Winter Damage in a Chestnut Orchard

Our chestnut trees are important to us, we wish them no harm. When winter comes around and the chestnut trees are bare of leafs, we know the trees are at rest in a deep sleep. Even in a deep sleep, chestnut trees are living complex organisms, vulnerable to the elements. If harm comes to the trees, we likely will not see the symptoms of that harm until the following growing season.

The winter can inflect damage to chestnut trees with excessive cold, broker limbs from heavy loads of ice, and drowning in water saturated soils. Of these three issues, the broken limbs is observable when it happens. Not a pretty sight seeing broken limbs on the chestnut trees, but at least the damage does not lay hidden until the growing season is upon us. The broken limbs can be cleaned up during the winter so that when the growing season starts the orchard is clear of debris. If your orchard is located where chestnut blight is present, the open wood should be given a coating of wood sealer.

What is too cold for a chestnut tree? Too cold could be -35°F for some Chinese and European chestnut trees and their hybrids. Or -15°F might be to cold, depending on the cultivar. It also depends on when and how much nitrogen was applied to the chestnut trees during the past growing season. And then there is the old lady issue. “It’s to hot.” “It’s to cold.” “I can never seem to be comfortable in the place.” This is where the weather changes from well below freezing to well above freezing in just a few hours.

The winter of 2014/2015 caused a lot of winter dieback for many Michigan growers. Some orchards lost most of their Colossal trees to the severe cold. These orchards that lost their Colossals experienced -35°F or colder temperatures. We now know the cold limits of a lot of chestnut cultivars because of the 2014/2015 winter in MI. Some trees had dieback all the way to the ground. Some trees died completely, Some trees had dieback to the main branches allowing the tree to regenerate growth in the following growing season.

The winter of 2016/2017 in the Pacific Northwest brought a lot of winter dieback to some cultivars, but not all. The cultivars presenting some winter damage were Bouche de Betizac, Colossal, Prococe Migoule and Yooma. In picture #1 a Bouche de Betizac has cambium layer failure on the west side of the tree possibly due to the prevailing wind (Picture #1). At the 49th parallel, the sun remains very low in the sky and remains in the southern sky. So the damage is not likely sun scald. Picture #2 is a Yooma with new growth returning to a tree that looked like it had died completely.

The two winter events, 2014/2015 winter in MI, and the 2016/2017 winter in the Pacific Northwest helped isolate a few cultivars having very good cold tolerance. At the top of the cold tolerant list is Marigoule. Other cultivars showing similar cold tolerance to the Marigoule are Szego, Bisalta #2, Basalta #3, Eaton, Luvall’s Monster, Marrisard, Belle Epine, Regina and Regis Montis.

When chestnut trees experience significant damage from the environmental extremes, like extreme cold or excess water during the growing season, they become weakened to the point where they become susceptible to pests such as the shothole borer, aka ambrosia beetle. The shothole borer does not kill chestnut trees. The fungus the beetles carry and infect the trees with is what kills the tree. The range of the shothole borer is the entire lower 48 states of the USA. http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=530

Chestnut trees were found to have the signs of the ambrosia beetle (AB) entry into the chestnuts under stress. The most easily observable sign of the AB is small holes in the bark of the tree. Usually there is more than one hole in each tree. If the AB has entered a tree the tree will die if left without interventions. Once in the tree, insecticides are not effective to control the AB. ABs are active about the same time the chestnut trees come out of dormancy. In the picture above (Picture #3), the chestnut tree had AB entry wounds about 2 feet above the ground. To save the tree, the tree was cut off below the entry wounds. This tree has regrowth above the graft, retaining the value of the grafted tree. According to the insect scientists, the AB prefers stressed trees because the tree has a weakened infection response system.

In picture #1, the chestnut tree has suffered cambium failure of about 120 degrees on the trunk of the tree. This tree has a sucker growing from the base of the tree. The sucker would normally be removed during regular orchard maintenance. This sucker is being allowed to grow and to eventually replace the tree. The tree will eventually have a full failure of the tree in and around the area of the cambium failure, likely during a high wind event several years later. Consider using 90 degrees of failure to be the point of where a tree will be able to heal over the failure if it is blow the 90 degrees. If the failure is 90 degrees or more, the tree will have to be replaced or allowed to regenerate from suckers. If the suckers are below the graft union, then the tree will need to be regrafted.

The tree in picture #4 was about 6 years old. The tree budded out and formed leafs at the start of the growing season. Over the next 30 days the tree was observed in declining health. To try to save the tree the tree was cut back by about half its size. The tree continued to decline and all the leafs and branches died. The tree was left in place for the rest of the growing season. About 5 weeks after the tree was observed to have all dead branches suckers were observed emerging from the soils at the base of the tree. These suckers will be allowed to grow for the remainder of the growing season. The following spring one of the suckers will be selected for placement of a new graft. The other suckers will be cut off at the ground.