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Field and Forage Crops |
Cotton growth is phenomenal in many areas of the state, although a significant part of our cotton production area is in need of rain.
Several different cotton insect pests are present at very high levels in some areas. Stink bugs, although not damaging to cotton until blooming and boll set begins, are presently at higher levels than I think I have seen in my 30 years at North Carolina State University. Additionally, our typical migration of adult stink bugs from assorted hosts into cotton is really just getting started. It is hard to tell for sure what these very high levels portend for our early July through August period of high boll damage susceptibility. It would be reasonable to expect a rough stink bug year on Bollgard and Bollgard II cotton. Additionally, as the county agent and a consultant in Wayne County pointed out earlier this week, even on conventional cotton our high stink bug levels, coupled with early blooming, could translate into boll damage before the onset of the major bollworm moth flight and subsequent insecticide treatments this year. For producers and scouts who have not done so in the past, this year it will be imperative to slice open or squash-open small bolls initially (then switching to examinations of quarter-sized bolls for the remainder of the season when available) for examinations of internal bug damage, beginning with the onset of significant blooming. Check the Cotton Information booklet, the Cotton Insect Scouting Guide, or the Cotton Insect Corner web site for scouting procedures and thresholds.
It appears that plant bugs may add to the problem with stink bugs. Plant bugs also seem to be present at moderate to high levels in many areas this year. In addition to destroying small squares, plant bugs also cause the same damage to bolls as stink bugs. Therefore, scouting for this bug complex (stink bugs and plant bugs) is done simultaneously. Plant bugs have the additional habit of feeding on large squares just prior to bloom. The plant bug-damaged squares open up as dirty blooms, typically an indication of recent plant bug feeding. If dirty blooms constitute 15 percent of the total white blooms in a field, a foliar insecticide spray for plant bugs may be indicated. Visual observations (or sweeping or using a drop cloth) of live adult and immature plant bugs may help to confirm that internal boll damage is recent. As the proportion of the immature nymphs increases, this may be an indication of a reproductively successful, more potentially damaging population of plant bugs.
In pre-blooming cotton, continue to monitor square retention, followed by sweeping for live bugs if retention of small squares falls below about 80 percent.
As if high stink bug and plant bug levels were not enough, cotton aphids are present at moderate levels in many areas of the state. Spraying for cotton aphids is usually not needed if either aphid mummies or the fungus is present, or if moisture is good. But the combination of drought-stressed cotton, observable aphid meltdowns and honey dew on most plants, and the absence of the mummies or fungus, spraying may be needed. If treatment is indicated, use one of the chloronicotinoid insecticides, such as Centric, Trimax or Assail.
Spider mites also seem to be on the increase, with scattered cotton fields beginning to lose bottom leaves and approaching threshold and a few cotton fields treated for mites this past week. Although the parasitic fungus that can wipe out spider mites on cotton is similar to the aphid fungus and can often be triggered by rain, it is not as dependable. At a minimum, significant rainfall will certainly allow the plant to withstand mite feeding. Mite damage starts out as a light stippling on the leaves, followed by some leaves turning red to bronze, and finally with the lower leaves turning yellow and falling from the plant. If the presence of spider mites in a cotton field is hard to determine, then you probably do not have an economic problem and a hand lens directed at the base of the mid-vein on the underside of the several cotton leaves can help confirm the presence of the small active mites and their eggs.
It would appear that our major bollworm moth flight might be early this year. However, as of the June 25 we should be a good two and a half weeks from the beginning of the flight in southernmost North Carolina.
A cotton scouting school has been scheduled for Wilson and Nash counties at 4:00 p.m. on July 15 at the Wilson County Extension Building on 1806 SW Goldsboro St. in Wilson. Contact Norman Harrell (telephone: 252-237-0111; e-mail: norman_harrell@ncsu.edu) or Charlie Tyson (telephone: 252-459-9810; e-mail: charlie_tyson@ncsu.edu) for details.
In many areas, adequate soil moisture has contributed to good growth of peanut plants and early season thrips damage is starting to disappear. There are some signs of leafhopper feeding. If you plan to apply insecticide for rootworms, this application will also control the leafhoppers. The symptoms of tomato spotted wilt virus are now starting to show. As the weather becomes hot, the plants will be stressed and many more plants with symptoms will begin to appear. This does not mean that the virus is being spread by thrips, but rather it was infected early and the signs are just starting to show. DO NOT apply additional insecticide for thrips control if you start to see a lot of virus. You will be wasting money. If you plan to treat for rootworms but have not, now is the time to get that treatment in the field.
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 June 28, 2004 by Stephen J. Toth, Jr.
