Are the leaves on your apple tree turning yellow and falling off? Check the leaves and see if they are full of small brown spots. The yellowing and spotting of apple leaves is caused by a fungus disease called Black Rot. The disease is also referred to as "frogeye leaf spot" due to the appearance of the leaf spots.

The black rot fungus over winters in cankers and dead wood. In the spring, spores are formed on the cankers. During rainy periods, the spores are secreted from the cankers and spread by splashing raindrops to the fruit, leaves, and branches where infection occurs if conditions are right.

Leaf spots appear first as small purplish brown specks, then enlarge to about 1/8 to 1/4 inches in diameter. Older spots have irregular purple-brown margins and centers with alternate bands of light and dark giving the spots a frogeye appearance. If the number of leaves yellowing and falling off is severe, the tree may put out new healthy leaves. Infected fruits develop a hard brown to black rot which continues to expand until the entire fruit is rotted.

Sanitation is the primary means of controlling Black Rot. Remove all dead and infected branches from your trees, clean up and treat all sunscald cankers, pick up all fallen apples in the fall, and applying pruning paint to all wounds. Chemical controls won't help much since the fungicides available will prevent the disease from infecting the leaves, but won't stop its progress once the infection has occurred.

This page was last updated May 2003

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