Brittle snap in corn - also called green snap - has seemed to pick up speed in the last decade.

Brittle snap refers to breakage of corn stalks by violent winds, usually during periods of fast growth. The two most susceptible periods are the fifth- to eighth-leaf stage and from two weeks before tasseling until just after silking, says Steve Butzen, Pioneer agronomy information specialist.

"I don't recall seeing green snap before the 1990s," notes independent crop consultant Earl Raun, owner of Pest Management Co., Lincoln, NE. "It hasn't necessarily been widespread, but when it has occurred, it's caused heavy damage in individual fields. I've seen as much as 60% of a field with snapped stalks."

University of Minnesota agronomist Dale Hicks says the problem definitely has increased in his state over the past five years.

"In 1998 we saw instances of 8- to 10-bu/acre yields because of green snap," he reports. "Nearby yields, not affected, were 180 bu/acre.

"We really can't explain why there has been increased green snap. It seems to be a coincidence of high winds coming at the most susceptible growth stage in those hybrids that are more prone to breakage."

Pioneer's Butzen says there are many theories regarding the apparent increase. "These include an increase in wind speeds compared to normal, development of stiffer-stalked hybrids for stalk-rot resistance and late-season standability, and an increase in the use of postemergent growth-regulator herbicides with adjuvants."

Growth regulator herbicides such as 2,4-D, dicamba and clopyralid, tend to temporarily increase stalk brittleness. Adjuvants enhance the uptake of growth regulators, Butzen explains.

He says wind damage severity can vary within a relatively small area because winds aren't uniform in coverage. Wind currents and downbursts result in narrow zones of destruction.

Ironically, good corn growing practices - early planting, optimum nitrogen rates and corn grown in rotation - have been associated with higher incidences of brittle snap, say University of Nebraska agronomists.

Brittleness is greatest in fast-growing corn under high temperatures and high soil moisture conditions, Butzen points out.

The best way to defend against brittle snap is to select hybrids that have shown tolerance, says Minnesota's Hicks.

"Look for high-yielding hybrids that also have tolerance to green snap," he advises. "Even if a seed company doesn't rate its hybrids for green snap, that information is available. You may need to ask for it."

Pioneer rates its hybrids on a scale of 1 to 9 for brittle snap, with the higher scores indicating less risk.

"But it's important to remember that the risk scores do not reflect injury due to herbicide interaction," says Butzen. "That risk can be reduced by early application, plus proper rates and application methods."