Jan 15, 2016Severe winters damage Michigan fruit trees
Two severe winters in a row – 2013-14 and 2014-15 – tested the resilience of Michigan’s tree fruit crops. The full extent of the long-term damage remains to be seen, but some lessons have been learned. Three Michigan State University (MSU) specialists shared those lessons during the recent Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, Michigan.
According to Bill Shane, Gregory Lang and Amy Irish-Brown, cold damage symptoms often appear as branch-end dieback and twig bark discoloration. Damage also can be seen as browning of the cambium, phloem and the newest xylem tissue layers under the bark.
The bark, cambium and phloem layers provide a protective shield around the inner core of the xylem (the heartwood). Cold damage reduces the ability of the outer layers to protect the heartwood from fungal and insect attack, and eventually the tree declines, according to the speakers.
Young fruit trees are particularly susceptible to damage, as well as older trees and trees in poor health, said Lang, an MSU professor of horticulture.
The 2014 winter was particularly hard on some mature apple orchards whose trunks and scaffolds were previously damaged by things like contact herbicides and mouse girdling, according to the speakers.
Shane, a district fruit educator with MSU, said that once you’ve assessed the level of damage to your trees, you have to decide if the planting is worth keeping. It’s a tough decision with a lot of factors to weigh, like the age of the planting, the value of the variety and current marketplace conditions.
But the earlier you make decisions and evaluate the damage done, not only from cold but from the potential introduction of disease organisms, the better off you’ll be in the long run, Lang said.
Lang used the devastating freezes of 2012 as an example. That spring, freeze events not only killed flowers but introduced bacterial canker in his cherry research plots. He lost a huge number of spurs on his young trees.
Lang didn’t prune his trees that spring of 2012, but said he should have. If he had pruned in spring instead of waiting until midsummer, his production the following year would have been much better.
In the winter of 2013-14 Lang saw a lot of damage on his apricot trees, much of it based on variety. He pruned the trees that were obviously damaged. The ones that looked healthy were full of canker, however, which wasn’t evident at first. During the following severe winter, a lot of those canker-infected trees collapsed and died. They couldn’t take two tough winters in a row.
Apples are probably the hardiest of tree fruits when it comes to facing winter cold, but signs of damage from fungal pathogens can be more subtle on apples than they are on cherries or peaches, said Irish-Brown, a tree fruit educator with MSU. If an apple tree is injured, you might not be able to tell right away.
“I suspect we’re going to see a slow decline in some of these blocks for another few years,” she said. “So be ready for that.”
If you see a damaged tree a year or two from now, it could very well have been injured in the winter of 2013-14 or 2014- 15, Irish-Brown said.
Recommendations
The speakers suggested that growers have an ongoing schedule of orchard removal and replacement, so their production comes from a range of
tree ages. Having a range of ages helps ensure that at least some portion of the orchards will survive.
Pruning practices have a huge impact on midwinter hardiness and recovery from winter damage.
If pruned from September to early January, trees – even supposedly tougher mature apple trees – are less winter hardy, as such pruning delays or reduces cold acclimation. Summer pruning also reduces the carbohydrate reserves of a tree going into winter, according to the speakers.
Severe pruning in the spring following a harsh winter can be tough on tree recovery. Growers may be tempted to prune hard to reduce tree height in no-crop years, but this might be a mistake if a tree’s health is poor, according to the speakers.
On cold-damaged trees that otherwise were healthy the previous season, corrective pruning in spring can remove mortally damaged branches. Early pruning of significantly damaged wood on such trees can provide more time and resources during the season for replacement growth, according to the speakers.
“Trees do have a memory,” Shane said. “They carry it in their wood and carry it in their growth structure for next year. It’s important for you to read the tree.”
— Matt Milkovich, Managing Editor
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