Caterpillars (larvae) of the corn earworm, also called the bollworm or podworm, may cause occasional but serious damage to soybean by feeding on flowers and pods. Some leaf feeding may also be observed but is rarely a concern. Large caterpillars may be green, brown or yellow, with light and dark stripes running the length of the body, and they also have sparse setae (hairs) on their bodies. Larvae reach a length of 1.5 inches and have four pairs of prolegs and a pale brown or orange head.
Treatment for corn earworm is most likely when plants are blooming and through the early pod development period (R5). Treatment is generally not recommended prior to flowering. The suggested treatment threshold, based on sweep-net sampling, is shown in the table below. To determine the treatment level, estimate the potential value of the crop and the cost of the insecticide application. For example – if the crop value is $8/bushel and the cost of control is $14/acre, including application costs, the sweep-net threshold would be an average of 8.6 larvae per 25 sweeps.
- Alternatively, treatment should be considered if an average of 1 or more larvae is found per foot of row.
Management options
| Insecticide (Trade Names) for CORN EARWORM | Lb Active Ingredient per Acre | Amount Formulation per Acre | Performance Rating |
|---|---|---|---|
| bifenthrin (Brigade 2E, Discipline 2E, Fanfare 2E) * | 0.063 - 0.10 | 4 - 6.4 oz | 6 |
| chlorantraniliprole (Vantacor 5 SC) | 0.047 - 0.067 | 1.2 - 1.71 oz | 9 |
| chlorantraniliprole, bifenthrin (Elevest) | See label | 4.8 - 9.6 oz | 9 |
| chlorantraniliprole, λ-cyhalothrin (Besiege) | See label | 6 - 8 oz | 9 |
| esfenvalerate (Asana XL 0.66E) * | 0.03 - 0.05 | 5.8 - 9.6 oz | 6 |
| indoxacarb (Steward 1.25) | 0.055 - 0.11 | 5.6 - 11.3 oz | 8 |
| methomyl (Lannate LV 2.4) | 0.23 - 0.45 | 12 - 24 oz | 7 |
| NPV virus (Heligen) ** | ---- | 1.0 - 1.6 oz | 6 |
| permethrin (Pounce 3.2E) * | 0.1 - 0.2 | 4 - 8 oz | 5 |
| spinetoram (Radiant SC 1) | 0.031 | 4 oz | 8 |
| spinetoram, methoxyfenozide (Intrepid Edge) | See label | 4 - 6.4 oz | 8 |
| spinosad (Blackhawk 36% WDG) | 0.038 - 0.05 | 1.7 - 2.2 oz | 8 |
| β-cyfluthrin (Baythroid XL 1) * | 0.0125 - 0.022 | 1.6 - 2.8 oz | 6 |
| γ-cyhalothrin (Declare 1.25) * | 0.0098 - 0.0125 | 1 - 1.28 oz | 6 |
| λ-cyhalothrin (Warrior II 2.08) * | 0.015 - 0.025 | 0.96 - 1.6 oz | 6 |
| Z-cypermethrin (Mustang Maxx 0.8E) * | 0.0175 - 0.025 | 2.8 - 4 oz | 6 |
* Corn earworm has developed some level of resistance to pyrethroid insecticides. Thus, they may not provide adequate control. Use another insecticide or tank mix acephate (at least 0.5 lb active ingredient) with a pyrethroid insecticide if infestations are well above the threshold level.
** NPV virus (Heligen) will only control corn earworm. Applications should be made when larvae are small. Do not apply if most larvae are large or if infestations are well above treatment threshold.
- Infestations are far more likely in late maturing soybean. Planting early and planting early-maturing varieties can help avoid infestations that typically occur beginning in August.
- Moths prefer to lay eggs in open canopies, so infestations are often worse in fields with a wide row spacing or when plant populations are low.
- Avoid unnecessary applications of insecticides that may disrupt populations of beneficial insects.