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.