Peach tree diseases can be caused by fungus, bacteria or virus. Identification of diseases might be difficult because insect, rodent, bird, mechanical or hail damage can be confused with some diseases. Nutritional deficiencies and herbicide damage can also be mistaken for disease. In addition, disease symptoms may differ from season to season. Diseases tend to be spread by insects or have alternate hosts in other species.
Obtain new disease samples employing clean garden shears or a knife. Secondary organisms can invade diseased materials, making identification difficult or impossible.
Observe states surrounding the tree carefully. Start looking for additional diseased trees or alternate hosts such as chokecherry.
Look for decay or loose bark at the root/crown location. A moist, slimy canker and orange to brownish wood indicates phytophthora crown rot. It will have a definite margin to the decayed area. White, fan-like sequences of fungus under the bark and loose shoestring like strands on the surface of the bark indicate armillaria root rot. Big warty growths indicate crown gall.
Examine the branches. Limb dieback and the presence of amber gum indicate bacterial canker. This is differentiated from borer damage by the sour odor of the sap beneath the bark.
Inspect the twigs. Collapsed flowers and twig spurs, tan-centered cankers with dark margins on twigs and maybe gray-brown spore masses around the flowers and twig cankers suggest brown rot blossom and twig blight. The same organism can cause ripe fruit decay later in the season. Small purplish dark spots which expand to brownish spots with purplish margins on twigs and buds indicate shot hole disease. Tiny, dark brown bumps appear in the middle of each lesion. Fruit and leaf symptoms might seem that look like the twig lesions.
Look at leaves in many areas on the tree. Symptoms on one leaf are usually trivial, but many contaminated leaves on a tree demand attention. Thickened, curly new leaves that are yellow or red are indications of peach leaf curl. Leaves drop when disease is severe, and repeated severe illnesses may cause the decline of the tree. Infection occurs only on young plant tissue and can be spread by splashing water during rain or sprinkler irrigation. Aphids and herbicide damage can also cause peach leaves to curl. Powdery white fungal growth on the leaves and tips of branches is powdery mildew.
Assess fruit to get symptoms. Brown discoloration of the fruit early in its development, whilst flower parts are still attached, indicates jacket rot. The youthful fruit withers and falls in the tree within a couple weeks. The exact organisms can infect mature fruit, forming circular spots that spread rapidly over the fruit. This is called ripe fruit decay.
Scan for symptoms that occur on multiple parts or the tree or even to get general decline of the tree. Leaves that turn yellow on one or more branches or a single side of the tree indicate verticillium wilt. Because the illness progresses, the leaves drop off and the division will die. Blisters or sloping splits in the invading, bright yellow angular spots on the top surface of the leaves and brown spores on the lower surface and small brown spots with green halos on fruit indicate rust.