Causal Agent:
Fungus (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. |
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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 relative humidity is favourable for infection and conidia survival; however infection can occur at RH below 50%. |
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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.
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| 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 fungicide (e.g. Kumulus®) or thiophanate-methyl (e.g. Tango, Topsin®) at the early sign of the disease. |
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When plants are susceptible, thorough application of fungicides such as azoxystrobin (Amistar®, MiradorⓇ, RobatoⓇ), difenoconazole (e.g. ScoreⓇ, MontanaⓇ, PursueⓇ, BashⓇ), tebuconazole (e.g. Folicur®) is necessary to minimize infection. |
| References: | |
| Compendium of Cucurbit Diseases (1996) by the American Phytopathological Society | |
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