How to Stop Fungus on Fruit Trees Naturally

Wet the leaves to stop sooty mold. The black substance appears on the surface of leaves, growing on the honeydew deposited by insects. Direct a hose or sprayer over the foliage in the morning to reduce honeydew. Avoid spraying in the evening because wet foliage and cooler nighttime temperatures will encourage the sooty mold to spread.

Prune branches affected by verticillium wilt, a fungus that causes light-colored leaves to look dull and drop prematurely. Trim off branches where they meet healthy wood. Water and fertilize the citrus tree with a nitrogen-rich food to promote new foliage growth. You can tell the fertilizer is high in nitrogen if the first number on the label is higher than the others, such as 15-1-1. The first number depicts the percentage by weight of nitrogen.

Cut off all developing knots to reduce black knot, a disease causing abnormal growths on smaller branches of plum, chokecherry and sour cherry trees. These growths look like dark green or black elongated knots. Prune 4 to 5 inches below each knot during dormancy to remove the disease. Dip the pruning shears in disinfectant or a mixture of six parts water to one part rubbing alcohol between each cut. Bury, burn or throw away the removed material to prevent spread. Monitor the tree for new black knots during the season.

Reduce bacterial spot with a balanced fertilizer. Bacterial spot shows itself with irregularly-shaped spots on the tree leaves and dark brown to black spots on the fruit. Because an excess of nitrogen will encourage disease, use a fertilizer with a nitrogen-phosphorus-potassium ratio similar to 15-30-15. Keep young trees away from old trees because the young trees are susceptible to this disease.