FIELDAND
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The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
Very high populations of beet armyworms have been causing significant damage to cotton in a number of cotton fields in the southern part of the state. Hardest hit at this point is the area of Hoke, Scotland and Robeson counties. Beet armyworms typically become established in dry conditions; however, these populations are occurring under both wet and dry conditions. The threshold used by many entomologists for beet armyworms is 5 hits per 100 feet of row. Some fields were running as high as 60 to 85 hits per 100 feet. A reasonable threshold would be 8 to 10 percent beet armyworms on squares or young bolls, and the presence of 3 egg masses or active hits (hatched out) per 100 feet of row. The majority of cotton fields in these and in other counties are not at treatable levels, but, as of August 14, the infestation is increasing in most areas. Although beet armyworms are at low levels in most counties, their presence is widespread. Treatable levels have been found at the Upper Coastal Plain Research Station this past week, and in all fields in the Goldsboro area two days ago. Beet armyworms are also scattered lightly throughout our upper northeastern counties. These levels do not constitute a problem, but rather the potential for developing into economically-significant infestations. It is difficult to predict what these populations will do at this point. It is probably fair to say that beet armyworms likely exist at some level in all of our cotton-producing counties.
A Section 18 Crisis Exemption for North Carolina use of Pirate was just turned down on August 14 by the Environmental Protection Agency. With various state-approved packages on their desk for the use of this product under Specific Exemptions, this decision seems irrational. Julie Haigler, Pesticide Section, North Carolina Department of Agriculture and Consumer Services, is presently inquiring if the EPA will permit us to submit a package for a Specific Exemption (which requires much more data, and which would normally take weeks to complete) and use the background data from another state. If approved, this could make product available by Wednesday, August 19. Hopefully, we will know more by the weekend. If granted, this exemption will allow up to two applications of Pirate at the 0.2 ounce rate, at a cost of approximately $12.40 per acre. This product should provide good control of high populations of beet armyworms, and excellent control of more moderate levels. Let's hope we get this product in time to do some good.
The last bollworm flight has picked up again throughout most of cotton-producing counties, though at much lower levels than the major July flight. We still have enough moths in many areas to generated localized infestations in cotton which is still squaring and blooming. In fields in which speckled bolls occur all the way to the top, treatment will no longer be needed. In most cases where squares and blooms become difficult to find, economically-significant infestations are unlikely. With fairly mature cotton, which is still susceptible to bollworms (blooms near the tops of plants but several nodes of squares present), thresholds can probably be increased to 6 small bollworms on squares or upper bolls. There is probably no need to treat if scouts find 3 or less large bollworms. If producers have medium to large worms in the 6 percent range, a high pyrethroid rate will likely be needed. In late, or otherwise lush, cotton, particularly in fields with good yield prospects, cotton could well be in need of further protection. Probably best to stick to a more standard threshold of 3 or 4 live bollworms on fruit in this situation. Additionally, European corn borers can be another factor in this later-maturing cotton. Do not use eggs as a trigger to spray. Egg hatch often starts dropping about this time of year for a number of reasons, and after the initial application(s) I do not advise using an egg threshold. Our fast push toward cutout should significantly lessen the need to treat for bollworms.
Fall armyworm reports continue to trickle in. Primarily low to moderate levels along with varying degrees of bollworm infestation; just enough to make treatment needed and chemical selection difficult. Three to four percent each of bollworms and small fall armyworms in cotton which is still susceptible can probably be dispatched with a low pyrethroid rate and 0.3 of Larvin or Lorsban. Karate probably gets the nod for keeping additional fall armyworms from becoming established. Higher levels of small fall armyworms (4 to 6 or 8 percent) and low levels of bollworms should be reasonably well controlled with 0.3 to 0.5 pounds of active ingredient per acre of Larvin or Lorsban. Medium to large fall armyworms can not be effectively controlled with any labeled insecticide. Fall armyworms will have a difficult time becoming established in cutout cotton fields in which the availability of squares and bloom are limited.
Corn earworms are very abundant in some fields and are present in
nearly all fields. Some populations are running as high as 12 to
15 corn earworms per row foot which far exceeds the 4 per row
foot threshold for insecticide treatment. Spider mites are also
being found in scattered areas and in some locations are causing
damage. Before making a decision to treat with miticide, check
the underside of the leaves with a hand lens to see if the mites
are still active. In many locations, even areas that are still
quite dry, a fungal pathogen has killed many of the mites. No
matter how serious the damage, if there are no active mites,
there is no need to treat.
Web page last updated on August 17, 1998 by Stephen J. Toth, Jr..