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Drought Stress: Your Trees Are More Susceptible to Pests & Disease!

By Micah Pace
ISA Certified Arborist TX-3752
Professional Urban Forester
Qualified Tree Risk Assessor

Trees are constantly under a variety of environmental stresses. The stress factors imposed on them range from chemical (nutrient deficiencies) to mechanical (storm damage and construction damage) to cultural (misuse of pesticides/fertilizers, poor pruning practices, over watering and poor planting practices). Under normal conditions, trees are fairly well equipped to handle these stresses and in most can cases recover. However, during prolonged drought conditions a tree’s resources are often exhausted trying to withstand the lack of available water.

While pest and disease are a continual part of a tree's natural life cycle, trees are much more susceptible to damage when drought stressed. As we move closer and closer into the heat of another tough Texas summer, an increase in pest and disease problems are to be expected. One disease in particular that should be expected to become a bigger problem through the hot dry summer is Seiridium canker disease. 

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Seiridium canker disease is caused by Seiridium unicorne, and in the DFW area it most commonly affects Leyland and Italian cypress trees. Plants of all sizes and ages are affected. Cankers may form on stems, branches and in branch axils causing twig, branch or stem dieback. Cankers appear as sunken, dark brown or purplish patches on the bark, often accompanied by extensive resin flow. However, resin flow often occurs from the branches and stems of otherwise healthy plants of Leyland cypress, so resin flow by itself may not be confirmation of a Seiridium canker.

Scattered twigs or branches killed by the fungus turn bright reddish brown and are in striking contrast to the dark green healthy foliage. Fruiting bodies of the fungus appear on the bark surface of the cankers as small circular black dots barely visible to the naked eye. Spores of the fungus are spread to other parts of an infected tree, or from tree to tree by water splash from rain or irrigation. The fungus can also be spread from tree to tree on pruning tools. Long distance spread appears to be through the transport of infected cuttings or plants.

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While pest and disease problems cannot be avoided completely, maintaining cultural practices in the landscape is a great first step to avoiding heightened susceptibility of infection. Overwatering Leyland and Italian cypress trees will increase the risk of infection. 

Concerned about your trees? Only an experienced arborists can examine your trees and provide you with science based treatment recommendations.



Entry Info

Categories: Trees, Disease
Tags: Disease, Preservation, Trees
Posted: June 12, 2014