Friday, July 30, 2010

Virginia: Corn Ears Infested With Bollworms - Indicator Of Spraying Trends In Cotton - Hit 42%

Annually, we conduct a survey to estimate Helicoverpa zea (bollworm/corn earworm) infestation levels in field corn in late July.

Corn is considered a nursery crop for 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 nearly a 1:1 relationship between the infestation level in corn and the amount of soybean acreage that gets treated with insecticide for this pest. This means that if 50% of corn ears are infested, we can expect about 49.9% of Virginia’s soybean acreage to be treated for earworm.

 To conduct the survey this year, the number of corn earworms found in 50 ears of corn was recorded in 5 randomly selected corn fields in each of 24 counties, totaling 5,800 ears and 116 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 earworms, or if they had already exited the ears, was also recorded.

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 at the end of this report. We also would like to thank the many growers who graciously allowed us to inspect their fields for earworm.

CLICK HERE for a breakdown of the surveyresults..

  • 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.
  • 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. In a lot of this year’s samples, earworms had already exited from the ears to pupate, which indicates that the process may be a little ahead of schedule.
  • Moths have already begun to emerge from corn fields and the main flight has begun (see our weekly black light trap catches for more details). We are currently conducting an earworm trial in a heavily infested soybean field in Jackson, North Carolina.
  • We will continue posting moth catch numbers and other information regarding the 2010 insect pest situation.

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