How to Manage Pests
UC Pest Management Guidelines
Angular Leaf Spot
Pathogen: Pseudomonas syringae pv. lachrymans
(Reviewed 11/05, updated 6/08, pesticides updated 5/16)
In this Guideline:
Symptoms and Signs
Angular leaf spot occurs most commonly on cucumber, but is also found on melons in California. Lesions on the foliage begin as water-soaked spots that later turn gray or tan. Spots may initially develop a yellow halo. As the affected tissue dries, the internal tissue may fall out, giving the leaf a tattered appearance. The lesions are delimited by veins, giving them an angular shape. Fruit lesions are usually superficial.
Comments on the Disease
The bacterium survives on infected plant debris in the soil or on seed. Humid conditions favor development of the disease. Rain or overhead irrigation leads to rapid spread. The disease is also spread by workers picking fruit or machinery passing through the field.
Resistant cucumber varieties are available. Limit the use of overhead irrigation. Pick fruit when the vines are dry to prevent spread in the field. Use pathogen-free seed and rotate out of cucurbits. Treat when symptoms first appear if the weather is predicted to be cool and rainy.
UC IPM Pest Management Guidelines: Cucurbits
R. M. Davis, Plant Pathology, UC Davis
Acknowledgment for contributions to Diseases:W. D. Gubler, Plant Pathology, UC Davis