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Rhonda Ferree's ILRiverHort

Rhonda Ferree's Horticulture Blog

Evergreen Tree Problems Intensified by Drought


This summer's drought is tough on many landscape and garden plants. Unfortunately, plants already stressed by previous problems are in major jeopardy during this drought. According to Rhonda Ferree, extension educator in horticulture, the odd weather patterns in recent years has brought out many trees diseases. Spruce and pine trees are particularly at risk.

"Calls from landowners concerned about their dying windbreaks and from homeowners worried about their specimen evergreen tree are increasing in our Extension offices," says Ferree. Some are completely dead while others show partial needle browning and dieback.

Ferree says that identifying between spruce and pine trees is a good first step in diagnosing the problem. Spruce trees have small needles arranged along the stem. Pine trees have needles in bundles of two, three, or five along the stem.

Spruce trees were plagued by several different diseases in 2011, each with slightly different symptoms and treatment. The two most common diseases - Rhizosphaera needle cast and Cytospora canker - were confirmed by the University of Illinois Plant Clinic on spruce trees across Illinois.

Rhizosphaera causes older needles to turn a purple/brown color, while the newest growth appears green. Affected needles are cast (dropped). Since evergreens do not re-foliate along the branches, the disease will cause bare areas scattered throughout the tree.

Cytospora disease causes entire branches to turn purple/brown and affects all needles from the tip of the branch to the base. Often lower branches are affected first. The disease may progress up the tree slowly, killing branches over a number of years. The fungus is known as a stress pathogen, meaning it invades spruce trees growing in less than ideal sites or environmental conditions.

Pines are prone to several diseases as well, including diplodia blight, pine wilt, and Dothistroma blight. All three diseases will cause needles to turn brown. The pattern of symptoms will help with diagnosis in each case.

Ferree says the main pine disease in this area is diplodia on Austrian Pine. Diplodia tip blight causes entire needles to turn brown, not just tips of needles as might occur with Dothistroma blight, scorch, salt injury, or transplant shock. Diplodia blight causes all of the needles at the tip of a branch to turn brown.

Several practices can help reduce the amount of damage caused by these diseases. When the foliage is dry, remove dead branches and dead stem tips. Because the fungus survives on cones, rake and remove fallen cones throughout the season. Stressed trees are typically more susceptible to infection, so follow proper watering and fertilization to keep trees healthy. Chemical options are available for some diseases, but sprays this late in the season are not beneficial.

For Ferree, the most frustrating evergreen ailment occurs on white pine. "We usually refer to this situation as white pine decline, for want of an exact cause of tree death." "Often the complaint is sudden death, in as little as a month's time." "Other times the description is pale growth in the winter followed by death of the tree in the spring." Trees affected in the summer appear to die "almost overnight." The last situation is likely related to pine decline hastened by heat and drought stress. There are no cures for infected trees. Try providing water in periods of drought, fertilizing with an acidic fertilizer, and waiting to see whether the tree will respond.

For more information on these diseases and more, read the Home, Yard, and Garden Newsletter from University of Illinois Extension at http://hyg.ipm.illinois.edu/index.php. You can also post questions on Rhonda's facebook page at www.facebook.com/ferree.horticulture.



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