Apr 12, 2012
Ice can save your blueberries during a freeze

When the mercury drops below freezing, blueberry growers may want to try turning on the sprinklers, said Mark Longstroth, a small fruit Extension educator with Michigan State University (MSU).

Like other plants, blueberries responded to the early warm spell across the country and started to bud out and bloom. Like other growers, blueberry growers worried about possible freezes and damage leading to loss of crops and income, Longstroth said.

On April 5, Longstroth gave a talk at MSU’s Trevor Nichols Research Complex, during the 2012 Extension Kickoff Meeting, about using sprinkler irrigation systems to protect blueberries from freezes at bloom.

“Blueberries, like all the other fruit, took off during the warm summer-like weather in March,” he said. “They moved very rapidly during the warm weather, but the recent seasonably cool weather has really stopped blueberries and most of the other fruit in their tracks, with very slow growth.”

Around southwest Michigan, where Longstroth works, the earliest blueberry varieties begin to bloom in early April, but bloom progressed very slowly and most varieties were still in pink bud, he said. That’s the stage when the flowers have emerged from the bud and the petals are pink. Pink bud can handle 27˚ F to 25˚ F with little damage.

“The blueberry leaves have turned red and yellowed a little,” Longstroth said.

How cold can they go?

In bloom temperatures, 27˚ F would cause significant damage, Longstroth said. Growers in Van Buren County are seeing development about four to five weeks ahead of normal for this time of year, due to the early warmth. Normally, growers expect several hard freezes in April, with temperatures at or below 28˚ F.

Common irrigation sprinkler systems apply about 0.1 inch an hour, Longstroth said. This irrigation rate can protect plants down to 24˚ F in calm conditions, 26˚ F in a light breeze or 27˚ F in windier conditions.

“I expect that the freeze on April 6 did cause some damage to some growers’ fields,” he said. “We had cold temperatures in the morning, with lows in the mid-20s, that may have caused damage. Some growers used their sprinkler systems and made ice, and many did not. I generally don’t recommend using sprinklers unless there is open bloom in the field, but many growers will use their systems before bloom as well.”

Sprinklers are very effective under certain circumstances, but can increase injury if used at the wrong time, Longstroth said. Sprinklers used for irrigation do not protect below 23˚ F to 24˚ F. Using sprinklers to prevent freezing injury uses the energy that water releases when it freezes, changing from a liquid to a solid, to keep the temperature in the ice at the freezing point, 32˚ F.

“As long as you keep the ice wet, the ice temperature will stay at 32˚ F,” Longstroth said.

There was not much winter injury in Van Buren County at the time, but Longstroth was told there was some in Ottawa County and to the north.

“At this point in time no significant damage has been done, but we have a long way to go.”

There is a 50 percent chance of a freeze in late April in southern Michigan. If they make it into May, the chance of a freeze drops to 10 percent under normal circumstances, Longstroth said.

By Derrek Sigler, Assistant Editor

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