Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Angular leaf spot (ALS) is a common disease of cucumber in warm, humid conditions. However, it does infect other cucurbits such as squash. Symptoms on cucumber and other cucurbits appear first as small water soaked spots that eventually expand to the veins. Because they are delimited by the vein, they appear angular. Infected tissue may dry and crack, giving a tan, tattered look. Fruit can also be infected. The pathogen is the bacterium Pseudomonas syringae p.v. lachrymans, which can be seed borne. The pathogen spreads from plant to plant in splashing rain, irrigation, or mechanically (such as on hands, windblown sand, or equipment).
Management begins with the use of clean seed and host resistance where possible. A two year rotation will reduce initial pathogen inoculum in soil. In season copper sprays can reduce spread of the disease.
Angular leaf spot of cucumber (Pseudomonas syringae pv. lachrymans) on cucumber.
Charles Averre, North Carolina State University, Bugwood.org