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Manhattan KS 66506-4004

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Sorghum Insects

Cutworms (various species)

Cutworm damage to sorghum is infrequent, but growers should be alert when early season cutworm damage has occurred in neighboring cornfields. Damage is likely in the two weeks after planting, so fields should be scouted during and shortly after emergence.

Rescue treatments should be considered if a majority of larvae are less than ½-inch long. Worms of this size can destroy four to six additional plants each before completing development. Older larvae are harder to kill and less is gained by controlling them because they have already caused most of their damage.

Consider the amount of stand reduction that can be tolerated before deciding to treat. If the minimum stand density recommended for a particular hybrid under your management program is 40,000 plants per acre and you have 50,000, then you can tolerate a stand reduction of 20 percent before treatment becomes economically justified, assuming the losses will be even across the field. If cutworm damage is localized in certain areas, spot treatments applied to affected areas will be more cost-effective than treating the whole field.

Other factors that affect the decision to treat include the length of the areas where seed failed to grow in a row and the planting date of the sorghum. Gaps less than 2 feet long may be partially compensated by plant tillering, but longer areas are of more concern. Sorghum planted earlier than mid-June tillers more than sorghum planted later, making later plantings less able to compensate for cutworm stand reduction.

Please refer to the most recent version of the Sorghum Insect Management Guide for specific control recommendations.

Page last updated on 10/31/2013 by J.P. Michaud.