Farm Progress

Alfalfa weevil is first pest to look forWait until threshold to treatPea aphids, cutworms also on the watch list

March 8, 2011

1 Min Read

As alfalfa breaks dormancy, producers should keep a close watch for insect activity, said Jeff Whitworth, K-State Research and Extension entomologist.

“Alfalfa weevils are probably the first and foremost insect pest to scouting at this time of year. Scouting for alfalfa weevil should begin as soon as the plants break dormancy,” Whitworth said.

“Some eggs were probably deposited last fall. With the warm weather we have had sporadically and which can be expected over the coming weeks, we have accrued several degree days or thermal units towards hatching these eggs. Heat units accumulate for alfalfa weevils at temperatures above 48 degrees Fahrenheit,” he said.

However, do not be too quick to treat for alfalfa weevil. Wait until the field reaches the treatment threshold.

The next insect to watch for would probably be pea aphids, Whitworth said.

“They can also start relatively early in the spring, and can be a problem on first-year stands. If weevil treatments are applied, the insecticides will wipe out any beneficial insects, which normally do a good job of keeping aphid populations under control,” he explained.

Also, producers should keep an eye out for army cutworms as there were reports of army cutworm activity last fall. Army cutworms will start feeding again anytime temperatures are above 50 degrees Fahrenheit, Whitworth said.

Armyworms are another potential problem.

Those are the early season pests which have the most potential for damaging alfalfa prior to the first cutting, Whitworth said.

More information on control is available at local K-State Research and Extension offices and in K-State publication MF-809, Alfalfa Insect Management 2011, at:

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