 |
Field and Forage Crops |
Bugs, namely stink bugs and plant bugs, have been present in cotton at higher levels than in recent memory. Square retention counts remain the best indicator of possible plant bug problems until about a week after blooming begins. Even though it is tempting to put in a plant bug or stink bug material with Pix or other similar growth regulators, I recommend that growers confirm both less than 80 percent square retention and the presence of threshold levels of live plant bug in sweep nets before adding an insecticide.
If treatment is needed for plant bugs, growers must decide between one of the new chloronicotinoid insecticides like Centric, or one of the older organophosphate insecticides like Orthene, Vydate, Bidrin or others. Centric and Trimax, though more expensive, are kind to beneficial insects and will control cotton aphids. On the other hand, organophosphate insecticides are less costly and control more stink bugs but they also eliminate beneficial insects, sometimes flaring cotton aphids and greatly increasing bollworm survival if the major moth flight is less than about 10 days away or is ongoing. Pyrethroid insecticides are another option, both inexpensive and effective against plant bugs and green stink bugs, but they also sometimes flare cotton aphids and leaving about half of the brown stink bugs behind.
Unlike most other years, high populations of stink bugs in many areas of the state could damage developing bolls before the arrival of the major mid to late July moth flight.
Within no more than about a week after initial blooms have been noted a cotton field, samples of small bolls should be sliced or crushed open to find internal boll wall warts or stained lint. Once quarter-sized bolls are available, stick with this size for further sampling. Later in the season, as the proportion of stink bug safe 3.5-week old bolls increases, stink bug thresholds may be adjusted upwards.
If threshold levels of 10 percent boll damage are present in the first 30 days of blooming and green stink bugs predominate, one of the pyrethroid insecticides is recommended. If brown stick bugs predominate, then Bidrin or a high rate of Orthene is suggested. As with plant bugs, be aware that applications of organophosphate insecticides may increase the survival of other insects such as cotton aphids and bollworms. Expect stink bug levels to vary both within and between cotton fields. These spotty distributions make widespread blanket applications questionable. Inspections of the contents and inner surfaces of boll walls are the key in determining the possible need to treat for stink bugs and will remain so for the next 6 to 8 weeks.
Although cotton aphids are also plentiful in many areas of the state, spraying for aphids in cotton is usually not needed if moisture levels are good. If drier conditions return, more situations requiring insecticide treatment will probably arise, but so will be likelihood of the fungus or aphid mummies arriving to save the day.
From July 2, the major bollworm moth flight should start in approximately 10 days to two weeks, beginning in the southern part of the state.
Diamond 0.83EC insecticide was recently registered by the U. S. Environmental Protection Agency. It is marketed by Crompton/Uniroyal for use in cotton for control of plant bugs, stink bugs, budworms/bollworms, beet and fall armyworms, and suppression of thrips and whiteflies. I do not have experience with this product. It is an insect growth regulator and works against immature stages of insects by interfering with the molting process, and it kills immature insects slowly. It is not active against adult insects. It may have some fit for us as a plant bug material. Data show relatively long residual activity, longer than Bidrin but about the same as Centric. As a stand-alone it is used at 9 to 12 ounces per acre for plant bugs and as a tank mix (e.g., with an adulticide), 6 to 9 ounces per acre is suggested. Although Diamond is labeled for bollworm control, I suspect that it would be inferior to the pyrethroid insecticides as a stand-alone product, and I also doubt that it would add little as a tank mix partner for a pyrethroid insecticide. I am unaware of it's activity against tobacco budworms.
On June 29, I received telephone calls concerning aphid infestations in cotton in Martin, Bertie, Tyrrell, Chowan, and Beaufort counties. Practically all cotton fields have at least a background aphid infestation at this time. Those fields with high populations usually had Orthene sprayed on them earlier, especially if Thimet or Disyston was used as the at-planting thrips insecticide. In Beaufort County, there have been reports of aphid fungus showing, but the other sites mentioned little evidence of biocontrol. What can growers do? The threshold for aphids is given as a rating scale and is available on page 140 in 2004 Cotton Information. If aphid levels are above threshold or near threshold with little biocontrol, spraying is in order. The best treatment is Centric 40WDG at 1.25 to 2.0 ounces per acre. Trimax 4F at 1 to 1.5 ounces per acre is a second choice, but it has not been as good as Centric in replicated trials. Higher rates should be used on more intensive aphid infestations or on larger plants.
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 6, 2004 by Stephen J. Toth, Jr.