Natural enemies usually keep corn leaf aphids under control. If a field is heavily infested but more than 20 percent of the aphids appear brown and swollen from being parasitized or more than one aphid predator per 50 to 100 aphids is present, then insecticide is generally not necessary. The use of resistant hybrids is an important tool in greenbug management. In areas where aphids consistently damage sorghum, growers are encouraged to consult with local seed dealers about the possibility of resistant hybrids. Also keep natural enemies in mind. Greenbugs that are parasitized turn into brown or bronze mummies and cling to the leaves. If a field that has reached the threshold level also has more than 20 percent of the aphids appearing brown and swollen from being parasitized or there is more than one aphid predator per 50 to 100 aphids, control generally should be delayed because predators and parasitic wasps should soon bring the infestation under control.
A minimum of 40 randomly selected plants from different areas of the field should be examined each week. Aphids are seldom evenly distributed across a field. Avoid examining only field borders. Examine a greater number of plants in fields larger than 80 acres. Record the leaf symptoms caused by aphid feeding, and estimate the infestation level of aphids and the presence of natural enemies.
The corn leaf aphid is the predominant aphid found feeding on sorghum in our area. This insect can damage seedling plants; however, larger plants generally tolerate high numbers of aphids without economic loss. Research has shown that yield losses have occurred only when the aphid causes stand loss. On larger plants, infestations of 800 to 1,500 aphids per plant do not substantially reduce yield. In addition, corn leaf aphids are generally controlled by beneficial insects found in grain sorghum. Treatment should only be considered if aphid populations are increasing and seedling plants are dying. Natural enemies usually keep corn leaf aphids under control. If a field is heavily infested but more than 20 percent of the aphids appear brown and swollen from being parasitized or more than one aphid predator per 50 to 100 aphids is present, then insecticide is generally not necessary.
In comparison, the greenbug aphid can cause significant economic loss. If chemical control is considered, refer to the treatment threshold table below and decide on the basis of the number of aphids per plant, leaf damage, percentage of parasitized aphids (mummies), and the ratio of aphid predators to aphids.
You are viewing records 1 - 5 of 5.| Insecticide and formulation | Rate of active ingredient per acre | Rate of formulation per acre | Time lmits: Days before harvest | Remarks |
|---|---|---|---|---|
| chlorpyrifos (Lorsban 4E) |
0.25-1.0 lb | 0.5-2.0 pt | 30 | Restricted Use: Do not apply more than 1.5 pounds active product per acre per season. Do not treat sweet varieties of sorghum. |
| dimethoate (Dimethoate 4E) |
0.25-0.50 lb | 0.5-1 pt | 28 | |
| dimethoate (Dimethoate 2.67E) |
0.22-0.44 lb | 0.75-1.5 pt | 28 | |
| malathion (57% EC) |
0.75 lb | 1.5 pt | 7 | A ground application with at least 15 gallons of water per acre is preferred. Use at least 5 gallons of diluted spray per acre for aerial applications. |
| zeta-cypermethrin (Mustang MAX) |
0.02-0.025 lb | 3.2-4.0 oz | 14-45 | Restricted Use: Not for greenbugs. Pre-harvest intervals are 14 days for grain and stover, or 45 days for forage. Do not make applications closer than 10 days apart. Apply with a minimum spray volume of 2 or 10 gallons per acre by air or ground, respectively. Maximum allowed amount per crop season is 0.125 lb ai per acre. |
