Plum leaf blotch (Polystigma rubrum) – identify and control
Plum leaf blotch, Polystigma rubrum, frequently occurs in years with rainy springs, particularly in neglected orchards or on old plum trees. The disease causes defoliation, and the fruit remains small and low in sugar.
Symptoms – Plum leaf blotch
The disease manifests itself towards the end of May and the beginning of June when roughly circular spots appear on the affected leaves At first they turn yellow-cream, then they turn orange, and finally red-brick. The tissues near the spots thicken, become crusty, waxy in appearance, and bulge slightly toward the underside of the leaves.
In wet weather, the pycnospores are removed from the pycnidia and appear on the underside of the leaves next to the spots as a white jelly layer. In favorable years of the disease, as a result of intense attacks, the leaves dry out and fall early. This causes a weakening of the trees’ resistance to winter frosts.
The pathogen is Polystigma rubrum. It is transmitted from one year to another by plant debris left on the soil. During vegetation, the pathogen produces numerous generations of pycnidia with pycnospores that produce secondary infections.
Prevention and control. Disease prevention can be achieved by growing resistant plum tree varieties and by deep plowing to bury attacked leaves. When the disease is observed, it is recommended to apply treatments with specific fungicides.
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