MINNEAPOLIS – February 15, 2012 – They’ve seen this movie before and it’s not their favorite. There may be record-setting warm temperatures over the winter and early spring, but there is a chill among many tree fruit and vine growers who are concerned this could set up a repeat of late frosts.

Among those with a wary eye on the weather are John Jacobson, Minnesota apple grower, and Joe Dietrich, whose apple orchard is in Michigan.

Jacobson’s 150-acre Pine Tree Apple Orchard is at White Bear Lake just northeast of St. Paul. A second orchard is about 30 miles away near Preston, about 30 miles south of Rochester. His brother Bill Jacobson and son J.P. also are part of the family orchard operation.

“We’re at least a month ahead of where we should be in terms of the phenology of the crop development,” said Jacobson. “By the third week of March the trees already had small leaves and buds. I’m worried what will happen if the weather goes seasonal on us and we have a late frost. As each day moves the trees farther along they lose more ability to withstand colder temperatures. In the back of my mind I’m thinking back to 2010 and working on Plan B.”

For Jacobson and Dietrich, along with some grape and citrus growers, “Plan B” includes carefully timed applications of a unique potassium and sugars formulation that helped them avert disaster two years ago. When large fans and sprinkler systems aren’t available or are too costly, growers have found that fruit and vine crops can gain a few degrees of protection when Potassium Dextro-Lac (KDL) is applied a few days or even hours ahead of the frost event. It’s an unusual approach for when the frosts are damaging but not extreme.

“The last three years we really haven’t had a statistically ‘normal’ winter,” Jacobson says. “Last winter was unusually cold and snowy, but in 2010 we had another really early spring, with bloom on May 1 instead of May 10 to 15. In 2011 bloom was May 22 or 23, so this year the pendulum has swung back the other way. I call what happened in 2010 the Mother’s Day Massacre. But we had pretty good information that it would get cold. Some trees were still in bloom, some blossoms had fallen.

“It was the first time we used KDL that way, though we’d heard it could help plants withstand frost, so 3 or 4 days ahead of that Saturday night frost we sprayed our high-value apples to give it a try. The temperatures fell to the low to mid-20s at White Bear Lake and Preston, but both orchards came through very well so I’m confident we gained a few degrees. We were very satisfied with the results. This year I’m looking at the forecasts and will be prepared to spray again.”

Dietrich orchards survived ‘Mother’s Day Frost’
Joe Dietrich is co-owner of the 800-acre Ridgeview Orchards near Conklin along with his brother Al Dietrich and their sons Ryan and Dan. Joe says their trees could get set up for another tough freeze situation this year because this has been the second warmest winter on record in Michigan. As Jacobson said it is reminiscent of how the apple trees were hitting bloom ahead of the Mother’s Day calamity in 2010 when a warmer March was followed by long-cold April and then a series of freezing nights the first week of May. Dietrich says KDL greatly reduced the damage to his crop and trees when the series of freezes began

.“I applied it on April 28 at tight cluster, and again on May 4 at pink,” Dietrich recalls. “Then the freezes came during the week after that, with the last one around May 10th. We were in bloom then and I believe the temperatures went down to 26 to 28 degrees. We grow about 20 varieties and had about 580 acres then, and while we had a little damage it was much less than what most of the other orchards had that spring. So we gained at least a few degrees of protection.”

Other growers did not fare as well. The overall size of the Michigan apple crop was sharply reduced in 2010, along with grades for much of the crop. The long bloom period, poor pollination, and poor fruit set took its toll.

“We’ve used the sprays at least three or four different years, and it has helped,” said Dietrich. “I hope that this year we will have some cold weather again well before we get into spring so the trees won’t progress in fruit development too early, or maybe we’ll be spared the late frosts.” Dietrich, who has been growing apples for 30 years, is in the 5th generation on the Ridgeview Orchards farm, which began in 1853 and is 10 miles north of Grand Rapids in the Fruit Ridge area.

Grape growers face spring and fall frost threats
Father south at Baroda, near Lake Michigan just below Benton Harbor, Dan Nitz’s 450-acre Arrowhead Vineyards also faced damage during the Mother’s Day frosts. About 60 percent of his grapes go to more than 40 wineries in 19 states. The other 40 percent are Concord juice grapes for Welch’s.

“Michigan is famous for frosts, and we get one every few years,” said Nitz, third generation of his family to grow wine and juice grapes. “Ahead of the last frost, two years ago in mid-April, we used the KDL on about 60 acres of the Concord juice grapes in a lower elevation. We weren’t worried as much about the wine grapes up higher. But the vines down lower are in a more frost-prone area.

“A full crop of those grapes is about 8 tons to the acre, and that year we wound up with 4 tons per acre. That may not sound good, but our neighboring vineyards on the same elevation had no crop at all. So we at least covered our expenses and broke even versus losing completely. It’s like that potassium provides an inner antifreeze for the grapes."

Don Dinesen worked in California about 25 years before moving back to Minnesota and transplanting the interest in viticulture he developed while out West. He has been more concerned about early fall frosts in his area of Minnesota, particularly after the freeze last September 15. His 3,000 grape vines were vulnerable to damage, so he sprayed them with KDL about 12-15 hours before the frost.

“I walked out into the vineyard about 5 a.m. and found the temperature was 28 degrees,” said Dinesen. “While the grass near the house was so covered with frost that it crunched when I walked across it, the grass between each of the rows of grapes was wet, with no frost or ice at all, which I attribute to the overspray. “We have two adjacent blocks of Marquette grapes, and since one of them is still a year from meaningful production, we didn’t treat them.

“During that day and the next, I surveyed all the grapes, both treated and untreated. I had not suffered any appreciable frost-related damage to the treated vines, but had total loss of leaves on the untreated vines. We were able to keep the treated block of grapes healthy and picked a good crop three weeks later. I don’t think we could have done that without the KDL.” The grapes salvaged from the damaged vines went into a blush wine, “which also turned out to be a very good experiment because it opened up new possibilities for use of our grapes.”

Dinesen said he uses KDL for its primary purpose, sequential fall sprays to improve consistency and elongation of grape clusters, the sugars, and other traits, so he had plenty on hand. It came in handy for a neighbor who asked to use some of his KDL in a very last-minute effort to defend her grape vines. Even though it was sprayed about 5 p.m. the evening of the frost she reported great success and was very pleased with the survival of her leaf canopy despite temperatures that froze nearly everything else in her vicinity.

Cherries and citrus escape damage
In California, frost is less a persistent threat in most areas. The vineyards and orchards are often large enough to have fans and sprinkler systems. But that frosty weather in 2010 went far beyond the northern Midwest, as California Pest Control Advisers well recall.

“A ranch manager we worked with was very concerned about a cherry crop when we were due to be hit with a freeze the second week of April in 2010,” said Jon Tecklenburg, whose Tecklenburg Ranch Services is in Lodi. “He treated with KDL and that block of cherry trees had a 100 percent crop, but he ran out of spray and didn’t catch the two outside rows. Those two rows had probably a 30 percent crop and provided an inadvertent check for the spray experiment.”

Tecklenburg has been working in agricultural research and product development since 1965, has farmed professionally during his career, has conducted crop loss investigations for the Federal Catastrophic Crop Loss Program, and often conducts independent agricultural forensics work for clients.

He recalls another frost situation three years earlier when in mid-February the area had 10 straight days where the temperature never got above freezing.

“A grower was willing to give up his crop if he could save a block of young citrus trees, and in that10-day period we made two applications of KDL,” said Tecklenburg. “The grower still harvested 85% of his fruit, and his trees showed no damage from frost. But across the street the citrus trees showed considerable damage.

“These are the kind of frost events growers worry over until along about April 25. I consider that the date when crops are usually safe, though we’ve had a lot of frosts the last week of April during the last 30 years and we’ve even had frosts as late as May 5. Cherries hit beautiful bloom in mid-March, and grapes will be budding along about the first week of March as they break dormancy.”

Tree fruit expert cites speed of protection
Bob Purvis is chair of the Apricot Interest Group of the North American Fruit Explorers and the NAFEX secretary. He has grown apricots and various tree fruit crops in Minnesota but now does that in Homedale, Idaho where there are one or two late spring frosts each year at his Purvis Nursery & Orchard. He said the speed of the KDL protection for his apricot trees and other crops is striking.

“The potassium passes very quickly, in a matter of minutes, into the plant tissues,” said Purvis. “That likely is because of the unique way the potassium is formulated with the lactose and dextrose sugars.” Purvis believes the plants are hungry for the carbon in the sugars as well as the potassium. Agro-K Corporation, which developed KDL, said research indicates it helps balance nutrients within the plants as the potassium polysaccharide molecules are taken up directly through the cell walls and then metabolized and mobilized by the plant’s vascular systems.

Purvis recalls what happened last April when temperatures were cooler than average in southwest Idaho, as recorded in his daily journal kept for the past 50 years:

“Full bloom on apricots was on the average about April 10 although it varied a bit from cultivar to cultivar. This is unusually late. Historically, apricot full bloom averages about March 20 in this area. The first application of KDL was about April 10 and on April 19 our morning low on the home site was 28F. On the 20th it was 27F, and on the 21st, 41F. On the 22nd it was 27F but in the orchard, at a lower elevation, it was 25.7F. The evening of April 22 I again sprayed KDL at the rate of 3 oz./gal., mixed with an equal part of household vinegar (3 oz./gal.) to neutralize its alkalinity, on my apricot, peach, cherry, plum, and pear trees. There was no phytotoxicity to leaves or blossoms evident in the days that followed either application.

“The low on the home site the morning of April 23 was 25F, but in the orchard it was 24F. By this time, most apricot trees were at or very close to petal-fall. For commercial apricot cultivars at full bloom, a half-hour at 27F will cause mortality to 10% of the blossoms; a half-hour exposure to 22F will cause 90% mortality. The corresponding figures when the tender fruitlets are encased in the shuck are 27F for 10% mortality and 24F for 90% mortality. When naked and exposed, 28 and 25 are the corresponding 10% and 90% temperatures.

“From this, assuming 23F would be the 90% mortality temperature as petal-fall ends and shuck stage begins, it would appear that with no protection about 70 to 80% of the fruitlets should have been killed by the 24F temperature we had the morning of April 23. The good news is that with the exception of the three most cold-hardy Canadian apricot cultivars, which were well into shuck stage at this point, we had an excellent crop of apricots, and I spent many hours thinning the fruits. It was impossible to find any evidence of damaged or dead fruitlets based on cutting open ovaries on the lowest fruits on the lowest trees in the orchard. We had a good crop of cherries, peaches, plums, and pears as well.”

Purvis says last spring’s experience simply corroborates his observations the past six years in Minnesota and in Idaho that at full bloom apricot varieties get about 5 to 6 degrees protection with KDL. Purvis says KDL may make it possible to get crops of apricots in areas that are troubled by fluctuating spring temperatures and late frosts, in seasons when it might otherwise be impossible.

Purvis, who formerly worked as a commercial horticulturist in the Yakima Valley of Washington, has grown, tested and reported results with a wide spectrum of nursery stock in his small-scale orchards in Alaska, Washington, Minnesota, and now Idaho. His work with KDL is sure to be a topic of considerable discussion at the next workshop for growers or other educational event Purvis attends. He is planning to have another Minnesota grafting workshop on March 24.

Agro-K reports that in the Midwest, strawberry growers often use overhead irrigation to form ice barriers to combat frost.  However, those without irrigation facilities or sufficient water use KDL directly on their fields with good results. Agro-K recommends using one gallon/acre about 24 hours before the expected frost event.

Agro-K notes that KDL is designed to enhance plant tolerance to frost, but is not designed to protect against severe or extended frost or freeze events. In any crop if temperatures are going to fall more than 5 to 7 degrees below freezing in the spring, growers with smaller operations will need to resort to sprayers or fans to drain away or recirculate cold air upward allowing warm air to drop into the vineyard or orchard if water protection is not an option. In the fall growers should keep in mind that ground temperatures will be warmer, meaning the air down low also can be warmer and protective, making fans counterproductive.

Large orchards and vineyards can activate the sprinkler systems or roll out the big fans to head off freeze damage. With this potassium nutrient any size growers can have a tool that can be deployed quickly, inexpensively and effectively if their crops are in for a cold bite as temperatures dip a few degrees below freezing for a short period.