Damage caused by fall armyworms and corn earworms may occur from July through frost. The armyworm may attack the whorl, causing a ragged, shot-hole appearance to the leaves, but applications of insecticides in the whorl stage are generally unprofitable. Both species of caterpillar feed in the heads of sorghum during the bloom period through the milk stages. Open-headed hybrids are damaged less than the compact-head types. The small, fuzzy, striped sorghum webworms also feed within the developing seed. This problem is usually more severe in the late-maturing fields from mid-August to October.
These pests can be found in the whorl during June through July. Although the ragged “shot hole” damage may be dramatic, control of worms in the whorl stage seldom is economically justified. One exception is the European corn borer, which can be a potentially major pest problem on sorghum in the mid-Atlantic area. Whorl infestations are similar to those in corn; however, the tunneling injury has a much greater impact on sorghum yield because of the smaller stems and damaged grain heads that drop off later. Insecticide treatments are suggested if 50 to 80 percent of the plants are infested with live larvae.
Begin sampling blooming-stage fields in early August by counting the number of worms of each species on a minimum of 200 random plants from 20 different areas in fields 10 acres in size or less. Make frequent head inspections when sorghum is beginning to flower, and continue at 5-day intervals until hard dough stage. To examine heads for sorghum webworm, beat heads on a piece of white paper or cloth. Small larvae (less than one-eighth of an inch in length), which are commonly overlooked during head inspections, will be detected with this method.
Control to prevent yield losses from whorl damage should be considered if 40 to 60 percent or more of the plants are infested and show heavy leaf damage. For head infestations, treat only when larvae are damaging the head or when the developing growing point and the number of fall armyworms and corn earworms averages more than two per head. For webworms, treatment is suggested where infestations average five or more worms per head during the postbloom period.
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 |
|---|---|---|---|---|
| carbaryl (Sevin 80S) |
1.5 lb | 3.0 pt | 21 | Webworm control only. A ground application with at least 15 gallons of diluted spray is preferred. Aerial applications should use 5 gallons of spray per acre. No preharvest waiting period is required for forage use. |
| carbaryl (Sevin XLR 4F) |
1.5 lb | 3.0 pt | 21 | Webworm control only. A ground application with at least 15 gallons of diluted spray is preferred. Aerial applications should use 5 gallons of spray per acre. No preharvest waiting period is required for forage use. |
| chlorpyrifos (Lorsban 4E) |
0.5-1.0 lb | 1.0-2.0 pt | 30 (1 pt rate) 60 (2 pt rate) | Restricted Use: Webworm control only. Do not apply more than 1.5 pounds active ingredient per acre per season. Do not treat sweet varieties of sorghum. |
| lambdacyhalothrin (Warrior) |
0.02-0.03 lb | 2.56-3.84 fl oz | 30 | Restricted Use: Use for earworm and fall armyworm control of first and second instars only. Do not graze livestock or harvest for silage or hay. |
| methomyl (Lannate LV 2.4EC) |
0.45 lb | 1.5 pt | 14 | Restricted Use: Methomyl is preferred for fall armyworm and all other species control both in whorl and head. Use high gallonage and direct spray into whorl for best results. |
