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April 4, 2007

Wicked winter weather gone, but not for long

WEST LAFAYETTE, Ind. - The unusually warm weather ended on Wednesday (April 4), and Purdue University crop experts are concerned about the cold front's impact on crops.

An extreme temperature change toward freezing with lows in the 20s poses a risk to Indiana's alfalfa and wheat crops. The lowest temperatures from this cold front are expected to occur Friday (April 6) evening and into Saturday (April 7) evening, which is when plant damage is most likely to occur.

"We have had enough warm weather that plants have generally lost their winter hardiness," said agronomy specialist Jeff Volenec. "Most plants will not be damaged at temperatures above 25 degrees Fahrenheit, but once temperatures drop below that point the damage gets progressively worse."

In addition to the low temperatures, plants also will be affected by their current growth stage and the amount of cloud cover.

"If there is a clear, cloud-free night following the passing of this cold front, damage will be worse because plants near the soil's surface serve as a source of energy that is lost in space," Volenec said. "The clouds act as a blanket by minimizing energy losses from the plants' surface, therefore, the plants remain warmer."

Wheat and alfalfa damage are the primary concerns for growers. Approximately 450,000 acres of winter wheat was planted in Indiana last fall and 360,000 acres of alfalfa is growing at this time.

The amount of damage will depend, in part, on the plants' growth stage, said agronomy specialist Shawn Conley.

"For wheat in the tillering stage, temperatures will have to drop below 12 degrees Fahrenheit before growers will see a yield effect," Conley said. "For wheat in the jointing stage, moderate to severe yield loss will occur at temperatures lower than 24 degrees for more than two hours."

Growers in the southern portion of the state where wheat may be close to jointing should pay the most attention to this cold spell, Conley said. 

"Shortly following the freeze, growers need to evaluate the field," said Keith Johnson, another agronomy specialist. "Take into account the soil type, moisture level and growth stage because field variability will have different responses."

When evaluating alfalfa, look at the crown and tap root, Johnson said. It's a good sign if the tap root retains a beige/white, solid color and not good if it appears water-soaked or becomes brown or black in color, he said.

Also in the days following the freeze, it will be common for emerging leaves to take on a bleached appearance, Johnson said. If this occurs, it is only a short-term response.

Conley said that knowing the growth stage of the crop plus the temperatures endured for a specified time help in determining yield loss.

While the current cold snap isn't good news, another freeze a week or two following this one would be worse, Volenec said. Plants may tolerate and survive one freeze event, but are less likely to survive a second.

Writer: Julie Douglas, (765) 496-1050, douglajk@purdue.edu

Sources: Keith Johnson, (765) 494-4800, johnsonk@purdue.edu

Shawn Conley, (765) 494-0895, conleysp@purdue.edu

Jeff Volenec, (765) 494-8071, jvolenec@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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