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Cutworm Invasion Risks Rising

Cutworm Invasion Risks Rising

Scout for cutworm and armyworm treatment thresholds; spray quickly.

This week, corn agronomists and entomologists across the Corn Belt raised a caution flag that substantial numbers of black cutworm moths were showing up in traps from Iowa east to Pennsylvania. They're anticipating higher counts over the few weeks due to incoming moth flights.

"Growers should be aware of the increased possibility for upcoming black cutworm infestations, especially in no-till fields with annual weeds," cautions Bruce Battles, Syngenta's agronomy marketing manager. "Unfortunately, weather patterns across the Corn Belt this winter and spring have created field conditions in which black cutworm populations tend to proliferate."

Infestations, according to Syngenta agronomists, can lead to stand reductions of more than 70% in some sections spots. They recommend scouting by checking 20 plants in five locations on every 25 to 30 acres.

If the total of damaged plants exceeds 2% and larvae are smaller than three-fourths of an inch in length, consider treating with an insecticide. As larvae and corn increase in size, the threshold can be raised to 5%. But if the current stand is less than 15% below optimum, maintain the 2% threshold.

The earliest Pennsylvania threat seems to be in the eastern part of the state, says Penn State Extension Entomologist John Tooker. Moth flights are the early-warn signal of potentially heavy egg-laying and cutworm larvae damage later in the season.

On Tuesday, Tooker reported on Penn State's Black Cutworm Monitoring Network that three significant flights of black cutworm moths had been detected in Berks County near Kutztown, Fulton County near McConnellsburg, and in northwestern Lehigh County. Growing degree-day accumulations for the Berks County site were at 210 for Berks County, 145 for Fulton County and 70 for Lehigh County..

Black cutworm cutting behavior can be expected at 300 growing degree days, he adds. With this week's nice weather forecast, at least Berks County would rapidly approach 300 degree days.

Cutworm damage tends to be sporadic. But losses, particularly in corn and wheat, can be severe if egg-laying infests fields at the right time. Watch fields planted adjacent to wheat or into a rye cover crop or fields infested with chickweed. Both are preferred egg laying sites. 

Timing of egg laying and corn emergence is critical. Much of this spring's corn is being planted in weedy fields. That corn will be relatively small or just emerging in late May when cutworm larvae become active.

Risk of damage by true armyworms may also be higher in the next two weeks, suggests Tooker. It's most likely where crops are planted into rye cover crops.

Corn is especially at risk from true armyworms when planted into rye cover crops. Armyworm is of most concern on wheat when feeding on the flag leaf.

Because larvae of both pests could potentially become concerns over the next month or two, growers should remain vigilant for them. Tooker adds that well-timed scouting and spot rescue treatments are usually the most economical tactic for managing both insects.

For more cutworm management details, click on Penn State's black cutworm. Click on armyworm fact sheet for more scouting and control details.

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