Angular Leaf Spot

Pseudomonas lachrymans

Another bacterial leaf disease that infects members of the Cucurbit family (cucumber, squash, melons and watermelons). Like most bacterial diseases it is most prevalent in warm (75-85˚ F) and wet or humid weather.

This infection is characterized by water-soaked, gray angular spots (angular because they occur between the veins) in the leaves. These eventually dry up, turn brown and tear, leaving small angular holes. Lower leaves may eventually turn completely brown and die. The immature fruits develop small water soaked spots (these eventually turn white) and may drop off. These may also be lesions on the stem, oozing bacterial slime.

Infection usually comes from bacteria on crop debris (it can live 2 years in crop debris) and is spread by water in the form of rain or overhead sprinklers. Prevent problems by cleaning up in fall, rotating crops annually, removing infected plants, using drip irrigation and not touching wet plants. Some varieties have resistance to angular leaf spot.

Angular Leaf Spot can also be seed borne. If you suspect seeds are infected, soak them in hot water (127 degrees F for 25 minutes) or a solution of 1 part bleach to 10 parts water (for 30 minutes).

Image: Howard F. Schwartz, Colorado State University, Bugwood.org