Invasive Species, Disease, Pests and unwanted plant growth
What should I do if I think my tree has insect and/or disease problems?
As soon as you notice any abnormality in your tree’s appearance, you should begin a careful examination of the problem. Insects and diseases can threaten a tree’s health. By identifying the specific symptoms of damage and understanding the causes, you may be able to diagnose the problem and take appropriate actions for treatment. You should contact a tree care professional for assistance immediately.
Common Infectious Diseases and Pests
in the Twin Cities and Surrounding Areas
Dutch Elm Disease: A fungal infection spread by three species of Elm Bark Beetles. The first symptom of infection is usually an upper branch of the tree with leaves starting to wither and yellow in summer, months before the normal leaf shedding. This progressively spreads to the rest of the tree, with further dieback of branches. Eventually, the roots die, starved of nutrients from the leaves. Often, not all the roots die; notably the English elm puts up suckers which flourish for many years, after which they also die.
Emerald Ash Borer: The emerald ash borer is now one of the most destructive non-native insects in the United States. It has killed at least 50 to 100 million ash trees so far and threatens to kill most of the 7.5 billion ash trees throughout North America. One sign that the emerald ash borer has infested a tree are D-shaped holes in the bark of the trunk or branches. The Minnesota Department of Agriculture has strict guidelines for the detection of the pest and destruction of affected trees.
Bronze Birch Borer: Similar to the EAB, the Birch Borer larvae tunnel underneath the bark and are white, segmented, legless grubs with an enlarged area behind the head. All birch species can become infested. Symptoms of Birch Borer infestation include midsummer yellowing of foliage on some branches in the canopy, progressing to brown/dead leaves. This results in the death of smaller branches in the upper crown.
Birch Leafminer: Birch leafminers are among the most common insects affecting landscape trees and shrubs in Minnesota. They feed inside the leaves of gray, paper, river, and European white birches, forming blotch mines, (partial or whole areas inside the leaves are consumed).
Scale: Scales are insects that feed by sucking plant sap and may cause poor, stunted growth. Death of infested plants is possible in severe cases. A large quantity of sweet sticky liquid called honeydew is excreted by scale insects. Honeydew can make a sticky, shiny mess on the plant and nearby furniture and floors. Large amounts of honeydew can foster the growth of black sooty mold.
Common scales found in the Minneapolis area include:
Pine Needle Scale which are white, oval-elongate, 2.5-3 mm long and affect pines, spruces, firs, and hemlock.
Spruce Bud Scale which appear round, reddish-brown, and often in clusters of three to eight individuals. They closely resemble the buds of their host: spruces, particularly Norway spruce.
Cottony Maple Scale is conspicuously identified as a brown adult female with a large cottony mass (egg sack) protruding from the rear. Commonly affected trees include maples (especially silver), honey locust, linden and other hardwoods.
Apple Scale may be from 1/20 to 1/4 inch in diameter and are usually found on the stems and/or leaves, but in some cases they also present on the fruit.
Insect Gall: Galls are irregular plant growths stimulated by a reaction between plant hormones and a powerful growth regulating chemical produced by a feeding insect, commonly aphids, mites, wasps, and flies. Galls can occur on leaves, bark, flowers, buds, acorns, or roots.
Apple Scab: Apple Scab is a fungal infection that affects both apple and crabapple trees. It most often appears as dull black or grey-brown lesions on the surface of tree leaves, buds or fruit. The fungus reproduces in the leaf litter at the base of the tree through the winter, moving up into the tree in the spring as the tree comes out of dormancy. Applying a fungicide can help combat this non-fatal malady.
Oak Wilt: Oak Wilt is a fungal infection that is most common in the Upper Midwest. The leaves at the crown of the tree will begin to wilt first, migrating down as the flow of nutrients from the roots ceases to reach the upper parts of the tree. Complete wilting of a mature oak can occur in as little as two months.
Environmental causes for tree decline:
Environmental factors contribute to tree decline in many ways, including leaving a tree more susceptible to infection from pathogens or infestation from invasive species.
Compacted Soil around the root system,
such as under paved driveways, sidewalks, etc.
Insufficient or Over-watering
Root Girdling, which is a condition wherein one root has grown around the base of a tree, basically choking itself to death.