- The twig borer or the Oriental fruit moth is a small brown moth at maturity. As a caterpillar, it forms a cocoon to winter in. When leaf buds begin to emerge on the peach tree in the spring, the caterpillars emerge and feast on the new growth at the tips of the limbs. As soon as the buds break and the peach tree shows color, spray with a dormant oil, a highly refined petroleum oil. The oil coats the limbs, the cocoons and emerging caterpillars, suffocating them. If the tree is not treated in the spring and the tips of the limbs begin to droop, prune off the tips and pick the caterpillars off manually. When fruit emerges, any remaining caterpillars will bore into the fruit. An insecticide containing diazinon and methoxychlor applied in June is effective against this pest.
- The greater peach tree borer is a clear-winged moth that can girdle or kill trees. It can be identified by its blue body with yellow stripes. The moths lay eggs near the base of the tree around July, depending upon the part of the country you live in. The larvae bore under the bark, leaving sapping holes or sawdust in or under the holes. Endosulfan should be applied to the lower trunk to kill the eggs and larvae. This should be applied in early July and again 30 days later. Once the borers have infested the tree, mechanical means must be employed. Insert a wire into each hole and puncture the insect.
- Brown rot is a fungus that is particularly damaging in warm, humid environments. It affects the blossoms and fruit of the peach tree through the growing season. Blossom blight during the blooming phase indicates a considerable infestation. Planting in a well-ventilated area and pruning the tree helps, because increasing the air flow allows the branches to dry more quickly. Pruning may be done in July, as well as during the dormant season, and all debris should be cleaned up and discarded.
Excessive nitrogen in fertilizer can increase the occurrence of brown rot. Sulphur is traditionally used to control this fungus. The first application should be done when the tree buds, but before the blossoms open. Repeat the application every seven days until three applications have been made. Spray again when the petals drop and again 7 to 14 days after that when the sepals drop. - Peach leaf curl is another fungal problem. Wet springs can cause the leaves to deform and fall and generate new leaf growth, which stresses the tree and reduces fruit production. Once the leaves emerge, it is too late to treat the tree. Spraying with lime sulphur during the tree's dormant period is the only way to combat the problem. A good time is March or May, before the tree begins to bud. An application in the fall, after all the leaves, may be beneficial, too.
- Bacterial spot, bacterial canker and peach scab can overwinter in trees. Treat these with copper spray while the tree is dormant. It can be blended with dormant oil used to treat insect infestations while they are overwintering, so that only one application need be made. Do not mix copper sprays with lime sulphur, however.
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