The Black Cutworm Equation: Damage Potential = Weed Growth X Eggs Laid

The combination of early season weed growth and moth activity determine the potential for black cutworm damage to newly set plants. A green flush of low-growing weeds in fields prior to transplant provides attractive sites where cutworm moths can lay eggs. Our cool, wet spring has encouraged early season weed growth in many fields so there have been plenty of places for moths to lay eggs. The numbers of moths flying at night and laying eggs completes the equation for potential damage.

Pheromone Trap Captures

Graphs of black cutworm pheromone trap captures from the University of Kentucky Integrated Pest Management (IPM) program provide pictures of weekly 5-year average (green line) and 2015 (blue line) activity at Princeton and Lexington. Princeton (Figure 1a) had above-average moth captures in early April that have since dropped steadily. This points toward declining populations in fields in western parts of the state, but the cutworms still present should be large. They can inflict significant damage soon after plants are set.

Catches in the Lexington trap (Figure 1b) show above-average moth flight from late April through late May. In this case, smaller black cutworms would be expected in fields and more leaf feeding should be seen before they grow large enough to sever plant stems.

Figure 1a. Weekly black cutworm (BCW) moth capture in Princeton, KY.  The blue line represents the 5-year average; the green line represents counts in 2015.  (UK IPM)

Figure 1a. Weekly black cutworm (BCW) moth capture in Princeton, KY. The blue line represents the 5-year average; the green line represents counts in 2015. (UK IPM)

Figure 1b. Weekly black cutworm (BCW) moth capture in Lexington, KY. The blue line represents the 5-year average; the green line represents counts in 2015.  (UK IPM)

Figure 1b. Weekly black cutworm (BCW) moth capture in Lexington, KY. The blue line represents the 5-year average; the green line represents counts in 2015. (UK IPM)

 

Black Cutworm Activity

Many black cutworms that have been feeding on weeds survive final field preparation. With their food source removed by tillage, they will be ready to feed on whatever plants become available. Cutworms feed at night and hide in the soil during the day. Round notches in sides of leaves or cut stems usually are the most visible signs that cutworms are present.

Scouting for Black Cutworm

Check groups of 20 consecutive plants in several parts of fields, looking for cut or wilted plants. Carefully dig in the soil around the base of a damaged plant to look for the hiding grayish cutworms. They are likely to be near the surface and feeding aboveground if soil moisture is moderate, but they tend to feed and hide deeper if the soil is very dry. This can affect control success because cutworms feeding below ground are less likely to contact or consume an insecticide spray deposit.

Check tobacco fields for signs of cutworm feeding twice a week for the first 2 weeks after transplanting. Watch for leaf-feeding or cut plants. The general treatment guideline is 5% or more injured plants. Infestations may be spotty in a field.

Figure 3. Wireworm larva tunneling within tobacco stem (Photo: Lee Townsend)

Figure 3. Wireworm larva tunneling within tobacco stem (Photo: Lee Townsend)

Note: In some cases, wireworms may be the cause of wilted plants. They will tunnel in the stem rather than chew through it. Unlike cutworms, wireworms will be inside stems (Figure 3), not out in the soil. There is no rescue treatment for wireworms.

Cutworm Management

Any of the following insecticides can be used as a broadcast spray for cutworm control:

Belt, Besiege, Brigade, Brigadier, Capture LFR, Endigo ZC, Orthene 97, Skyraider, or Warrior 1 CS.

 

 

By Lee Townsend, Extension Entomologist

 

 

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