Tips To Manage Winter-Damaged Blueberries

Flowers on this blooming plant are iced over during a freeze. (Photo credit: Bill Cline)

Blueberry growers in North Carolina had quite a rollercoaster start to the 2017 growing season. Warm temperatures started the season early — three weeks, in fact, says Bill Cline, Researcher and Extension Specialist for the Department of Entomology and Plant Pathology at North Carolina State University.

Then, in March, freezing temperatures came. While growers were able to use overhead irrigation to irrigate many blueberry bushes, some low-chill varieties such as ‘Star’ and ‘Rebel’ had bloomed early and set green fruit. Those proved harder to protect, especially in wind-borne freezes.

“Anything that was in full bloom or green fruit stage we pretty much lost,” he says.

Cline says management of these freeze-damaged berry bushes will vary, but it is a good opportunity for growers to give those plants extra TLC.

Delay Bloom Next Year
First, Cline suggests growers consider making summer mow-cuts to remove twiggy growth. He says once crop insurance adjusters are finished assessing the damage is a good time to remove all freeze-damaged wood.

“Go right in and mow them back pretty hard with the idea that you’re setting up the kind of berry you want for the 2018 crop,” he says.

This mow-cut will have an added benefit — it will delay bloom time for the 2018 season. Cline says he noticed those bushes that were mowed in 2016 seemed to come out of this year’s freeze better off than those plants that were not

Bill Cline suggests growers consider making mowing-cuts that will help delay bloom next year. You can mow your field after harvest or after a freeze. (Photo Credit: Bill Cline)

mowed.

 

So, that mow cut will act as extra freeze protection next season.

Follow Up With Fungicides
Freeze-injured tissues are going to be more susceptible to fungal infections, Cline says. Growers should spray for phomopsis twig blight, flower blight, and botrytis.

“Where you have blighted flowers or blighted twigs, that dead, injured tissue provides an initial food base for botrytis gray mold to get started, and then that fungus and phomopsis will blight the twigs,” he says. “You have this portion of the crop that survived that will potentially be killed by fungi if you’re not controlling it.”

Change Approach to Fertilizing
While a nutrition plan is still important for damaged blueberry bushes, Cline suggests growers consider distributing those applications differently.

“[Growers] have an opportunity to spoon-feed the fertilizer to make smaller applications more frequently,” he says.

Cline suggests growers fertilize in smaller amounts more frequently in fields where the crop was lost or reduced.

“In a normal year, granular or liquid fertilizer applications using ground equipment have to be curtailed once the berries start to size up, otherwise the tractors passing down the rows knock off too many berries,” he said. “This forces growers to apply lots of fertilizer up front, early in the season. By contrast, in a freeze year, fertilizer can be used much more efficiently on an as-needed basis.”

A grower could spread the applications throughout the spring and summer, which would be more economical for the grower and more effective for the plants.

A cross section of damaged ovules in a developing berry flower. (Photo Credit: Bill Cline)

 

“You still would like to stop or have most of the fertilization on by the first of July,” he says.

Growers in Southern states like North Carolina, where phosphorous is limiting, may apply some diammonium phosphate in August if the need is indicated by soil test results, but Cline says that’s about as late as growers should be fertilizing.

Think About Variety Choices
“Folks will take a long, hard look at what they’re planting going forward. This might put the brakes on cultivars such as ‘Star’ and ‘Rebel,’ anything that gets out really early,” he says.

He says growers may put in irrigation systems that put out a lot of water to protect those susceptible varieties like ‘Star.’

“Typical overhead systems in North Carolina currently apply the equivalent of 0.15 inches of water per hour,” he said. “Higher rates will be needed if we are going to protect against the sort of wind-borne freezes that typically occur in March.”

These days, growers have anywhere from four to six or more cultivars to balance out risk and to extend the harvest period. This is a change from years past when a variety such as ‘Croatan’ once made up 60% of the acres planted in North Carolina.

“I go look at those ‘Croatan’ bushes on our research farm, and they’re just now breaking dormancy. They’re just now [at the end of March] emerging from the bud, from the wood. Is it a change in our weather or is it a change in our cultivars? I think it’s a little bit of both.”

‘Duke’ is another variety that may fall into favor with growers looking to get into the market at the end of May. The intriguing part is that although ‘Duke’ ripens early, it blooms later than ‘Star’
or ‘Rebel.’

“It has a short bloom to ripe interval. That’s a really desirable characteristic,” Cline says. “Are there other cultivars that would do that?”

This is the second year in a row where low-chill varieties bloomed early and growers sustained crop losses. In light of this, Cline says growers will adapt to manage the risk of some of these low-chill varieties.

“We’ve got some pretty smart growers. Growers understand their risk, and they tend to grow many cultivars,” he says. “How do you manage that risk? Do you not plant that cultivar, or do you plant it and then summer mow it so that it doesn’t bloom quite so early?”

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