Freeze Forecast?

Freezing weather remains a threaten for fruit, nursery and farm crops.

Published on: Mar 23, 2012

Peach trees in the MU research orchard are set to bloom this week says Michele Warmund, University of Missouri horticulturist. That is at least three weeks early.

There's a problem with that beautiful scene of the fruit crop blooming. Killing freezes can occur from now until the "last-freeze date" well into April.

Blossom set determines the bounty of the fruit crop. An early growing season is occurring across the state with fruit, nursery and farm crops.

"There could be a lot of dead flower buds with major crop loss if temperatures plummet," Warmund said after working with her fruit trees and berry brambles at the MU horticultural plots.

Freezing weather remains a threaten for fruit, nursery and farm crops.
Freezing weather remains a threaten for fruit, nursery and farm crops.

An MU climatologist said, "Arctic blasts could return with a slight shift in the jet stream, which has stayed well north in Canada this winter." Pat Guinan of MU Extension reports this winter to be one of five warmest in more than 100 years.

Based on records, severe winter storms can occur in mid-Missouri until at least the second week of April, Guinan said. Frosts could occur later.

Many agriculture specialists recall the Easter freeze of 2007. Millions of dollars in crop loss hit orchards, hay fields and newly sprouted corn.

Rob Kallenbach, MU forage specialist, said the April 2007 freeze killed much of the state's alfalfa. This week he visited a mid-Missouri dairy farm with a fall-seeded alfalfa field. The forage already stands 4 inches tall-and vulnerable.

Growing points on alfalfa, as with all legumes, are at the top of the plant. The tender tip can be killed when temperatures drop below freezing. "Grass can withstand freezes as the growing point remains at ground level," Kallenbach added.

Guinan said median dates for freezing temperature thresholds are based on moving averages of freezes for the last three decades. "'Median' means that half the time, the freeze can occur after that date."

The median dates for temperatures dropping to 28 degrees Fahrenheit are in the last 10 days of March in the Bootheel to the first week of April across southern and central Missouri. Median dates extend into the second week of April over northern counties.

Moderate freezes occur at temperatures between 24 and 28 degrees.

MU crop specialists worry that daily high temperatures in the 80s by mid-March will tempt corn farmers to start planting early.

In that big freeze of 2007, when temperatures dropped to the teens, thousands of acres of corn had to be replanted in southeastern Missouri.

Peaches in Missouri are one of the most vulnerable crops because of their early blossom set, Warmund said. Apples flower later.

In the 1980s, a cold decade, Missouri had only a couple of full peach crops, she added.

Peach blossoms can withstand a light frost and set a crop. When temperatures drop into the low 20s, heavy damage can result.

"Peach trees can retain 10 percent of their blossoms and still make a full crop. I've been fooled when it appeared all buds were frozen, yet the trees set fruit," Warmund said.

"We don't grow apricots, because they blossom even earlier," she added. "They are already in bloom in southern Illinois."

On her research plots, mulch has been removed from strawberry beds to let sunshine warm the soil. However, foam blankets are kept nearby in case of freeze warnings.

Homeowners can protect vulnerable plants with protective covers at night. However, farm crops can't be protected.

Guinan cautions that freezes can vary across local terrain. Low temperatures can vary by more than 10 degrees from the bottom of a valley to a nearby hilltop. Urban areas tend to be warmer than rural areas.

On April 8-9, 1973, a blizzard hit northern Missouri with snow up to 12 inches, winds over 40 mph and drifts 10 feet deep. Cows and calves died.

"The records show that winter weather can occur well into April," Guinan said.

The National Weather Service coordinates with Warmund and Guinan as they refine possible freeze warnings for agriculture across the state.

The MU orchards are on the Horticulture and Agroforestry Research Center on river bluffs west of New Franklin, Mo. It is one of 20 research sites of the Agricultural Experiment Station across the state.

Source: University of Missouri Extension