Fort Dodge Messenger, IA
04-14-07
Producers ponder freeze damage to fruits
Next few days critical to crops
By DARCY DOUGHERTY-MAULSBY, Messenger correspondent
Northwest Iowa Grape Growers meeting is 6 p.m. Monday at the Richard Black farm, 3228 Xenia Ave. near Farnhamville.
JEFFERSON — With this year’s pre-Easter cold snap biting on the heels of
March’s unusually spring-like weather, fruit growers across Iowa have been checking buds on their apple trees, grapevines and other fruit crops to determine the extent of the damage.
“I have some damage, but I also found quite a few green buds, so we’ll have apples this year," said Jerald Deal, who owns the 45acre Deal’s Orchard near
Jefferson.
For many fruit growers, the recent cold weather provided an unwelcome flashback to the bitter spring of 2005. Richard Black, who raises grapes near
Farnhamville, recalled the killing frost of May 15, 2005, when the mercury plunged to nearly 23 degrees Fahrenheit. Ironically, it’s not typical in Iowa to get this many severe frosts or freezes during the spring, said Dr. Paul Domoto, a professor of horticulture at Iowa State University.
“Often these events only happen once every 10 to 15 years. I’ve been researching apples in Iowa for more than 30 years and have seen four of these events, with two coming in the last few years."
Warm days cause trouble
What’s most at risk in a typical cold snap are plants’ succulent (moist, fleshy) tissues. The colder, longer, and more abrupt the snap, the greater the risk to those tissues. While buds are usually just beginning to emerge this time of year, many plants and trees jumped about two weeks ahead of schedule due to unseasonably warm weather in March.
Apples’ vulnerability to cold temperatures depends on what stage of development the trees are in. When buds are just beginning to swell and trees are in the silvertip stage, 15 degrees F will injure 10 percent of the crop, while 2 degrees F will injure 90 percent of the crop, Domoto noted.

When the recent cold snap hit, many apple trees in central Iowa had advanced to the green-tip stage or half-inch green-tip stage (when leaf tissue begins projecting from the bud). At the green-tip stage, 18 degrees F will injure 10 percent of the crop, while 10 degrees F will injure 90 percent of the crop. At the half-inch green-tip stage, 23 degrees F will injure 10 percent of the crop, while 15 degrees F will injure 90 percent of the crop.
By the time apples reach the tight-cluster stage where blossom buds are mostly exposed, 27 degrees F will injure 10 percent of the crop, while 21 degrees F will injure 90 percent of the crop. At Deal’s Orchard many of the trees were in the half-inch green stage to the tight-cluster stage.
At ISU’s research farms, Domoto said temperatures ranged from 12 degrees F at
Sutherland to 18 degrees at Muscatine on April 7, one of the coldest days of the spring freeze. Fortunately, the strong winds that buffeted Iowa helped limit the damage. This is attributed to the resulting advection freeze, which occurs under windy co nditions when a large, dry, cold air mass moves in. “An advection freeze is better than a radiation freeze, where a lack of air movement allows cold air to settle near the ground," Domoto explained. “When that happens, buds can become colder than the air temperature."
The wind was a blessing, Deal added, because it also helped dry out the apple buds, leaving less moisture to freeze.
Cold increases injury risk to berries, grapes
Apples aren’t the only fruits that suffer when the mercury plunges. For cherry trees in the green-tip stage, 25 degrees F will injure 10 percent of the crop, while
14 degrees F will injure 90 percent of the crop. Iowa’s peach trees, however, may take the biggest hit this spring. “I heard that peach trees in southern Iowa were in bl oom, and at 27 degrees F you’ll see a 10 percent kill, while 24 degrees F leads to a 90 percent kill," Domoto noted.
While Iowa’s strawberry crop should be safe since growers can keep the plants covered with mulch, raspberries in some parts of Iowa were breaking buds when
Mother Nature unleashed her frigid blasts, creating the potential for damage.
Grapes are also exhibiting signs of injury. Domoto noted that 50 percent injury can result when grape buds enter the first-swell stage and temperatures drop to
18 degrees F.
While warm temperatures in March jumpstarted the growth of Black’s wine grapes, the cold spell shut everything down and prevented the buds (some of which looked like they were just beginning to swell) from developing. Black, who is beginning his fifth year of growing grapes and is expanding to three acres under production, won’t know the extent of the damage until the buds begin to

break. “We’ll need several days with temperatures in the upper 50s or 60s before they’ll begin to grow. Hopefully the damage will be minimal."
Next few weeks critical
While all of Black’s wine grapes are cold-climate varieties, they aren’t immune to
Iowa’s temperature fluctuations. Although the La Crescent variety was developed in Minnesota, it’s the first of Black’s five grape varieties to bud, making it vulnerable to the warm-ups that can occur in Iowa in February and March.
The next few weeks will be critical for both Black’s crop and Deal’s apples. While corn and soybean growers can rely on crop insurance to help them overcome production challenges, fruit growers aren’t so fortunate. Deal noted that although a minor safety net is available, apple growers only become eligible for payments if they experience a 50 percent loss, and even then the amount that’s paid per bushel is low.
“We’ll be walking on pins and needles for the next several weeks," said Deal, who noted that the 2005 freeze during the first week of May when the trees were in full blossom resulted in an apple crop that was less than 30 percent of normal.
Learn more
If you’d like more information on growing fruit in Iowa, ISU Extension offers “Fruit
Cultivars for Iowa" (PM 453) and “Growing Fruit in Iowa"(PM 1788). ISU
Extension will also be hosting a meeting of the Northwest Iowa Grape Growers
(wh ich is open to the public) at Richard Black’s farm near Farnhamville at 6 p.m.
Monday. For more details, contact Jerry Chizek, Calhoun County Extension director, 712-297-8611 or jwchizek@iastate.edu.
Contact Darcy Dougherty-Maulsby at (515) 573-2141 or editor@farm-news.com