Cold spell concerns fruit growers, but little can be done

SALEM, Ohio — The unusual cold spell that plagued Ohio and Pennsylvania the second week of January has fruit growers concerned about long-term damage. Ohio saw temperatures of minus 10 and lower — the lowest since 1994.The full extent of the damage could be weeks to months away, but there are already some things to watch for.

Two Purdue University experts in the department of Horticulture and Landscape Architecture produced a report of some of the biggest concerns for the affected states.

Snow cover

Places that had good snow cover prior to the cold temperatures were fortunate, the authors said, because the snow helped protect roots from damage.Trying to predict the amount of bud, tree and vine damage is complicated because there are many factors including minimum temperatures, duration of cold temperatures, acclimation and the previous season’s crop load.

The temperature across much of the Midwest has been as low as minus 15 or so. Damages depend on the type of fruit, and local conditions.

Apples and pears

Both are very hardy, but temperatures were close to where producers could start to see some bud damage. It seems unlikely that bud damage will be severe enough to reduce crops.

Peaches and nectarines

The rule of thumb is that you start to see some flower bud kill at minus 10 and for every degree below minus 10 you lose 10 percent of your flower buds. At minus 20, expect complete flower bud mortality. Expect to have some early thinning occurring, but crop reduction shouldn’t be too severe.

Sweet and tart cherries

Tart cherries are a little more hardy than sweets, but growers could see a little bud damage to both sweets and tarts, but at current temperatures. This is unlikely to limit 2014 crops.

Blueberries

Highbush blueberries are generally tolerant of temperatures down to minus 15, but the extended period of cold will likely lead to some flower bud kill.

Blackberries

Thorny and thornless blackberries are not hardy below minus 10, so experts expect to see considerable damage to vascular tissue in canes and potentially buds themselves. In severe cases, expect all above ground growth to be killed.

Blackberries commonly exhibit a delayed winter injury response, where the buds may have survived the winter cold and begin to grow in the spring, but the damage to the vascular tissue in the canes results in collapse of the new growth a few days or weeks after the start of growth.

Raspberries

Red and black raspberries are fairly cold hardy and producers should expect minimal damage to varieties that are adapted to the Midwest. Some red raspberry varieties from the Pacific Northwest are not very cold hardy and may have been damaged.

Grapes

Varieties will vary widely in amount of damage. Grapes have a compound bud, with primary, secondary and tertiary growing points. The primaries are usually the first to show cold damage. Expect hardy hybrid and American varieties to have 0 to 25 percent primary bud damage at the temperatures the Midwest experienced.

That is manageable, as producers can adjust pruning severity to account for those losses. Less hardy hybrids may have 50 percent or more bud damage, which could lead to some yield reduction and potentially cane and cordon damage. Cold tender vinifera varieties likely have experienced considerable damage to buds, canes, and cordons and possible damage to trunks above the snow line.

The Ohio Wine Producers Association says a greater fear is if frigid temperatures remain or return in the winter for an extended time. Then, actual vine damage (or even death) will occur.

In January of 1994, when temperatures remained significantly below zero for 14 days, many vineyards faced major replanting schedules, along with the loss of three or more years of production until the new vines were ready to harvest.

Making improvements

Since then, growers have become more selective about the sites where their most tender varieties are planted. They have added every-row tiling to drain excessive water, which was identified as a culprit during those two frozen weeks, and added wind machines which, on a still night can mix the layers of air and raise vineyard floor temperatures several degrees.

Grape growers are encouraged to delay any additional pruning for a while, to leave as many buds as possible, to wait until the cold snap passes and to do random bud cuts to check for dead tissue, to assess pruning plans.