To conserve biological control agents such as parasites and predators, avoid unnecessary spraying. For example, alfalfa weevil parasites and predators, such as big-eyed bugs and lady beetles, and other predacious insects remain in alfalfa fields throughout the season. These same predator species also spread to adjacent corn, soybean, and vegetable crops to search for prey and then return to alfalfa fields in late summer and early fall to feed on aphids, leafhoppers, and late-season caterpillar pests. Alfalfa is considered an excellent "catch crop" for beneficial insects, especially during dry hot weather. The catch crop is an important asset for the entire farm crop system.
Intercrop systems of oats and alfalfa aid in the establishment of spring-seeded alfalfa. By growing quickly, the oat plants reduce weed growth while allowing the slower-growing alfalfa to become established. The oat plants also aid in the drying process, especially in fields with tri-species mixtures of oat, alfalfa, and orchardgrass. Studies have demonstrated that densities of potato leafhopper are significantly reduced when oats are planted with alfalfa.
Begin scouting established alfalfa fields the first week after the first cutting. New field seedings should be sampled beginning in early May. Resample each field once a week. Use a 15-inch sweep net anytime during the day as long as the foliage is dry. Sweeping wet alfalfa is difficult, and the samples are almost impossible to count. Take 10 sweeps at each of 10 random locations in the field. Count the number of adult and nymphal leafhoppers for each set of 10 sweeps. Tally the total, and record the number per 100 sweeps. Examine 20 random stems to determine average stem height and the percentage of plants in the bud or flower stage.
If the leafhopper count per 100 sweeps exceeds 10 times the average stem height, control is recommended. For example, alfalfa 6 inches in height should be treated if counts exceed 60 leafhoppers per 100 sweeps. If alfalfa is more than 60 percent bud or in flower or if more than 28 days have elapsed since last cutting, plan to harvest within 7 to 10 days and avoid spraying. However, resample the field soon after cutting to determine the need for control. Remember that none of the insecticides carries over to the next cutting, so control decisions must be made independently on each cutting. Also note that potato leafhopper sprays will have a minimum impact on the survival of the alfalfa weevil parasites.
Treatments must be applied before yellowing begins. If stunted, yellowed plants appear as a result of leafhopper injury, the field should be harvested immediately rather than sprayed. This profile conserves beneficial organisms.
You are viewing records 1 - 5 of 9. Next 4 Records| Insecticide and formulation | Rate of active ingredient per acre | Rate of formulation per acre | Time lmits: Days before harvest | Remarks |
|---|---|---|---|---|
| chlorpyrifos (Lorsban 4E) |
0.25-0.50 lb | 0.5-1.0 pt | 0.5 pt: 7, 1 pt: 14 | Restricted Use: Some temporary yellowing may occur after application but should disappear within a week and not cause yield loss. |
| beta-cyfluthrin (Baythroid XL) |
0.0065-0.0125 lb | 0.8-1.6 oz | 7 | Restricted Use: |
| dimethoate (Dimethoate 4EC) |
0.25-0.50 lb | 0.5-1.0 pt | 10 | Restricted Use: May be less effective during drought conditions. |
| lambdacyhalothrin (Lambda-Cy 1EC) |
0.015-0.025 lb | 1.9-3.2 oz | 1 for forage, 7 for hay | Restricted Use: |
| lambdacyhalothrin (Warrior II) |
0.015-0.025 lb | 0.96-1.60 oz | 1 for forage, 7 for hay | Restricted Use: |
