NC State Extension’s forecast helps strawberry growers avoid frost disaster

CorrespondentApril 7, 2013 

Barclay Poling doesn’t want to make a habit of 4:30 a.m. weather monitoring for North Carolina strawberry growers, but he and his advisory service are there when they need him.

They certainly needed him late in the day on March 21 and early the next morning: A perfect storm of low temperatures, strong winds and dry conditions resulted in the most potentially damaging conditions for the state strawberry crop since the Easter freeze of 2007. But thanks to Poling’s website, growers had several days’ advance notice.

“The weekend of the 17th, we started seeing the 22nd (Friday) showing up as a problem,” said Poling, the N.C. State professor emeritus and Extension specialist for strawberries in the department of horticultural science. “That gave us the luxury of having a little more time to break the news to the industry.

“For the first time, I actually used some headlines in my advisory. I would have a picture of the entire strawberry plant with some beautiful blooms on it and write, ‘These are all gone if you don’t do such and such.’ That was the first week of the season in which the North Carolina crops had, generally speaking, a lot of blooms at risk.”

The website – which serves five states with Internet and email alerts, weekly and 16-day forecasts, even 30-day outlooks – has only been public since Feb. 8. But growers were already locked into it when the big frost hit. N.C. State Extension IT specialist Scott McCollum said the site’s 935 page views on March 22 were more than triple the number of average daily views, with a healthy average time spent of four minutes.

Growing stakes

The site combines Poling’s extensive experience and knowledge with information from the State Climate Office of North Carolina and reliable private weather tracking services AWIS (Agricultural Weather Information Service) and SkyBit, providing specifics and detail that he says are unheard of in a university service.

Among the features on the site, currently focused on the Coastal Plain and Piedmont until blooms become more of a factor in the mountains: forecasts of conditions including temperature, winds and dew point – by hour – for specific locations.

North Carolina Strawberry Association Executive Secretary Debby Wechsler said weather monitoring technology previously saved growers more than $4 million in lost crops during frost events. So given the huge economic stakes and projected weather patterns in an already challenging climate, Poling’s service comes at a good time.

Wechsler said that based on the value of the crop harvested – $29.4 million in 2012 – the state ranks third in the U.S. behind only California and Florida. The N.C. Department of Agriculture and Human Services says the state harvests about 1,800 acres of strawberries each year at about 200 farms, ranking it fourth in that category.

Ryan Bowles of the state climate office told a conference in February that growers can expect more extreme weather in frequency and intensity. Poling said North Carolina is already “one of the world’s most challenging climates for strawberry growers because of all of these frost and heat events during the bloom season.”

Douglas Patterson of China Grove-based Patterson Farm relies on the detailed specifics of Poling’s service.

“His weather monitoring program tailors the temperature profiles to each grower’s location,” he said. “This is very helpful in that our temperatures may be up to 5 degrees lower than Charlotte lows that are predicted by Charlotte-area weather services.

“We print out his report each day and give it to our crews for nighttime frost protection. They use the report to schedule the amount of help that is needed.”

‘It was just incredible’

The March 21-22 scare posed a strong challenge for Poling and growers.

“I hadn’t had to match my wits against one of these things in a while,” he said. “I was up at 4:30 on Friday morning, calculating for different areas of the state when the growers could shut down (sprinkling).

“The dew point kept falling after sunrise. I’ve not seen that one before. It was just incredible. ... And winds came up. So you had two factors: drier air getting drier, and winds. So if you shut down sprinkling at 8 o’clock in the morning, even though the sun was now up, the crop could actually freeze up again.

“And we had people in the Sandhills registering 20 degrees that night, which was really shocking.”

Proper timing and duration of sprinkling are “everything,” Poling said.

“The air temperature and something we call the ‘wet bulb temperature’ are very important in terms of decision-making when sprinkling under these very dry conditions. When the air temperature was 40 the other night at 7 o’clock, the wet bulb was already down around 30. We have a fixed rule that we learned the hard way from some terrible setbacks years ago, which is: We start (sprinkling) before the wet bulb temperature hits 30 or 31.

“That night, growers were starting irrigation at sunset. Years ago, growers would wait until the air temperature was near the freezing mark – but what they didn’t know was that when they started at that air temperature, when the blossoms were exposed to the first rounds of irrigation, the water was actually not able to freeze up in that phase-change from liquid water to the frozen state.

“Under winds and very low humidity, what happens is, the initial irrigation goes for cooling purposes – a very powerful process. So when the plant gets hit with that water, you’re cooling it down, and that can kill it instantly.”

Poling said the typical watering session is from around 5 a.m. until shortly after sunrise, three hours at most – but that the March 21-22 event required an average of 12 to 13 hours.

Keeping what they have

John Vollmer of Vollmer Farm in Bunn, in Franklin County – one of the coldest areas in the middle Piedmont – said he came out of the frost-freeze “beautifully” with the help of the service. The site is so important to growers that he’s concerned about what will happen to it when the 59-year-old Poling retires.

Poling said he’s just happy to have been coaxed out of retirement last year to lead the service. For now, he’d rather focus on the April-May growing season with its growing heat – “if we can only get there. Last year in Raleigh, we were picking berries by March 23.”

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