By Terence Bradshaw
Pardon the exclamatory headline. I’m sending this message directly to the many, many people who have contacted me about the issue, and posting it as a blog post so that I can point to it when it comes up again.
Apple trees are dying all over the state. Maybe not necessarily dying, but they are looking very weak. I have had numerous calls and emails about trees with rampant leaf spots, small fruit, fruit drop, and, especially, early defoliation this year. Actually, I received quite a few last year as well. What’s up with apples in Vermont??
I have numerous photos in my inbox of trees that look like this- defoliating, often from bottom-up, leaves riddled with disease, some dead limbs, and no fruit. The most common thread among these trees is that they are all from unmanaged orchards. Backyard trees, wild trees, wildlife trees, these are generally not trees in managed, commercial orchards. So this message is not aimed at my usual commercial apple grower audience.
What we are seeing is the result of numerous environmental and biological stressors. Let’s go back to 2015. After a generally good ‘apple year’, when unmanaged trees bore relatively large crops of fruit statewide, nutrient reserves and cold hardiness going into the winter were compromised by the trees having to ripen an overabundant apple crop. The subsequent winter was normal but cold: a stretch of several nights saw weather in the minus teens below 0°F. The 2016 growing season was very dry. Both of those conditions are stressful on trees. Winter 2016-2017 was relatively mild, but the main stressor that in 2017 was the unrelenting rain in April, May, and June that resulted in rampant fungal infections, mainly of apple scab but also of cedar apple rust and other diseases. This caused major stress on unprotected trees, and although the weather turned dry by July, it shifted toward near-drought through fall, which further stressed trees. Coupled with a relatively large crop of scabby fruit which further weakened them, unmanaged apple trees were poorly-set to acclimate to a hard winter.
December 2017. Vermont apple trees were arguably as acclimated to cold winter temperatures as they were going to get, but that hardiness was questionable. I observed many trees that held onto their dry, desiccated leaves into the winter, which suggested that hardiness was marginal as the abscisic acid hormone that promotes hardiness and contributes to leaf drop didn’t have a chance to fully do its job. Then, cold weather came early (minus teens by December 15, and minus twenties by the holidays in many areas) and stayed for much of the winter, with some sites seeing -30°F or worse. That’s stressful on trees.
Finally, this spring (2018) was dry, and stayed dry through the summer for most of the state. All of the previous stressors, especially the wet spring / disease incidence of 2017; heavy cropload and dry fall; and early and intense cold led to trees that had a hard time in the drought of 2018, and many are calling it a day and dropping leaves early to rest.
Is this a major catastrophe? I wouldn’t say so- these trees have evolved functions to help them balance out their vegetative and fruiting growth to adapt to the extremes experienced in temperate regions. Will some of these trees die? Sure, but the majority will leaf out next year and keep going through their cycle. Are we going to see this again? Likely, especially as the climate gets more erratic and we continue to see greater swings in heat/ cold and rain/drought.
The best thing to do to reduce tree stress is to manage them. Prune them annually to balance out vegetative and fruiting wood and to encourage healthier 3-5 year-old wood in the canopy. Thin out the canopy to improve sunlight penetration, airflow, and to reduce disease incidence. Lime the soil if it needs it, add (judicious) amounts of fertilizer if the trees call for it. In those years when the tree is overladen with fruit, thin off 50-75% of them soon after petal drop when the fruitlets are nickel-sized to allow the tree to balance vegetative and fruiting functions. Water if it’s dry. If you’re ready to learn how to do it right and to commit to spraying, consider starting an Integrated Pest Management program for your trees. (That last step should only be undertaken after doing everything else).
Apple trees are not native to this region, despite their adaptability. More importantly, the apple as we know it was selected over millennia and is managed using the practices I mentioned to make it a regular-bearing, commercial crop. There is little about a ‘wild’ apple that suggests that, unmanaged, it will be ready to both provide quantities of high-quality fruit and survive this environment without management.
For more information, see the Cornell Guide to Growing Fruit at Home.
Good luck,
Terry
Where trade names or commercial products are used for identification,
no discrimination is intended and no endorsement is implied.
Always read the label before using any pesticide.
The label is the legal document for the product use.
Disregard any information in this message if it is in conflict with the
label.
The UVM Tree Fruit and Viticulture Program is supported by the
University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM
Grant, and USDA Risk Management Agency Funds.
