Angular Leaf Spots are very easy to distinguish since the plants suffering from this develop leaf spots that follow leaf veins. It is caused by bacteria such as Pseudomonas syringae (cucurbits) and Xanthomonas fragariae (strawberries) that survive in seeds and plant debris.
Symptoms
Once water soaked-spots appear on leaves, they spread rapidly when conditions get moist and ambient temperature is around 24-28 degree celcius. These spots expands upto a point they fill the area between leaf veins completely, but do not cross each other. Occasionally, older spots dry out and tear apart, leaving a hole at its place. On fruits, the spots appear as perfectly circular and water soaked and comparatively smaller than those on the leaves. The spots become powdery white and may crack the fruit open once the disease spreads. This contaminates fruits and causes fruit rot.
Biological Remedies
Use garlic solutions and hot water for around 30 minutes on infected seeding material. Use dehumidifiers in greenhouses to control night time humidity. It has also been found out that Pentaphage is lethal to Pseudomonas syringae, and organic copper fnngicides can slow the spread of the disease.
Chemical Control Measures
Pesticides containing copper hydroxide are most effective when the temperature is above 24 degree celcuis and the foliage is wet and are sprayed on a weekly basis. It is NOT recommended to spray the field on a hot day since it can seriously harm the plants.
Other Preventive Measures
Use furrow irrigation instead of sprinklers and avoid overwatering the field. Furthermore, do not sow crops in the field that have had cucurbits for at least 2 years.
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