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Field and Forage Crops |
With about a week left in August, we are beginning to see our late season mix of various caterpillars and bugs, with potential insect damage from this point in time influenced both by pest levels in a local area and by the attractiveness and susceptibility of cotton plants. Some cotton is now cutting out to the point of being essentially immune to most insects, while significant acreage is still late with an attractive lineup of new squares, blooms and bolls of various sizes. On late cotton, insects such as bollworms, plant bugs, stink bugs, European corn borers and fall armyworms could still present a problem in some fields for the next few weeks.
The next bollworm moth flight started in the southern counties a couple of days to about a week ago, as seen by light trap counts in those counties and reports by scouts and consultants. I was in Onslow County on the morning of August 22 and saw very high levels of bollworm moths in our test plots. Our earlier, rather extended major bollworm moth flight has also resulted in pockets of moths in localized areas throughout the state. These and soon to emerge moths can still result in significant damage to bolls on late-maturing plants if they become established on immature fruit and move down the plants to larger bolls.
Fall armyworms have increased in many areas of the state, varying from low, non-treatable levels to fruit establishment in the 2 to 6 percent range (or more in a few cases). Unfortunately, all of the familiar cotton insecticides, as well as the new insecticides such as Intrepid, Denim, Confirm, Tracer and Steward, provide poor control of medium and large fall armyworms. Therefore, fall armyworms need to be either kept from becoming established in the first place via a pyrethroid insecticide applied primarily for bollworms, or by a pyrethroid plus a material that has activity against small stages of fall armyworms. The pyrethroids Karate and Capture have shown good activity in the past in keeping fall armyworms from becoming established, while a 1/4 to 4/10 pound active ingredient rate of Larvin, Lorsban or Curacron plus a pyrethroid as a tank mix seems to control most small fall armyworms in squares, blooms and feeding between the bracts and outer surface of bolls or various sizes. Similarly, a pyrethroid plus one of the newer materials (mentioned above) as a tank mix should also control small fall armyworms. Remember that Bollgard cotton is generally resistant to European corn borers, but is susceptible to fall armyworms.
On the positive side, in North Carolina fall armyworms have traditionally had a difficult time becoming established after September 1. After than time, even small fall armyworms feeding between inner bract surface and the outer boll surface of medium and small bolls seem to die out. Hopefully, this year will be the same.
Stink bug damage to small and medium bolls appears to be increasing in some cotton fields. Assessments of internal damage to thumb-sized bolls and adjusting thresholds upwards (probably 20 to 40 percent damage to quarter-sized bolls by now in many fields) to account for the presence of larger stink bug-safe bolls are recommended.
Hopefully, good boll loads in many areas of the state will push cotton towards a timely cutout within the next two to three weeks.
Caterpillars, primarily corn earworms, continue to occur in the peanut crop. They are found in all sizes, so the infestation will be around for a while. The treatment threshold is 4 earworms per row foot this time of year, but increases to 6 to 8 earworms per row foot the first of September. Since most of the crop is fairly lush, I would not pull the trigger too quickly on these infestations.
Potato leafhoppers continue to cause yellowing in peanuts. A few days of sunny, warm weather often sets leafhopper populations back, but those days have been few and far between for most areas this summer. The combination of leafhoppers and corn earworms makes the decision to apply recommended insecticide in the spray tank with your leafspot spray a little easier.
Spider mites seem out of the question now, but don't completely forget about them as I have seen problems occur in September with significant leaf loss.
Dow AgroSciences recently received a label for the use of Tracer (spinosad) on peanuts for insect pests such as corn earworm, beet armyworm, and fall armyworm. The use rate is from 1.5 to 3 fluid ounces per acre for corn earworm to 2 to 3 fluid ounces for armyworms. The higher rates are for larger worms and more severe infestations. There is a 3-day preharvest restriction and several hay and forage restrictions. A maximum of 9 fluid ounces per acre (or three applications) can be applied with intervals as short as 7 days.
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 August 25, 2003 by Stephen J. Toth, Jr.