The corn earworm moth flight is underway, but is still pretty light compared to past years. Worm numbers are gradually increasing in soybean, peanut, cotton, and sorghum fields, but are still not at economic levels.

Worms are rarely, if ever, an economic threat to peanuts as they feed only on leaves, feed for only a short time, and do not remove enough leaf area to result in any yield loss. So why do most peanut farmers spray their fields for worms when there is no chance that those sprays will improve the yields?

We are finding a few worms in soybean fields, but not many. And, if fields are not in the R5 growth stage (seed forming in the pods), worms are not a threat. They are only a threat when they start eating seed, so if no seed are present, there is no need to treat. If seed are present, a good rule-of-thumb threshold would be to treat if you catch an average of 1 to two per 15 sweeps—but only if seeds are present.

Most cotton, unless very late planted, is mature enough to be safe from worms. At this point in the season, it would be very hard to justify treating most cotton fields for worms.

Sorghum is a different story. Corn earworms are highly attracted to sorghum heads, especially late planted sorghum. For more information on this, read to sorghum insect pest advisory that was just posted.

We are detecting a pretty high level of pyrethroid resistance in the corn earworm moths we are testing. The attached figures show this. With 705 moths tested so far this year, we are seeing an increase in the number surviving with a cumulative average of 37.5 percent survival. From the attached figure, you can see that this is high compared to previous years. Non-pyrethroid insecticides will need to be considered, especially if heavy infestations occur.

Corn earworm moth captures started increasing in area black light traps, ranging from 0.3 to 7.5 per night.  Brown marmorated stink bug nightly averages ranged from zero to 12.9.  Please see the data tables for specifics.  Thanks to the following for their reports this week:  John Allison, Scott Reiter, David Moore, Mary Beahm, Austin Brown, Janet Spencer, Keith Balderson, and Ames Herbert and his entomology crew. BLT_Aug_6

To date, we have tested 371 H. zea in adult vial tests, with a mean survival rate of 31.9% in the treated vials (5 micrograms cypermethrin).  Please see the attached Figure for more details:  AVT_6_Aug

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 earworm larvae found in 50 ears of corn was recorded in 5 corn fields in each of 25 counties, totaling 6,250 ears and 125 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, summer agricultural assistants, and interns 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 larvae.

Results of the survey are provided in the Figure (CEW_survey_2015). Statewide, approximately 17.5% of ears were infested with corn earworm. This is even lower than the numbers reported in 2014 (20%) and 2013 (18%)—both years with very few cotton, peanut or soybean fields being infested with treatable numbers of worms. Regional averages for 2015 were 4% infested ears in the Northern Neck, 13.4% in Mid-Eastern, 9.5% in South-Central, and 27.7% in the Southeast.

So far, all indicators point to another year with few fields reaching thresholds. We will continue monitoring and posting updates.

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.

Corn earworm moth captures ranged from zero to 2.3 per night in area black light traps; brown marmorated stink bug nightly averages ranged from zero to 1.3.  Please see the attached data tables for more details.  Thanks to the following for their reports this week:  Mary Beahm, Keith Balderson, David Moore, Scott Reiter, Austin Brown, Mike Parrish, and Ames Herbert’s entomology crew.  Special thanks to those hosting the black light trap locations!  BLT_30_Jul_2015