Problem Identifier Unit Screen//v.w/ RR Template

Problem Identifier Unit Screen//v.w/ RR Template Root and Crown Rots

Problem
The normal leaf color dulls, and the plant loses vigor. Leaves may wilt, or turn yellow or light brown. Major branches or the entire tree may die. The tree sometimes lives for many months in a weakened condition, or it may die quickly. Fruit growing only on the upper branches is a common sign of a tree's decline. The roots and cambium (thin layer of tissue just beneath the bark) of the lower trunk are brownish, and the roots may be decayed. In the Southwest only, fine woolly brown strands may form on the roots, and white powdery spores on the soil surface. Or fan-shaped plaques of white strands may appear between the bark and wood of the roots and lower stems. Mushrooms may appear at the base of the plant in the fall.

Analysis
Root and crown rots are caused by any of several different fungi that live in the soil and on roots. They are spread by water, soil, and transplants.

1. Phytophthora species: These fungi cause browning and decay of the roots and browning of the cambium and wood of the lower trunk. The tree usually dies slowly, but young trees may wilt and die rapidly. The disease is most prevalent in heavy, waterlogged soil.

2. Phymatotrichum omnivorum: This fungus, commonly known as cotton root rot or Texas root rot, is a serious problem on many plants in the Southwest. Young trees may suddenly wilt and die. Brown strands form on the roots, and white powdery spores form on the soil. The disease is most severe in heavy, alkaline soils. (For more information about cotton root rot, see Cotton Root Rot, Armillaria Root Rot.)

3. Armillaria mellea: This disease is commonly known as shoestring root rot, mushroom root rot, or oak root fungus. It is identified by the presence of fan-shaped plaques of white fungal strands between the bark and the wood of the roots and lower trunk. Honey-colored mushrooms may appear at the base of the plant. (For more information, see Cotton Root Rot, Armillaria Root Rot.)

Solution
The numbered solutions below correspond to the numbers in the analysis.

1. Remove dead and dying trees. When replanting, use plants that are resistant to Phytophthora. (For a list, see Plants Susceptible and Resistant to Phytophthora.) Improve soil drainage. (For more information, see Soil Types, Soil Structure, Groundwater.) Avoid overwatering plants. (For more information, see About Watering.)

2. Remove dead and dying trees. When replanting, use only resistant varieties. (For a list, see Plants Resistant to Cotton Root Rot.) Before planting, increase the soil acidity by adding 1 pound of ammonium sulfate for every 10 square feet of soil. Make a circular ridge around the planting area, and fill the basin with 4 inches of water. Repeat the treatment in 5 to 10 days. Improve soil drainage (see Soil Types, Soil Structure, Groundwater).

3. Remove dead trees and as much of the root system as possible. If plant is newly infected, expose the base of the plant to air for several months by removing 3 to 4 inches of soil. Prune off diseased roots. Use a fertilizer to stimulate growth. (For more information, see Nitrogen and How to Read a Fertilizer Label.) When replanting, use only resistant plants (see Plants Resistant to Armillaria Root Rot).

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