Outbreaks often follow a midsummer drought, which causes the corn to ripen earlier and become less attractive to the moths. Female moths prefer to lay eggs in open-canopied, late-blooming soybean fields. Drought conditions also delay soybean maturity and prevent normal canopy growth, so peak moth activity is more coincidental with blooming of open-canopied fields.
Sampling should start during mid-August and be repeated at least weekly in each field until a spray decision is made or the pods are no longer available due to advanced maturity. Concentrate first on the high-risk fields that are late blooming, open canopied, or previously treated with insecticides. The best way to sample is by placing a standard 3-foot drop cloth between rows and shaking vigorously the row sections of plants over the cloth. Each shake sample consists of a total of 6 feet of row and at least 10 samples should be taken in every 40 acres. The number and size of earworms should be recorded along with observations on the presence of natural enemies.
In narrow-row or broadcast beans, a drop cloth is impractical and, thus, a 15-inch sweep net must be used. Walk along the rows, swinging the sweep net so that the opening passes through the foliage. The net is turned 180 degrees after each sweep as you advance with each step to swing the net through the foliage in the opposite direction. Each stroke is counted as one sweep. A series of 25 sweeps should be taken at each of 10 sites in every 40 acres.
Treatment is suggested if drop cloth counts exceed one medium to large earworm per narrow foot row of beans or two per wide foot row of beans (greater than 20 inches). If using the sweep net method and counts exceed three medium to large earworms per 25 sweeps in narrow foot row of beans or broadcast beans or five per 25 sweeps in wide foot rows, treatment is necessary.
The timing strategy is to wait until most of the larvae are 0.375 inch or more in length, and then treat when pod damage is first evident. This allows for most egg laying and hatching to occur before treatment and, thus, reduces the chances of a second spray being needed later. Some defoliation may occur before it is time to treat, and this injury should be evaluated just like that of any defoliator. If other defoliating pests are present when pod damage is first evident, then adjustments should be made in the treatment thresholds for earworms. For example, if green cloverworms are actively feeding and have already caused 15 percent defoliation, then insecticide treatment would be justified at lower earworm infestations, about one-half the normal threshold. Finally, treatment may not be necessary if the majority of worms are infected with the fungus disease. This white to greenish-white fungus can have a significant impact on earworm populations.
Increasing levels of podworm resistance in the South is evidence that pyrethroid insecticide is gradually losing effectiveness. In 2004 for the first time, Virginia reported control failures of pyrethroids in soybeans at rates that should have killed most larvae. To avoid future resistance, many states now recommend nonpyrethroids such as Larvin, Lannate, Penncap-M, and Steward.
You are viewing records 1 - 5 of 15. Next 5 Records| Insecticide and formulation | Rate of active ingredient per acre | Rate of formulation per acre | Time lmits: Days before harvest | Remarks |
|---|---|---|---|---|
| esfenvalerate (Asana XL 0.66EC) |
0.03-0.05 lb | 5.8-9.6 oz | 21 | Restricted Use: Corn Earworm Only. |
| indoxacarb (Steward EC) |
0.055-0.11 lb | 5.6-11.3 oz | 21 | Particularly effective on beet armyworm and other podworms that have developed resistance to pyrethroids. Use the 7.2-oz rate for best control of mixed-size beet armyworms. |
| lambdacyhalothrin (Lambda-Cy 1EC) |
0.025-0.03 lb | 3.2-3.84 oz | 30 | Restricted Use: Use high rates for fall armyworm; not effective on beet armyworm |
| lambdacyhalothrin (Warrior II) |
0.025-0.03 lb | 1.60-1.92 oz | 30 | Restricted Use: Use high rates for fall armyworm; not effective on beet armyworm |
| methomyl (Lannate 2.4LV) |
0.23-0.45 lb | 0.75-1.5 pt | 14 | Restricted Use: |
