Plant Protection Knowledge
Angular leaf spot is commonly found on cucumber during rainy season, and can cause serious yield and quality loss to cucumbers.
The bacterium, Pseudomonas syringae pv. lachrymans (Pseudomonas lachrymans), also infects other cucurbits including zucchini, squash, honeydew melon, muskmelon, and watermelon.
Heavy infections of cucumber can occur during the rainy season when plant tissues become filled with water.
Symptoms
Leaves
© A. A. Seif@ infonet-biovision
Small angular water-soaked spots may develop on the leaves. The spots are confined by leaf veins and appear tan on the upper surface and gummy or shiny below. As the lesions age, their colour changes from gray to white, dead tissue falls away, leaving small angular (square) holes in the leaf
Fruits
Infections on fruits are first small, circular, water-soaked and soft but older lesions are chalky and cracked. Fruit spots usually occur when fruits are about half grown. Below the lesions, flesh may be brown down to the seed layer. If attacked when very young, the fruit may fall off the plant. Lesions on stems may be covered with abundant bacterial slime
Cultural control
- Grow cucumbers from clean seed in an area isolated from other cucurbit fields and on land that has been free of cucurbits for one or two years.
- Avoid excessive overhead irrigation or excessive amounts of nitrogen fertilizer.
- Do not work the cucumber field when plants are wet since water helps spread the disease.
- Debris from the crop should be destroyed to decrease the spread of the disease to other fields.
Chemical Control
-
Copper containing fungicidal sprays can help control the disease. A weekly copper spray schedule is advisable when weather is favourable for disease spread (above 75°F and wet).
-
Copper sprays should not be continued in dry weather, especially hot, dry weather, because the sprays may cause plant injury.