Strawberry Mania

After an extreme winter of weather, it has been a challenging growing season for strawberry farmers. Learn how science is helping farmers grow their crops despite unusual winter weather.

DURHAM - There are a lot of crops that grow well in North Carolina. Tobacco, cotton, soybeans, peanuts and sweet potatoes are just a few of the state’s most popular and most valuable crops.

Strawberries are not a crop that is supposed to grow in this climate. But the plants do grow in the Tar Heel state and they grow well, thanks in no small way to science giving Mother Nature as well as the state’s farmers a helping hand.

In fact, North Carolina farms produce about 19 million pounds of strawberries each year. The crop is worth about $30 million. That ranks North Carolina third in the nation for strawberry production. However, the strawberry production that is accomplished on North Carolina’s roughly 200 farms is unique. That’s because most of the 1800 acres are devoted to direct to consumer sales, which means customers are able to pick their own strawberries or visit roadside stands.

“North Carolina is able to grow strawberries because of all the science and technology that is devoted to the crop,” said Debby Wechsler, Executive Secretary of the North Carolina Strawberry Association. “It’s really what is known as intense management. It takes a lot of care. It’s not like you just throw them out and let them grow. Farmers have to be on this crop all the time, from when they prepare their farms and set their crops and then all the way through harvest.”

California and Florida lead the nation in strawberry production, and the growers in those states produce a crop from their plants every two years. North Carolina ranks third in production, but because of the intense management of the crop, North Carolina farmers are able to produce a crop every year.

A good example of that intense management can be seen on the Waller Family Farm in Durham, NC. Mark Waller farms 40 acres of strawberries on what used to be a tobacco farm. Customers can pick their own strawberries or visit the market he runs during the strawberry season, which can run anywhere from April through June.

“Right after we close the operation down for the season, we take up all of the irrigation hoses and row covers and we also cut everything down and plow it under,” Waller said, as he knelt down to examine some still-green strawberries that will ripen in about one week. “I want to kill any pests or problems that could be in this field so they don’t harm next year’s crop. I will then send soil samples to the state to be analyzed.”

Soil scientists will tell Mark what needs to be done to his soil, such as adding lime to adjust the PH as well as fertilizers and other nutrients. The soil is then tilled again. Afterwards, the rows in which the plants will grow are rebuilt, the drip tape for irrigation is installed, and the plastic is added to cover the rows. The black plastic and heavy irrigation allows the roots to grow and the plants to set through the winter.

The strawberry plants need to be in the ground by the end of September or the beginning of October for the crop to be ready by spring. If all goes well, the plants begin to flower in March.

“Once we see about eight-to-ten blooms per plant, we really pick up the intensity around the farm,” adds Waller. “Not only are we fertilizing, but we are also really watching for frost.”

And that’s where North Carolina State University Professor Emeritus Barclay Poling’s research comes in.

“It depends a lot on the environmental conditions,” Poling explains, as he bends over a row of strawberries on the Waller farm. “If it’s a real humid with lots of moisture in the air type of night, we can get frost or ice crystals on the bloom and we’ve killed blossoms as high as 31 degrees, which is really interesting. If it’s a dry night, with a low dew point, in those conditions the flowers can super cool to as low as 27, so that’s quite a range.”

Poling has found the average critical temperature for strawberry blooms in the state is 28 degrees. If the blooms get much colder than that, they will either stay dormant and wait for warmer weather, or possibly die if the cold persists. Because the blooms are the most vulnerable tissue for the strawberry plant, and the most critical to a successful harvest, Poling compiles a wealth of weather information into an alert system to warn farmers of significant weather events during the all-important spring growing season.

“I work with pretty advanced weather information to alert growers, and I can give them a lot of information right up to the weather event, but then this is all about onsite monitoring,” said Poling. “The farmer needs to become his own weatherman and plan ahead for what is coming. He also needs to come out to his fields and use this device to check the blossom temperatures.”

The device is a handheld thermometer, which Poling also helped develop. Electrodes at one end of a wire are inserted into the strawberry blossoms while the other end of the wire is connected to a digital thermometer. The device reads the temperature of the strawberry blossom. The farmer needs to combine the plant temperature readings with the current conditions and the forecast, to decide whether to cover his crops or irrigate them to protect from frost.

The device is also important as the weather gets warm. If the blossom temperature gets too high, the farmer needs to irrigate to cool his plants.

As for frost protection, some farmers cover their plants, allowing the frost to form on the thin agriculture cloth rather than the plants. Mark Waller irrigates, taking advantage of the fact that when liquid freezes, it releases energy in the form of heat to the fruit, which protects it from the cold.

“It’s more than just temperature you have to be concerned about, because you also have to look at the dew point along with what might be happening as the night goes on,” Waller said. “For example, if it is really dry air and it’s going to get cold, we’ll start irrigating before it gets to freezing because you don’t want to shock the plants. We monitor a lot of things and then determine when it is best to cut the irrigation on.”

The irony is that for all of the help science has provided to North Carolina’s strawberry farmers, Mother Nature is still full of surprises and challenges.

“It’s sort of like going out on a hike and seeing a sign that says 'unmarked trail,'” said Poling as he smiles and plucks a berry from a plant to examine it. “For all we can monitor and plan for, every strawberry season is an unmarked trail and so you go out and anticipate what might be happening but you are never sure. So I help the growers anticipate that this is something totally new or this is something we saw five years ago.”

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