Angular Leaf Spot
(Pseudomonas syringae pv. lachrymans)
This is a bacterial disease causing dark, angular spots between leaf veins; tear shaped droplets ooze from infected tissue. As the leaf dries and turns grey, leaf tissue tears and shrinks. Fruit may exhibit circular spots or rotted areas.
Hosts
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Cucurbits (cucumber, squash), a similar strain infects beans.
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Squash
Lifecycle
The bacteria over winters in plant debris and can persist for more than two years on dry leaves. It enters the plant through wounds or natural openings under wet conditions, then can be spread mechanically. Angular leaf spot is also seed borne (treat seed for 20 minutes with 120°F. water).
Controls
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Cultural
Use 2 year rotations between cucurbit crops. Avoid wetting foliage with irrigation water. Use resistant cultivars when possible. Plant on raised beds. Excessive nitrogen fertilizer increases disease severity.
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Chemical
Copper can be sprayed to protect leaves when weather is wet and warm.
