When plants reach the R5 stage (seed fill), they will become even more attractive to stink bugs that target young seed to feed on.
Kudzu bug update for soybeans
The number of counties where kudzu bugs have been found in soybean fields has increased a lot since last week. Last week they were found in 4 counties and this week a total of 18 counties. In many cases both nymphs and adults are present. To my knowledge, none have reached the threshold for this second generation, that is, 1 nymph per sweep. Keep in mind that as much time as we put into this statewide survey of soybean fields, our scouts can only visit a small fraction of the fields. Our recommendation is that you check all of your fields. The best way is to use a standard sweep net doing several 15 sweep samples in a field. If you need a sweep net, here is one recommendation (there are several other sources): Bioquip, the sweep net with the 2 ft long handle, item #7625HS (https://www.bioquip.com/search/DispProduct.asp?pid=7625HS). Note that the site lists two handle lengths, again, we recommend the one with the 2 ft long handle.
Corn earworm update—slow to develop but some surviving the pyrethroid vial test
The corn earworm population is very slow to develop this year. We are only getting a couple of moths each night in our black light trap here at TAREC and our pheromone trap catches are way down compared to this time last year.
Sean Malone will be posting the results of our annual corn earworm field corn survey later this week. Those results, the percent of ears damaged by corn earworm, give us the best indication of what to expect in the coming weeks. Worms feed in corn, drop the ground to pupate in soil chambers, then adults (moths) emerge to fly to other hosts like soybean, cotton and peanut fields. So the size of the population in field corn is our first indicator of what the season may bring.
As in past years, we are also subjecting moths to the AVT (Adult Vial Test) with a pyrethroid insecticide. With the low population, mentioned above, we have not tested a lot of moths but the survivorship numbers are high 13-46 percent. I cannot forecast if this will increase as the season progresses, as it has in the past, but starting at this level is significant. Given these early results, regardless of the crop growers should be prepared to use some non-pyrethroid product ‘designed’ to target difficult to control corn earworms. These can be used alone, or tankmixed with a pyrethroid if other pests like stink bugs or kudzu bugs need to be controlled.
Soybean kudzu bug update—July 24, 2014
Our scouts have reported finding kudzu bugs in soybean fields in 4 counties. Nymphs as well as adults were found in two of those counties, Lunenburg and Prince William. Adults and nymphs were found in kudzu, only, in two other counties. All are near the southern border of the state. We are expecting this to change pretty rapidly so we strongly recommend that you start checking fields. This is most easily done with a sweep net. Go to several areas of a field, especially along the edges, and do several 15 sweep samples. At this point in the season, treatment thresholds should be based on the 1 nymph/sweep threshold.
Cotton stink bug update—July 24, 2014
We are finding (and hearing about) a few cotton fields that have reached or exceeded stink bug damage thresholds—not all by any means, but some. For the most part, these are fields in the 3rd or 4th weeks of bloom. If you are following our recommended cotton stink bug thresholds, the threshold for the 3rd, 4th and 5th weeks of bloom is 10 percent internal stink bug damage. The research that these thresholds are based on showed that these weeks are the most critical for boll production and the bolls present during this period are the most susceptible to stink bug feeding injury.
If you have not started checking fields for stink bug damage to bolls, you might want to consider starting. In each field, pull a random sample of at least 25 bolls that fit in the ‘holes’ in our scouting card (contact us or your local extension office if you need a stink bug scouting card). Using bolls in this size range guarantees that you are sampling the right boll population. Crack each boll and inspect for internal stink bug feeding injury symptoms.
What products will give you the best control of stink bugs and longest residual activity? Our field trials, and others, show pretty consistently that pyrethroids and products like Bidrin provide the best control. Insecticides in the neonicotinoid class, if applied alone, are weak. Although products do a decent job of killing the adults and nymphs, none provide much residual activity —even 7 days would be a stretch. If adult stink bugs continue move in to field, more than one application may be needed.
Black light trap catches for the week ending July 24, 2014
Nightly average catches of corn earworm moths in local black light traps were: Charles City=18.5; New Kent=8.0; Warsaw=1.0; Essex=zero; Petersburg=1.1; Eastern Shore AREC/Painter=zero; Hampton Roads AREC/Virginia Beach=zero; Southampton=3.0; Sussex = 1.9; Suffolk=2.5.
Means per night for brown marmorated stink bug were: Charles City=1.3; New Kent=zero; Warsaw=0.7; Essex=zero; Petersburg=26.9; Eastern Shore AREC/Painter=zero; Hampton Roads AREC/Virginia Beach=zero; Southampton=zero; Suffolk=zero. Thank you to our trap operators for their reports this week: John Allison, Mary Beahm, Keith Balderson, Mark Kraemer, Helene Doughty, Chris Drake, Kelvin Wells, and Ames Herbert and his entomology crew.
Late blight found on Tomato in Leesburg, VA
Unfortunately, late blight has been confirmed in Leesburg, VA by the Plant Disease Clinic in Blacksburg. Potato and tomato growers (especially in the northern part of the Commonwealth) should take precautionary actions and increase scouting. For more information on late blight please refer to the extension publication link about this potentially devastating disease. Please let us know if you have any more questions.
http://pubs.ext.vt.edu/ANR/ANR-6/ANR-6_pdf.pdf
Southern Rust on Corn in North Carolina – Update
Southern rust was confirmed on a sample from Camden County, NC on July 21. At this time, southern rust has NOT been reported in Virginia. Yield of corn at or near the dent stage is unlikely to be impacted by the disease, but less mature corn may need to be protected with a fungicide application. Contact your local extension office for recommendations if you suspect southern rust is in your area. Samples of corn plants with symptoms of southern rust should be submitted to your local extension office or the disease clinic at the Virginia Tech Tidewater AREC (contact Dr. Hillary Mehl, hlmehl@vt.edu). Typically the disease has little impact on Virginia corn since it arrives too late in the season to affect yield, but if southern rust is confirmed in Virginia prior to corn reaching the dent stage (R5), fungicide applications may be warranted. Updates will be provided as more information is obtained.