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Watch for this wheat bug

Jeff Caldwell 01/03/2013 @ 10:25am Multimedia Editor for Agriculture.com and Successful Farming magazine.

One bug might be pouring salt on the wounds from a dry, harsh winter for the winter wheat crop in the Plains.

Though it's not the most common insect pest in the crop world, the winter grain mite can have major implications for the future of an already stressed Plains winter wheat crop as it stretches its legs to come out of dormancy soon.

Reports started surfacing from the field in late December of winter grain mites in areas like south-central Kansas, causing Kansas State University Extension wheat agronomist Jim Shroyer to encourage farmers to keep their eyes peeled for the bug in their own fields, especially considering this winter's specific weather conditions.

"With the fall we had, and as warm as it was late into the year, there were more chances for those insects to hang around and do more damage later in the year," Shroyer says. "We'll know more when the wheat starts to green up in late February and March."

The warmer temperatures that stretched later into the fall in places like southern Kansas allowed for the bugs to lay eggs later toward winter. But this particular bug is unique in that it thrives under cooler conditions, says University of Delaware Extension integrated pest management (IPM) specialist Joanne Whalen. The two conditions combined to create an environment conducive to the mite's reproduction.

"Egg laying is heaviest between 50 and 60 degrees Fahrenheit and the optimum conditions for hatching are between 44 and 55 degrees," Whalen says. "Mite activity in the spring drops rapidly, and the eggs fail to hatch when the daily temperature exceeds 75 degrees."

Winter grain mite damage -- which is more common in fields under duress from adverse conditions like nutrient deficiencies or drought stress -- can come in two forms: Reduced winter forage stands and standability, and lowered grain yield potential after the crop emerges from dormancy. The former is a greater potential issue in this year's Plains hard red winter wheat crop at this point, Shroyer says.

"Any type of damage due to insects like winter grain mite weakens the plant, then it really doesn't take that cold of temperatures to cause some winter damage," he says. "It's kind of a cascade of events: First, you have the insects come in, weaken the plant, then it's more susceptible to cold damage."

Damage can range from plants that appear "grayish or silvery" in color to leaf tips that have a scorched appearance and ultimately, plants that die altogether. Most infected plants, Whalen says, don't die but will see both forage and grain yields go downhill quickly.

If you don't see obvious outward signs like these in your fields, scouting closer may be necessary. In doing so, check both plant residue and the soil's surface for the mites, focusing your scouting to cooler times of day, Whalen says.

"The most effective scouting method is to use a 10x hand lens, checking both plant foliage and crop residue on the soil surface for the presence of immature and adult mites," she says. "A sweep net may also be effective in determining if mites are present. The best time to scout is early in the morning and at dusk on calm days because the mites will seek refuge during the day in the top 4 or 5 inches of the soil profile to avoid the sunlight. On cool, overcast days, they may be observed actively feeding on plant foliage throughout the day."

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