VEIN SPOT
Vein spot disease is caused by the fungus Gnomonia nerviseda. The symptoms of the disease are similar to the leaf lesion symptoms of scab disease, but vein spot disease, unlike scab disease, affects only the leaves. Lesions of vein spot disease develop on the veins or stems of leaflets and leaves, are usually less than one-fourth inch in diameter and are characteristically dark brown to black. Leaflets and leaf stems which are severely affected drop, resulting in premature defoliation.
The fungus lives in fallen leaves over the winter. The following spring when temperature and moisture conditions are favorable, spores formed in special structures called perithecia are forcibly discharged into the air and carried by wind currents to the newly formed spring foliage, initiating primary infections.
Control.—See spray schedule, [page 4].