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Oak Pests - A Guide to Major Insects, Diseases, Air Pollution and Chemical Injury

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Various abiotic stresses, insects, and pathogens

Importance. -- Oak decline affects mainly red oaks, over broad forest areas of the eastern United States. Damage varies by site condition, forest type, region, and year. Hickory species may also be affected when on sites with affected oak.

Identifying the Agents. -- Environmental, stand, and site factors usually are involved at first. Various insects and pathogens are involved in later stages.

Identifying the Injury. -- Oak decline usually affects mature overstory trees and is typified by a gradual but progressive dieback of the crown (figure 61), reduced growth, and tree death after several years.

Biology. -- Oak decline involves complex interactions between environmental and biological stresses and subsequent attacks by secondary pests. Predisposing factors, such as genetic potential, climatic factors, or old age, can set the stage for damage by some other injury. Drought, insect defoliation, unseasonable freezes, root damage, or extended flooding can incite active decline. Contributing factors, such as pathogens (e.g., Armillaria root rot, page 47), insects (e.g., twolined chestnut borer, page 20), or both, (figure 62) can kill trees.

Control. -- Harvest oak stands before they become overmature. Promote advanced reproduction in young and middle-aged stands to ensure regeneration at harvest. Removing dead and declining oaks to utilize trees before they degrade. (Note: none of these actions will correct conditions leading to decline.)


Figure 61
Figure 61. -- Red oak crowns in various stages of decline. From left to right: crowns are fairly healthy, actively declining, and recently killed.
Figure 62. -- Mycelial fans (white patches) of armillaria root rot and horizontal galleries (white lines) of two-lined chestnut borer at base of red oak in the last stage of decline.
Figure 62
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