Tree and Shrub Diseases: Phomopsis Blight, Anthracnose, and Black Knot

Three diseases that can really wreak havoc on many trees and shrubs include Phomopsis Blight, Anthracnose, and Black Knot.

Phomopsis Blight

Phomopsis Blight (Credit: Robert L. Anderson, USDA Forest Services)

Phomopsis Blight
(Credit: Robert L. Anderson, USDA Forest Services)

This disease is at its worst when new trees are wet. The disease commonly is a threat in the spring and causes growth to turn brown. If not treated and allowed to progress, the affected tree will die.

As the tree experiences continued damage, abnormal clustering and staining will occur on the leaves and stunting the growth of the young tree or shrub.

There are some things you can do to prevent the ailment. For example, you can make certain that your plants are located in full sunlight and in a well-drained area. Allow proper airflow and ventilation of the plants, so do not crowd. Prune diseased leaves to rid the plant of infection and to enhance airflow. Take time to disinfect the pruning shears in a one-part bleach to four parts water solution after each cut. If damage is severe, remove and destroy the affected plant. Water the plant’s roots in the morning to give it the rest of the day to dry, thus discouraging the formation of diseases including Phomopsis. You may also have to introduce a combination of cultural and chemical control. You can purchase fungicides that control Phomopsis at your local hardware store. Read the label before using the substance because it can damage some plants. Use according to instructions. Depending on the damage, you may have to apply the fungicide more than once to assure complete control.


Anthracnose (Credit: USDA Forest Service)

(Credit: USDA Forest Service)

The symptoms that identify this particular disease are brown, dry, blotchy spots that appear on leaves early in the season. In addition, the ailment could cause the leaves to fall off. At times Anthracnose is misdiagnosed as oak wilt.

This disease will spread to other trees during wet and cool conditions. Leaves may curl up along the veins and die.

Cut infected areas of the tree with pruning shears that have been disinfected with a solution of one part bleach to four parts water. Dip the pruning tool into the solution after each cut. When the growing season ends, carefully rake up and destroy all leaves that have fallen from infected trees. Space plants at a far enough distance to permit good air ventilation. You may be required to use cultural and chemical control. These products can be purchased from your local hardware store. These substances can damage other plants; so take caution as you use them. Read labels and instructions on use carefully before applying. You may discover you will need to apply the substance more than once in order to control the disease.

Do not prune oak trees between April and June or you could end up spreading the disease.

Black Knot

If you see a soft olive green growth that changes to hard black knots on the twigs of a tree in the fall, then it is possible the tree is infected with Black Knot. This illness usually threatens fruit and branches of the tree and it is lethal if not treated. The disease affects certain trees including Amur Cherry, Apricot, Black Cherry, Chokecherry, Dropmore Cherry, Flowering Almond, Flowering Plum, Japanese Plum, Korean Cherry, Mayday Tree, Mongolian Cherry, Nanking Cherry, Pin Cherry, Cultivated Plum, Wild Plum, Prunus Hybrids, Sand Cherry, and Sour Cherry. Once it takes hold it can claim an entire tree within a few years.

Cutting 4-inches away from the infection toward the trunk can help to prevent the disease from spreading. Use pruning shears that have been treated

Black Knot (Credit: Robert L. Anderson, USDA Forest Service)

Black Knot
(Credit: Robert L. Anderson, USDA Forest Service)

with a solution of one part bleach to four parts water after each cut. Take care to destroy the infected trimmings. If the tree is severely infected it may be best to remove it so it does not threaten other trees. You need to use a combination of cultural and chemical control. Use fungicide on the affected tree each spring to help fight the fungus that spreads the disease. You can buy fungicide the assist in controlling and even preventing black knot. The product can be found at your local hardware store.

About Robert Janis

Written by Robert Janis for LawnEq - Your specialists for Lawn Mower Parts and Small Engine Parts. We offer genuine premium OEM parts for Land Pride, Toro and many more dependable manufacturers.

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