Back to Diseases of cucurbits
Angular leaf spot
Clemson University, Bugwood.org
Angular leaf spot is a bacterial disease caused by Pseudomonas syringae pv. lachrymans. Although angular leaf spot can occur on any of the cucurbit crops, cucumber is less commonly affected due to the availability of resistant varieties.
- Leaves develop small, angular, brown or straw-colored spots with a yellow halo.
- Leaf spots dry and drop out, leaving irregularly shaped holes in the leaves.
- Water soaked to tan small circular spots on fruit.
- Bacterial soft rot often develops after fruit spots and rot the entire fruit.
- Sticky drops of whitish liquid form on the underside of the leaf when wet, dry to a crust when dry.
C. Averre, NCSU Bugwood.org
Angular leaf spot thrives in warm humid conditions. The bacteria can infect all cucurbit crops and will infect all above ground parts of the plant including leaves, fruit and vines. When fruit are infected, the bacteria moves deep into the fruit and infects the seed.
The disease can be introduced into a field through contaminated seed. When humidity is high, a drop of clear to white sticky bacterial ooze forms on infections. These bacteria are moved from plant to plant on the hands and tools of workers, by insects, or by splashing water. The pathogen can survive in plant debris for over 2 years.
- Many resistant varieties are available for cucumbers and are the best form of control for this crop.
- Buy clean seed from a reputable source. If saving seed, do not collect seed from infected plants.
- Rotate vegetables so 2 or more years go by before planting any member of the squash family in the same location.
- Use drip irrigation instead of overhead sprinklers if possible.
- Do not work in plants when leaves are wet.
- Remove and destroy infected fruit and vines at the end of the season in small gardens.
- In large fields, till in infected plant debris at the end of the season to speed up decomposition.
- Copper can slow the spread of disease if the infection is caught early. Sprays are not effective once disease is severe. Sprays do not need to be continued if dry weather persists beyond 2 weeks.