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Field and Forage Crops |
Bollworm Moth Flights
Although still about a week behind schedule and lower than last year's bollworm moth flights, egg levels in a number of cotton fields north though Wayne and Craven counties have now reached or exceeded the 10 percent terminal threshold. One county Extension agent in Wayne County reported several cotton fields in the 100+ terminal egg range, while other reports from areas south of Wayne County cited egg levels from the 70 range to almost zero. A few agricultural consultants are also reporting some instances of finding more eggs down in the plant canopy on lower squares, stems and blooms than in the terminals, although most egg thresholds are presently being met in the terminals. Remember that when the flight has arrived in the area, low thresholds of 2 percent eggs on fruit or 3 percent small bollworms also triggers insecticide treatment.
Light traps are present in widely scattered areas, and individual farms may have egg and caterpillar levels seemingly at odds with the light trap numbers reported. Bollworm moth numbers can vary considerably between county areas, or even farms or individual cotton fields. In some cases, tobacco budworms may become established just prior to the arrival of the bollworm moth flight. The increases in bollworm moth numbers most appropriately should signal the onset of twice per week scouting (or scouting once per week and conducting twice weekly field assessments in selected cotton fields).
Moth emergence appeared to be starting in Rocky Mount and Tarboro on July 25 with a few very fresh moths in cotton, though very limited egg laying. This was aligned with the three Edgecombe County light traps, which saw modest jumps to the 20 to 50 moths per two nights range this morning. It would appear that the moth flight might be into our northern counties by middle or late next week.
Online Bollworm Moth Updates
One easy method to access current bollworm moth counts (and sometime counts for other species) is to track these flights on the Internet at: http://ipm.ncsu.edu/cotton/insectcorner/blacklight/index.html.
Bollworm Pressure
With our extended corn planting and various ear silking initiation dates, it would appear that our bollworm moth emergence and oviposition could be over a longer period of time than is normally the case. So far, with trap and moth levels lower than in 2002, treatment initiation may be a little less straightforward. Nevertheless, the economic returns of treating at the egg threshold level are almost always positive.
Although plant bugs are at low levels in some fields, in general this pest will likely remain at considerably higher levels than has been the case for several years, especially in our typically less treated Bollgard cotton. A combination of tracking dirty blooms, small damaged bolls (see below), blackened small squares, and observations of adult and nymphal plant bugs in blooms and in terminals should serve as a treatment guide (http://ipm.ncsu.edu/cotton/insectcorner/text.html#pb).
One aspect of the plant bug and the primary method of stink bug damage assessments is the inspection of small to quarter-sized bolls. Quarter-sized bolls typically are the choice for bug damage assessments, although early in the flowering period very small bolls are the only bolls present, and may at times be damaged by plant bugs. One consultant in Halifax County found just over 20 percent internally-damaged small bolls in a cotton field on July 25, with other evidence of plant bug nymphs in white blooms and dirty blooms. My concern is that a number of overlooked cotton fields may fit this category. Be sure to take the potential for plant bug damage seriously this year. For three to four weeks into the bloom period, a threshold of 10 percent internally-damaged bolls (count internal discoloration and/or warts, but not external damage spots) is recommended. Thereafter, the threshold may be increased according to the levels of 3 to 3.5-week-old bug-safe bolls.
Now that the our late season insect pressure has started and more complex insect management decisions are being made on a regular basis, producers and others are encouraged to monitor our twice-weekly cotton insect updates via the Cotton Insect Teletip line (800-662-7301) or on the following Internet site: http://ipm.ncsu.edu/cotton/insectcorner/radio/radio.htm.
As of the July 24 update, the bollworm moth flight is alive, well, and increasing in our most southern counties (that is, Scotland, Robeson, and probably Hoke counties) and is probably just getting into our next tier of counties. The bollworm moth flight is approximately 1 week later than last year's flight. Please consider keeping track of the flights online at our Cotton Insect Corner web page.
When scouting for bollworm eggs, remember to check squares, blooms, and stems in addition to terminals, particularly if the weather turns dry and the cotton becomes stressed. On Bollgard cotton, be sure not to overlook bollworm caterpillars that have a much easier time becoming established under dried blooms than elsewhere on the plant. At the same time, be careful not to over sample these fruit.
The egg threshold remains our best bet for getting a clean start, and a close initial spray interval and/or higher pyrethroid insecticide rates can also be helpful. As mentioned previously, be careful that budworms do not sneak into the early part of the bollworm moth flight. So be aware that a 3 percent budworm threshold on fruit is occasionally reached before the 10 percent terminal or the 2 percent fruit threshold for eggs. Also, do not use an egg threshold for Bollgard cotton unless egg levels reach the 75 to 100+ level in terminals or 8 to 10 on fruit. Other caterpillars, such as loopers and beet and fall armyworms would not be expected this early, although European corn borers could be showing up on cotton in higher numbers than in several years.
On July 22 and 23, a number of reports of cotton aphid fungus presence throughout the middle and southeastern sections of the state were received, and some confirmations of the fungus in several of our northeastern counties. Because the fungus has now apparently become widespread, producers and scouts are urged to check for the fungus before treating for aphids. A 5x to 20x hand lens sometimes makes the identification of this fungus much easier if the fungus is just getting started.
I expect to have much more information on the bollworm moth flight by next week, and within a week or two some information about stink bugs.
Potato leafhoppers are quite abundant this year. The threshold is somewhere in the neighborhood of when 25 to 30 percent of the leaflets show the V- shaped yellowing on the leaf tips. Insecticides can be tank mixed with fungicides. Applications of rootworm insecticides will control leafhoppers.
I saw many southern corn rootworm beetles in peanut fields this past week. So far the summer has been a good one for encouraging rootworm egg survival. This does not mean rootworms will be in a lot of fields, it simply means the risks is a little higher this year. If you are planning to treat for rootworms this year, then I would encourage you to treat by August 5. Treatments after that date may be too late to provide adequate protection.
Corn earworms are coming to a peanut field near you. I fully expect to see corn earworms begin to show up in the next couple of weeks. Watch for the occurrence of this pest, and once again you might be able to tank mix your insecticide with a leafspot fungicide application.
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Last modified on July 28, 2003 by Stephen J. Toth, Jr.