- Peach trees will not tolerate heavy, extended freezes. They are grown in warm southern climates. Warm, humid growing conditions can make them susceptible to a number of warm-weather diseases. Some newer cultivars for home gardens have been developed with cold-hardiness in mind, but they are generally not suitable for northern-orchard growing because late frosts are still likely to nip buds and prevent fruit formation. Even if the trees survive, an entire year's fruit crop may easily be lost.
- Most peach tree diseases are caused by fungi. Several problems caused by mites and other insects masquerade as diseases. And insects can also spread diseases. To find out exactly what is wrong with a tree, check with a local county horticultural agent. It is important to know whether to treat for a fungus or an insect.
- Fungal diseases are more prevalent in the humid areas of the southeastern U.S., and not as common in the more arid west. Orchard sanitation is an important step in the prevention of disease. Prunings, tree debris and old fruit should be kept cleared away. Mowing should be well-maintained to discourage insect populations as well as competition for nutrients.
- Peach leaf curl appears as rusty spots on the leaves that blister and curl in a deformed way. This is a fungus disease that is due to cold, wet weather in the spring. It is treated with copper hydroxide in a spray form. It is usually considered organic, but specific brands may not be certified as such.
Brown rot is a widespread fungal disease that plagues peach growers. It occurs at all stages of development. Commercial growers use chemical sprays, and organic growers use sulphur applied in weekly intervals.
Powdery mildew is a fungus caused by Sphaerotheca pannosa. It overwinters in debris, so keep the area around trees raked clean and get rid of old fruit.
Peach tree borers are destructive wasp-like insects that lay eggs near peach trees. The larvae burrow into the tree trunk above and below ground level, leaving a tell-tale oozing in the bark. A fungus disease, cytospora canker, is easily confused with peach tree borers because it also causes the oozing. Make a careful diagnosis before treating.
Plum curculio and coddling moth larvae infest fruits, and are difficult to control without chemical sprays. - Most commercial growers use chemicals to treat fungal diseases and insects.
Organic controls can be effective, but they must be applied at the correct time to prevent damage. If organic methods are to be used, keep a careful watch for tree bud development, and apply dormant oil spray at appropriate intervals. Beneficial soil nematodes are effective against soil-dwelling larvae. Nematodes are living microscopic worms that must be applied with plenty of water and when the soil temperature is more than 50 degrees at a depth of 4 inches. They feed on many species of grubs or larval-stage insects.
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