Major Diseases of Peach in Georgia
Brown Rot (fungus Monilinia fructicola)
Infection may occur on blossoms causing a rapid withering and browning. Twig infection may occur resulting in gumming and cankers. Occasionally, small branches and twigs will be girdled and killed by brown rot canker. The most common and destructive phase of brown rot is fruit rot. The rot begins as a small brown spot which expands rapidly, developing a brown color and a more or less firm texture. The fruit becomes more susceptible as it matures. Brown rot is especially severe during wet periods. Infected blossoms, twigs and fruits soon become covered with gray-brown tuffs of spores. The brown rot fungus overwinters on mummified fruit on the ground or tree and in infected twigs.
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Scab (fungus Cladosporium carpophilum)
Peach scab occurs on leaves, twigs and fruit causing small, circular to oval-shaped spots. The infected areas are dark brown to black in color and entirely superficial. On red skinned or blushed varieties, fruit spots may be surrounded by a light-colored halo. Economic damage is mainly due to loss of fruit appearance quality, although heavily infected fruit may become misshaped or cracked. Initial fruit infection occurs during the first four weeks after shuck fall. The disease overwinters on twig lesions. The fruit symptoms may be confused with those of bacterial spot.
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Bacterial Spot (bacterium Xanthomonas pruni)
Bacterial spot occurs on leaves, twigs and fruit. The leaf symptoms begin as a deep purple to brown spot surrounded by a pale green halo. As the leaf expands, the infected spots separate and drop out leaving a ragged or shot-hole appearance. Many infected leaves turn yellow and drop resulting in premature defoliation. Twig infections appear as darkened areas with water soaked margins and may cause twig die-back. Fruit symptoms are small, circular purple-brown spots often with a light center and/or a water soaked margin. Heavily infected fruit may crack open and occasionally show gumming. Varieties vary widely in susceptibility to bacterial spot. The fruit symptoms may be confused with those of peach scab.
Rhizopus Rot (fungus Rhizopus nigracans)
Injuries in fully matured fruit act as infection sites for Rhizopus rot. The disease develops very rapidly in warm temperatures. Infected tissues become very soft and watery. The surface of infected fruit soon becomes covered with coarse, fungal growth and black spore producing structures. The disease spreads rapidly to adjacent fruit at the point of contact. This disease can become very severe when wet weather at harvest is combined with careless fruit handling.
Nematodes (root-knot Meloidogyne spp.)
Root-knot nematode symptoms occur as small, spherical galls or knots on the roots of peach trees. Trees infected when very young may die from massive root destruction. Older trees that gradually become infected, generally do not die but become weaker as more of the root system becomes damaged. Infected trees often show a lack of vigor and may show wilt symptoms during dry periods. Nursery stock showing any sign of root-knot nematode should not be planted. Lovell root stock, the recommended peach root stock for most of Georgia, has no resistance to root-knot nematode. Nemagard root stock, which is generally not recommended for Georgia, shows resistance to M. incognita and M. javanica but has no resistance to M. hapla or M. arenaria. All efforts to control root-knot nematode should be made prior to planting an orchard.
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Crown Gall (bacterium Agrobacteriurn tumefaciens)
Crown gall occurs as tumorous rough surface growths on roots and crowns of trees. Galls can be verb smallto more than a foot in diameter. The bacteria enter the tree through fresh wounds. Crown gall can be a veryserious problem for nurserymen. Trees infected when very young may soon die. Older trees may become weaker, but generally do not die from crown gall. Once land has become infested with the bacterium by introduction of contaminated plants or soil, it must be regarded as permanently infested. Infected nursery stock should never be planted. Very small crown galls can be confused with galls caused by root-knot nematode. Crown gall, unlike root-knot nematode, seldom shows profuse development in the feeder root system.
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