Causal Agent: 

Fungi (Oidium sp.; Oidiopsis sp.)

Characteristic Symptoms:
Affected leaf consists of white powdery mold/pustules on the upper leaf surface (caused by Oidium sp.).
Yellowing of the leaf is observed in tomato leaves infected by Oidiopsis sp. White powdery mold is observed on the lower side of the leaf.
Conditions for Disease Development:
The disease is common in greenhouse-grown tomatoes and in damp, shaded areas.
Spores can germinate at any relative humidity when  temperature is cool (15-25°C).
Once infection has occurred, warm days (above 30°C) with cool (below 25°C) and humid nights favour rapid disease development. 
Spores are carried by wind to new hosts.
Disease incidence is greater using furrow or drip irrigation than using overhead irrigation. Spore germination is inhibited by water on plant surfaces for extended periods. 
Management and Control:
Avoid planting in low, shady areas or increase light intensity in the area.
Provide good air circulation to minimize disease incidence and severity.
Avoid excessive use of N fertilizer or use a slow-release fertilizer.
Remove weeds that may serve as alternate hosts of the fungus.
Avoid furrow irrigation when infection is high.
Apply sulfur-based fungicide  (e.g. Kumulus®) or thiophanate-methyl (e.g. Tango, Topsin®) at the early sign of the disease. 
When plants are susceptible, apply protectant and curative fungicides such as azoxystrobin (Amistar®, MiradorⓇ, RobatoⓇ), difenoconazole (e.g. ScoreⓇ, MontanaⓇ, PursueⓇ, BashⓇ), tebuconazole (e.g. Folicur®).
Use resistant varieties, if available.
Compendium of Pepper Diseases-APS; Powdery Mildew on Vegetables (;; Tomato Powdery Mildew (

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