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Field and Forage Crops |
Plant bugs continue to be present at higher levels in cotton fields than in a number of years, with scattered fields throughout the state being treated –- more so in the far eastern counties. Although not as dramatic in sheer numbers, or as obvious in plant symptoms as cotton aphids, plant bugs can sneak into cotton fields and cause considerable headaches for producers unfamiliar with their damage potential.
From the beginning of squaring until approximately a week into the bloom period, square retention counts are the most sensible way to find out if plant bugs may be a potential problem. A square set of about 80 percent or more healthy small terminal and lateral squares signals at least a temporary all clear for plant bugs. Unfortunately, adults can rapidly invade cotton fields from surrounding drying down or senescing vegetation, so square set should be assessed weekly on all fields, with twice weekly checks on a subset of these fields.
Low square retention triggers sweep net sampling at this time of year, and along with live bug observations and the presence of blackened squares, helps determine if plant bug levels may be high enough to warrant treatment. For now, a high percentage should be adults in most cotton fields. A sweep threshold of about 8 plant bugs per 100 sweeps is recommended. Because adult plant bugs may change their location within the plant canopy, the field itself and even in and out of cotton fields, sweep net and other kinds of sampling for these mobile insects can be less reliable than sampling for stationary or slow insects like eggs and caterpillars. However, following recommended scouting procedures greatly increases the odds of providing good enough plant bug assessments or fruit damage levels to make correct management decisions most of the time. Lack of diligent scouting for plants bugs this year could be costly in some areas. As is sometimes experienced in several of our far eastern counties, plant bugs could remain a problem well into our boll production period, especially on Bollgard cotton.
Because plant bugs have not developed resistance to insecticides in the Carolinas and Virginia (that we know of), a number of chemical options exist if thresholds are reached (see the 2003 North Carolina Agricultural Chemicals Manual). If aphids are present along with plants bugs and the aphid parasitic fungus is not present, organophosphate insecticides such as Orthene and Bidrin, while active against plant bugs and cost-effective, may increase aphid levels. Centric and Trimax at the high-recommended rate (0.05 pound of active ingredient per acre) should provide good to acceptable control of both pests, with pyrethroid insecticides being the appropriate choice for bollworm/plant bug combinations once the major flight gets underway.
We will have more information on plant bugs and the refocusing of scouting efforts on internally damaged small bolls and dirty blooms next week.
Cotton aphids continue to be found at treatable levels in some cotton fields, though less so in our southern-most counties due to outbreaks of the fungus, Neozygites fresenii. In a survey of of aphids in 16 cotton fields conducted on July 16 in Scotland County, 15 of 16 fields had both cotton aphids and the fungus present. Once the fungus is noted in a cotton field, insecticide treatment should not be needed. Hopefully, this coming week, the fungus will be making a significant dent in aphid levels in many of our counties. However, treatable aphids populations can be expected in some fields.
Based on the progress of the bollworm moth flight in South Carolina, we can expect the moth catches to pick up the Rowland area next week, probably putting the flight about a week behind last year. However, given the late maturity of much of our cotton crop and the unknown size of the upcoming flights, this could still become a challenging bollworm year for conventional cotton. By next week's issue of the North Carolina Pest News, more specific information will be available on these flights. To keep up with the status of these flights on line, the counts (many of these counts are updated the day the traps are checked) are provided on the Internet at the following location: http://ipm.ncsu.edu/cotton/insectcorner/blacklight/index.html.
All of the rainfall and high humidity was probably helpful for European corn borer establishment on silking corn. When this larval generation develops, cotton will be one of the oviposition targets of the subsequent moths. Sweet corn also appears to be infested at pretty high levels this year, as well as early weeds hosts such as cocklebur. In North Carolina, the European corn borer has not been much of an economic problem on bolls for about the last 6 or 7 years. With more conventional cotton planted this year than last and the probability of higher upcoming European corn borer moth flights, it will be interesting to see how things shape up, particularly if the rainy weather patterns continue.
In most cotton fields, the onset of the bollworm moth flight and the subsequent oviposition on cotton triggers the beginning of pyrethroid insecticide applications on conventional cotton. However, producers and scouts should be reminded that it is not unusual for a somewhat earlier budworm moth flight to precede the major bollworm flight. Budworms are hard to kill with pyrethroids, the mainstay of bollworm control. So, in addition to keeping up with the bollworm moth flights, scouts should be alert to the possibility of the 3 percent larval threshold sometimes being reached by budworms before the bollworm egg or larval thresholds. The best early indicator of the possibility of these budworms is seeing the striped budworm moths in cotton fields or in surrounding vegetation, by using budworm pheromone traps, or by use of a bollworm/budworm Hel-ID Kits (manufactured by Agdia; http://www.agdia.com/helid/).
On June 30, EPA completed a thorough assessment of the pesticide carbaryl, one of the most widely-used insecticides in agriculture. Stemming from the Agency's evaluation, EPA is requiring new measures to ensure protection for homeowners, agricultural workers and the environment. EPA's actions will reduce potential exposures of residential users and children to this pesticide by eliminating most pet care and aerosol products, as well as liquid lawn care applications. Exposures to people who apply carbaryl in agriculture and those who enter treated areas will be reduced in the following ways: canceling some uses and application methods; reducing maximum application rates; eliminating aerial application for certain crops; requiring more personal protective equipment and engineering controls; and extending restricted entry intervals for many crops. Carbaryl can pose risks to honey bees, aquatic invertebrates and other aquatic animals. No concerns were identified related to dietary exposure to residues of carbaryl. EPA will also conduct a cumulative risk assessment for carbamate pesticides, and when this is completed, the Agency will evaluate whether further risk mitigation may be needed for carbaryl. A Federal Register notice announcing the beginning of a public comment period on the decisions contained in this action will be published shortly. The Interim Re-registration Eligibility Decision for carbaryl, and related documents including EPA risk assessments and a summary of this decision, will be available on the Internet at: http://www.epa.gov/pesticides/reregistration/carbaryl/ .
Source: EPA Pesticide Program Update, U. S. Environmental Protection Agency's Office of Pesticide Programs, July 8, 2003
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 21, 2003 by Stephen J. Toth, Jr.