Black Cutworms, Armyworms Concerns For Growers

Jill Scheidt, agronomy specialist with University of Missouri Extension in Barton County, scouted area fields to prepare this week’s field scouting report.

Scheidt says armyworms are still being seen at threshold level in wheat and fescue fields.

Threshold level for armyworms in wheat and fescue are 4/ sq. ft. or when 2%-3% of heads are clipped. Mustang Max is recommended to control armyworm because it provides the longest residual effect.

“Armyworms were moving slow, but keep a close eye on them, checking 2-3 times per week for threshold levels, as armyworms at threshold levels can clip heads on half a field in one night. Recent rains may have slowed feeding and may have brought in a fungus that kills armyworms.

Below threshold levels of 1%-2% of corn plants were clipped above ground due to black cutworm feeding. Threshold levels for black cutworm are when 6%-8% of plants are clipped above ground or when 2%-3% of plants are clipped below ground.

“Scout fields for black cutworm until corn reaches the 5-leaf stage. Black cutworms do not feed on corn once it is past the 5-leaf stage,” said Scheidt.

“If you are thinking about switching from corn to soybeans, soybeans should NOT be planted into fields where applications of atrazine or an atrazine premix have already been made this season,” said Scheidt. “The label says soybeans should not be planted until the following year due to the likelihood of soybean injury from residues of atrazine that may still be present in the soil.”

The average field half-life of atrazine is 60 days. High soil pH’s (>7.5) will also slow the degradation of atrazine, along with cool soil conditions. Fortunately, replanting corn or planting grain sorghum into these damaged areas will still be an option.

The weekly field scouting report is sponsored by University of Missouri Extension and Barton County Extension.

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