Major diseases of Plum are:-
1.Bacterial Canker: Pseudomonas syringae
- Cankers develop at the base of infected buds on trunk and scaffold limbs. Cankers spread more rapidly above the point of infection than below and only slightly to the sides.
- This results in a long, narrow canker. Cankers develop during the fall and winter but are not visible until late winter and early spring.
- Damaged areas are slightly sunken and somewhat darker in colour than surrounding bark. As the trees break dormancy in the spring, gum is formed and flows down the outside of the tree.
- Cankers have a soured smell. The bacterium is a weak pathogen and causes serious damage only when a tree is in a near dormant condition or weakened due to unfavourable growing conditions.
- Avoid using high fertilizer rates in late summer. Succulent, late fall growth is more easily infected. Prune when trees are fully dormant (January and February).
- Trees showing signs of bacterial canker should be left and pruned after all other trees have been completed.
2.Brown Rot: Monilinia fructicola
- The brown rot fungus can cause blossom blight or fruit rot. Surface moisture and moderately warm temperatures encourage its development.
- Fruit damaged by wind, hail, insects, or mechanical means is more susceptible to this organism. Infected blossoms are brown and water-soaked.
- The fungus grows down the pedicel into the stem which may cause twig dieback.
- Diseased blossoms and fruit generally become covered with “tufts” of brown fungal material. Fruit infection usually occurs near maturity.
- The fungal organism overwinters in mummies, stem cankers and old fruit peduncles.
- Control is by repeated fungicide applications and sanitation.
3.Bacterial Spot of Plum: Xanthomonas campestris pv. Pruni
- Symptoms are observed first as small, irregularly shaped lesions. The spots are pale green in contrast to the dark green surrounding tissue.
- In advanced stages, angular lesions are formed, surrounded by a halo of lighter coloured tissue. The inner portion of the lesion turns black and drops out.
- This gives the leaf a “ragged” or “shot hole” appearance. Leaves heavily infected with bacterial spot turn yellow and fall.
- Leaf spots are concentrated toward the distal end of the leaf. Fruit infection is not as common as foliage infection.
- When it occurs, small spots develop and gum may flow from these spots.
- Highly susceptible varieties like Methley and Santa Rosa are more likely to have fruit infections than Morris, Bruce or Ozark Premier.
- The bacterium overwinters on infected twigs.
- Chemical control has not been highly effective. Early and late dormant copper sprays will aid in control. Optimum nutrition is also important.
- TamilNadu Agritech Portal