Causal Agent:
Fungi (Oidium sp.)
| Characteristic Symptoms: | |
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Affected leaf consists of white, talcum-like, powdery mold/pustules on the upper leaf surface. |
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Symptoms appear first on the older and shaded lower leaves. Infected leaves turn yellow, wither and die. |
| Conditions for Disease Development: | |
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The disease develops quickly under favorable conditions (dense plant growth and low light intensity). |
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High nitrogen fertilization, cool night temperatures, high relative humidity increase disease incidence and severity. Once the weather warms up, the plants tend to be able to outgrow the problem. |
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The optimum temperature for disease development is 20-27°C; Under field conditions, the disease stops at high temperatures (38°C and above). |
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The time between infection and symptom appearance is 3-7 days, in which large number of spores/conidia are produced. |
| Management and Control: | |
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Use resistant varieties, if available. |
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Avoid planting in low, shady areas or increase light intensity in the area. |
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Provide good air circulation to minimize disease incidence and severity. |
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Avoid excessive use of N fertilizer or use a slow-release fertilizer. |
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Remove volunteer crops and weed hosts that may serve as alternate hosts for the fungus. |
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Apply sulfur–based fungicides at the early sign of the disease. |
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When plants are susceptible, thorough application of protectant fungicides like azoxystrobin before the disease appears may be necessary. |
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