Crops are Emerging . . . Must be Cutworm Time!

There have been reports of cutworms in sugar beet from Moorhead, Crookston, Hillsboro and MinnDak. This is the expected timing for Red-Backed and Dark-Sided cutworms in beets; both occur in the Red River Valley and they have similar life cycles.  They both over-winter as eggs laid by the adult moths in cultivated fields at the end of summer. The following late May/early June, the eggs hatch and the caterpillars move onto seedling crops. 

Scouting –  Early detection is important with this insect. Cutworms feed mostly in the evening and at night and so are sometimes difficult to locate in the daytime. Their feeding (Figure 1), usually at or below ground level, causes wilting, death and sugar beet seedlings are often cut off near ground level. Scouting for these worrisome worms is best done by looking for wilting or dying plants and then looking in the top 1”-2” of soil at the base of these plants. 

Thresholds & Treatment – An economic return on treatment can be expected when 4% - 5% of beets seedlings are cut in a field.  Pesticides are best applied in the evening as it results in high levels of insecticide being present during the cutworms’ period of greatest activity. High humidity, dew and light rains (mist) can carry the insecticide over the plant surfaces and into the soil to increase contact with the insect. For the same reason, liquid formulations tend to be more effective against cutworms. To assist in delivering the insecticide to the caterpillars, break up severe soil crusting prior to, or during application. Table 1 lists the insecticides labeled in 2006 for controlling cutworms on sugar beet.

For more information, go to the Red River IPM site at:

http://www.nwes.umn.edu/ent/redent.html

. . . A Little bit More on Cutworms

Several cutworm species affect regional crops (Figure 2). Dingy cutworms, Feltia jaculifera, overwinter as partially grown larvae. They are the first cutworm species to cause problems during crop emergence, anytime from late April to late May. Female moths of the dingy cutworm are known to lay eggs on sunflower heads and other late-summer flowering plants from mid-July through September. Crops following sunflowers in rotation are at greatest risk of injury from this species. Other high risk sites in the fall include freshly cultivated weedy fields or newly seeded winter wheat.

Other cutworms, such as the red-backed, Euxoa ochregaster, and the dark-sided, Euxoa messoria, overwinter as eggs that hatch in mid to late May. Eggs are laid in the fall and survive in weedy, wet and reduced-tillage areas. Feeding injury from these cutworms normally occurs in late May to early June.

The black cutworm, Agrotis ipsilon, and the variegated cutworm, Peridroma saucia, migrate into the region as adults and occasionally cause problems in row crops.

Some criteria that can help predict cutworm problems are:

1. field history of cutworm damage;
2. surface crop residue from reduced or minimum tillage;
3. bottom land or low spots in the field;
4. fair to poor drainage; and
5. proximity to shelterbelts or field margins with grassy ground cover.

Because the most important cutworms lay eggs during late summer in our region, soil moisture at that time is important for their winter survival. Growers should be cautious when planting any crop following pasture, alfalfa or clover. Cutworm survival may be greater in these types of locations.

Ian MacRae, U of MN Extension Entomologist
and
Phillip Glogoza, REE-Crops, Moorhead

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