May 17, 2016
Hard freeze hit fruit orchards in April

Imagine a winter rather like this past one. A winter where February behaved like March (mostly) and March impersonated April. A delight to be sure. But not for the fruit grower with an eye on the weather. Not in New York; not anywhere in the Northeast or parts of the upper Midwest, for that matter. If growers made it through that sudden plunge on Valentines Day (which wiped out the peach crop in the upper Hudson Valley and several other northeastern states), it was time to start worrying all over again. Because along came April — an ordinary April. An April with nighttime temps that dropped like a stone in a well.

"Old temp" is the lowest temperature blossoms can endure, undamaged, for 30 minutes.
“Old temp” is the lowest temperature blossoms can endure, undamaged, for 30 minutes. Photos: Cornell

Whether they grow apples or pears, cherries or blueberries, growers might (even now) have reason to worry. They’ll likely get a decent crop this year if their orchards are sited on slopes with good air drainage, just-right soils that help slow bud-break, and the moderating influence of nearby lakes or oceanfront. And then there’s the simple fact that, for apples and pears (peaches too) at least, one viable blossom per cluster is about all a tree needs for a good crop. The trees might lose 90 percent of their blossoms, but growers don’t have to go back and thin them when the trees set fruit — Mother Nature just did it for them. (This rule of thumb doesn’t work for cherry or blueberry growers, though what mix of varieties they grow can make a big difference at harvest time.)

Growers in the most vulnerable locations did any or all of these four things:

  • Checked their Extension specialists’s email posts for advice.
  • Stocked up on fuel for smudge pot or burn piles.
  • Prayed for a temperature inversion.
  • Put up wind towers or called their helicopter pilot.

The Extension specialist (in this case Peter Jentsch, senior Extension associate at Cornell’s Hudson Valley Research Lab) probably said that smudge pots or small, strategically placed fires — 40 to 60 per acre — could help, raising ground temperature just enough to squeak by. “Strategically” means on the upwind side of the block. “Squeak by” means raising ground temps by about 3°. If 3° won’t do it, he would’ve said, don’t bother. And minus a temperature inversion — a canopy of slightly warmish air blanketing the cold air below it — don’t set up the wind machine or call the helicopter pilot. All it would do is blow more frigid air around, drying out buds and growing tips.

Smudge pots, strategically placed, raise temperatures just enough to make a difference.
Smudge pots, strategically placed, raise temperatures just enough to make a difference.

If there’s an inversion, those heaters and small fires might also have helped. Note that Jentsch didn’t say “bonfire.” Too hot a blaze could punch through to the inversion layer, depleting it. And growers who work on a big-enough scale might have turned on their wind machines or called an experienced pilot, because when it’s not too windy it could be worth a trip to the skies. The premise: a helicopter hovering overhead pulls down that warmish air. The ‘copter’s thermometer tells where and how the temperature shifts as it gains altitude. Depending on how much it shifts and how thick the canopy is, the decision is — is it worth paying big bucks to mix up?

April is past; May has begun. Jentsch is in touch with growers and other Extension specialists all through the Hudson Valley and beyond. “It’s not all the doom and gloom,” he says. “Growers with the best sites and mix of crops seem to be doing all right.” Still, it’s sobering to think about the effect two days at the wrong time can have, Jentsch says. “For the growers who got hammered, it can throw a their livelihood into a tailspin for many months to come.”

So there you have it — an April rather like this one. Normal in every way but one — that it followed so mild a winter.

Mary Woodsen, Cornell University

Source: New York State Integrated Pest Management Program


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