Cutworms in vegetables

Early season cutworms can attack seedlings by clipping the stems at the soil surface, usually in late April and early May; however, there have been reports of cutworm damage over the past couple weeks (Fig. 1). Damage is likely to occur in areas that had green vegetation early in the spring (weed patches, cover crops) or along the field edges. Many cutworm species attack vegetable crops; however, the black cutworm (Fig. 2) is likely the culprit in brassica crops. In bulb vegetables, the black cutworm and dark-sided cutworm (Fig. 3) are usually a problem.

Figure 1. Cutworm damage
These pests may be a problem this season due to a couple of factors. First, due to the cool, wet conditions we’ve seen so far, weed management may be a challenge. Weed patches are attractive to female cutworms looking to lay eggs. Second, again due to the weather conditions, the push back of planting dates may mean that plants are in the susceptible seedling stage when the cutworm larvae are larger.

For most vegetable crops, when 5% of the plants are damaged, control of cutworm is warranted. In sweet corn, control measures are warranted when 10% of the plants are damaged until the 5th leaf stage, after which they are not usually a pest. Remember that smaller larvae (< 1”) are easier to control than larger ones. Cutworm larvae over an inch in size will also stop feeding in preparation for pupating.  Most cutworm species are active during the evening, so try to apply insecticides during this time. In most crops, some pyrethroids, chlorpyrifos and/or chlorantraniliprole (Coragen) can be used for cutworm control. Please follow the directions for use as per the product label. Refer to Publication 363, Vegetable Crop Recommendations for specific cutworm control options by crop.

Figure 2. Black cutworm larva
Figure 3. Dark-sided cutworm larvae
 

Dig around the plants to find the culprit when deciding on control measures, as white grubs and wireworm may cause similar damage in some crops.  This will also allow you to determine the size of the larvae.

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