Disease 2 - Powdery Mildew on Cucurbits and Rose

Above are two photos of powdery mildew on pumpkin.

Below are photos of infection of a climbing rose : 






Powdery Mildew applies to a group of related fungi. 

Host Range : 

Generally a particular species of powdery mildew is restricted to one host, or a group of related hosts. Ornamentals, fruit, field crops and weeds are affected. Roses, apple, cucurbits, grape, strawberry, peas and beans are commonly affected. 

Symptoms : 

Almost all begin as faint white spots on leaves. The spots gradually increase in size until the whole leaf is covered in white powder. Buds, stems and fruit are also affected. 

Leaves that are fully formed are not changed, but young leaves can curl up or pucker. 

Disease Cycle :

Powdery mildew spores generally require high humidity for germination. Some flourish under dry hot conditions, but germinate when there is night dew. They do not germinate in rainy weather. Once it gets going, can continue to grow even in dry conditions. Optimal temp range for infection is 11-28 degrees celsius. 

Control : 

cultural - providing good ventilation through adequate spacing, choose the least susceptible varieties, avoid overhead watering, don't water in evening in favourable conditions. Prune off all infected shoots and burn them. 

chemical  -  in commercial crops, spray as soon as disease is noticed with wettable sulphur (2-4g per litre of water). Do not use in hot weather (scorch) or in dehydrated plants. Also systemic fungicides.