Black Knot Spot symptoms on Plum
Black Knot (fungus -
Apiosporina morbosum): Affected limbs and twigs are malformed as a result
of black woody growths (galls). The galls are similar to those caused by crown
gall on the root system. The disease is more prevalent on the small twigs, but
under severe disease conditions it may be found on large limbs. Infection of new
shoots occurs from bloom until shuck split stage. Primary inoculum comes from
one to two year old galls. Control of black knot is by sanitation, chemicals and
resistant varieties. Prune and destroy the galled tissue. Make cuts two or three
inches below the gall to insure complete removal of the fungus. Fungicides
applied for other diseases in the early bloom periods will help reduce the
occurrence of this disease.
January, 1995
