Species

Angular leaf spot (Pseudomonas syringae pv. Lachrymans).

Host/site

Angular leaf spot affects members of the cucurbit family such as cucumbers and melons. The disease most commonly occurs in cucumbers. The disease is especially widespread after frequent summer rains.

Identification

Appearance and Indicators

• Lesions appear on plant foliage as water soaked spots that later turn light gray or tan.
• Spots may initially have a yellow halo and the affected tissue may fall out as it dries.
• Veins outline the lesions, giving the spots an angular appearance.
• Sometimes lesions also appear on the fruit itself, also with a yellow halo around them.
• Squash lesions are smaller than those on the foliage and the center of these lesions may be white.

  Life cycle

• The pathogen overwinters in dead plant material.
• It will not survive for long in water or soil.
• When the seed germinates, it becomes infected and the bacterium multiplies.
• Water from rain or sprinklers spreads h3. the bacteria from plant to plant. Bacteria can also be carried on insects or on garden tools.

Natural Enemies

Not applicable

Monitoring

If lesions are spotted on plants in the garden, check surrounding plants for any sign of the disease. Once the disease is positively identified, action should be taken to avoid further spread.

Action Thresholds

Since the disease can be spread by water, it is best to employ the cultural controls mentioned below if you have positively identified angular leaf spot on plants in the garden.

Cultural and Physical Controls

• Limit the use of overhead sprinklers.
• Pick fruit when the vines are dry to prevent spread in the garden.
• At the end of the season, debris from the garden should be destroyed to decrease overwintering and disease spread next year.
• Resistant cucumber varieties are available. Consult your local nursery for current information on resistant varieties.
• Remove infected leaves and plants

Biological Controls

N/A

Chemical Controls

The suggested organic chemical treatment is a bactericide (fixed copper). Copper can be harsh on the environment, especially wetlands and riparian areas, even though it is approved for organic agriculture.

References

Davis, R.M. "UC IPM: UC Management Guidelines for Angular Leaf Spot on Cucurbits." University of California IPM. June 2008.
<http://www.ipm.ucdavis.edu/PMG/r116101511.html>
"RPD No. 919 - Angular Lead Spot on Cucurbits." University of Illinois IPM. November 1999. http://ipm.illinois.edu/diseases/series900/rpd919/
Venette, J.R. "Angular Leadspot of Cucumber." North Dakota State University Extension. July 1996. <http://www.ag.ndsu.edu/pubs/plantsci/hortcrop/pp738w.htm>