Pests and diseases

The trees are susceptible to a number of fungal and bacterial diseases and insect pests. Nearly all commercial orchards pursue an aggressive program of chemical sprays to maintain high fruit quality, tree health, and high yields. A trend in orchard management is the use of Integrated Pest Management (IPM), which reduces needless spraying when pests are not present, or more likely, are being controlled by natural predators.

Spraying for insect pests must never be done during flowering because it kills pollinators. Nor should bee-attractive plants be allowed to establish in the orchard floor if insecticides are used. White clover is a component of many grass seed mixes, and many bees are poisoned by insecticides while visiting the flowers on the orchard floor.

Among the most serious disease problems are fireblight, a bacterial disease; and Gymnosporangium rust, apple scab, and black spot, three fungal diseases.

The plum curculio is the most serious insect pest. Others include Apple maggot and codling moth. For other Lepidoptera larvae which feed on apple trees, see List of Lepidoptera which feed on Malus.

Young apple trees are also prone to mammal pests like mice and deer, which feed on the soft bark of the trees, especially in winter. Growers usually sheath juvenile trees with wire mesh to protect them.

Apples are difficult to grow organically, though a few orchards have done so with commercial success, using disease-resistant cultivars and the very best cultural controls. The latest tool in the organic repertoire is to spray a light coating of kaolin clay, which forms a physical barrier to some pests, and also helps prevent apple sun scald.