White fluffy mould on an apple tree

Written by tracy hodge
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White fluffy mould on an apple tree
Powdery mildew causes a white fungal growth on apple trees. (Apple tree image by Olga Tkacheva from Fotolia.com)

Home gardeners often grow apple trees for the delicious sweet fruit they produce. Apple trees are also lovely specimen trees or can be used as a property border. Successfully growing apple trees requires proper care and maintenance. Apple trees are susceptible to a number of diseases, which can affect the health of the tree and the quality of fruit. Powdery mildew is common in apple trees and causes white fluffy mould to grow on the leaves of the tree.

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Identification

Foliage diseases can affect the health of apple trees. Powdery mildew is often seen in apple trees and is caused by fungi which overwinters in infected leaves and plant tissue. The fungi responsible for powdery mildew in apples is Podosphaera leucotricha. High humidity and temperatures ranging from 15.6 to 26.7 degrees Celsius (60 to 80 degrees Fahrenheit) are favourable conditions for powdery mildew development. This disease does not require moisture on tree leaves for infection to occur.

Effects

Apple trees infected with powdery mildew develop a white, fluffy fungal coating. This fungus resembles talcum powder, which is where the disease got its name. Powdery mildew fungus covers the leaves, fruit, flowers and shoots of apple trees. Infected tree leaves are soon entirely covered with white, fluffy fungus. Powdery mildew causes blossom buds to open late and affected leaves often become dry and brittle. Infected shoots produce unhealthy leaves that are covered with mildew at emergence.

Non-chemical control

Apple trees grown in the home orchard do not require chemical control methods unless powdery mildew infection is severe. Buying apple varieties that are resistant to powdery mildew is one way to prevent disease. Some resistant varieties include Priscilla, Jonafree and SirPrize.

Chemical control

Chemical controls may be necessary to control heavy powdery mildew infections. Spraying fungicides is an excellent means of control for powdery mildew. Begin spraying your apple trees when flower buds are tightly clustered and spray at regular intervals until terminal growth ceases.

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