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Managing Hail Damaged Trees

Photo Source: Clemson Extension

Maureen Sexsmith-West ISA Certified Arborist, PR4600A

Extreme weather has really taken a toll on Albertan’s this year. Like many of you, I have given up on the possibility of having fresh cucumbers from my garden this year. Trees and shrubs are more costly than perennial plants so they should be your first priority after a storm.

How will trees survive the flooding and hail damage. Time and patience is the best answer. Hail damage is the result of intense impact. It crushes the tissues which affects the trees ability to move water and nutrients in a continuous straight line along the vascular tissues from roots to secondary limbs and twigs and the leaves. Hailstones rip and shred leaves, and defoliate branches on the windward side of the tree. Depending upon the size of the hail, it can tear bark on young and thin-barked trees (Birch, Mountain Ash, Linden, etc.) on both the upper surface of smaller secondary branches and the side of the main trunk facing the storm, and damage the underlying vascular tissues. Smaller twigs can become torn away. Wounds are often a key infection sites for diseases. Some varieties that are ‘self shedding’ like willow will easily break off. While hail can destroy leaves, some deciduous trees may have enough reserve to re-leaf in the same growing season. This takes a lot of energy and can put the tree into a deficit and vulnerable to secondary issues such as insects and diseases. The bark tissue around these injury sites dies. Physical damage to tree bark is usually easy to see on smaller trees following the storm. Mature trees with hail damage may show symptoms later as drying of the dead tissue and formation of callus tissue causes the bark to crack. This type of injury is often found on golf course trees where they are frequently struck by golf balls. Over the next few years, trees will produce callus tissue to seal off bark wounds and re-establish vascular function. Until then, they have a reduced ability to cope with dry conditions, which are often compounded by high winds that dehydrate leaves more quickly. Evergreen trees hold their needles for several years. This makes defoliation much more serious on evergreen trees than on deciduous shade trees. Evergreen trees may show severe thinning of the needles on the side of the tree that faced the storm. If a majority of the branches are still alive and put out new growth this spring, the tree has a good chance to survive and eventually fill in on the damaged side. Here are some guidelines to help your trees recover from hail damage:

  1. Prune off any broken branches. Damaged limbs that will not heal quickly should be pruned off cleanly. If trees or shrubs were split and large limbs broken, create a clean cut but DO NOT APPLY PRUNING PASTES. Use proper pruning cuts, taking care not to cut into the branch bark ridge.

  2. Inspect branch wounds and monitor throughout the growing season. Many will callous over the proper watering and maintenance.

  3. Turf irrigation systems apply water more shallowly than trees need. Don’t rely on automatic systems to meet the needs of your trees.

  4. Keep trees well watered throughout the summer by a deep soaking once per week (1 inch of water applied over the entire root zone). Adjust in response to natural rainfall.

  5. DO NOT FERTILIZE YOUR TREES THIS LATE IN THE SEASON. A fall application may be appropriate but in most cases, products of this type are only available to commercial tree care providers.

  6. Protect your trees from additional stresses. Inspect your tree more often and address insect infestations and prune out diseased plant material.

Photo Source: Clemson Extension

  1. Thin out and remove hail damaged fruit.

Wait to make a final evaluation of trees until the next growing season.

Watch this Video for great information from Susan Browning. Please note that some of the diseases references may not be typical in our region.

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