 |
Field and Forage Crops |
Beet armyworms have occurred in a number of cotton fields in at least 15 counties in the past 10 days or so, especially where conditions have been dry. This marks the earliest occurrence of damaging levels of this species in North Carolina since 1977.
Even non-treatable levels of beet armyworms can appear frightening to producers and scouts accustomed to treating for three small bollworms per 100 fruit on conventional cotton in July and August. The biggest challenge for producers and consultants during the coming days and perhaps weeks will be to determine whether treatable levels exist. This is often not a straightforward decision.
The rather protective insecticide treatment level of 5 hits (active, hatching egg masses) per 100 feet does not appear to be well suited to the present situation in pre-blooming cotton. This threshold is a holdover from the days in which information on hit levels were required to obtain a Section 18 Emergency Exemption for a chemical that had not been labeled for beet armyworms on cotton.
Cotton plants can often compensate completely for terminal and square damage in the 50 percent range during the pre-bloom period. Also if the little fuzzy white rice-like Cotesia cocoons are present on cotton leaves, treatment with insecticide may not be needed. The maggot-like immature stage of these parasitic wasps, which feed within the beet armyworms, can greatly reduce levels of these pests.
Insecticide treatments at this time of year are probably better based on terminal and square damage in excess of 50 percent, with an active population of beet armyworms. Cotton can tolerate a significant amount of defoliation (probably 30 percent or more) at this time of year, and even 5 to 10 percent appears to be pretty serious. Newly-hatching beet armyworm egg masses should also be taken into consideration, as they indicate that the infestation will either continue or may be just getting underway. A number of cotton fields have fit into the above treatment category, although thankfully most at this time have not.
Treatment with Tracer, Steward or Intrepid insecticide will be expensive (approximately $7.25 to $17 per acre). Control of beet armyworms with these new compounds should be at least satisfactory, and often excellent. Do not treat beet armyworms with pyrethroid insecticides, as this class of insecticides will kill beneficial insects but not beet armyworms, often significantly worsening the situation. Also resist the temptation to treat at the first sign of beet armyworms.
A return to wetter weather (experienced by many North Carolina counties in the past few days) often greatly reduces the occurrence of these pests. Also, a greater time interval following the last insecticide application for thrips often results in lower beet armyworm establishment. At present, it is anyone's guess as to the intensity or duration of these beet armyworm outbreaks.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on July 1, 2002 by Stephen J. Toth, Jr.