Powdery Mildew

Severe powdery mildew conditions on leaves.

Powdery mildew is the dusty white coating that appears on the top of the leaves surfaces and are usually circular.  They appear in humid and warm conditions, such as densely growing plants.  They are able to withstand really cold days during winter and release their spores during spring.  They spread by wind or contact with infected plant materials.

The fungus can stunt the growth of plants, and usually kills the leaves - the leaves turn yellow and drop from the plant.  They suck up nutrients from the plant, so this causes a decline in growth in the production of the crops.

To control this fungus, we can remove the leaves if detected early.  Pruning overcrowded plants can help air circulation, which in turns reduces humidity.  Spraying of chemicals help as well, but it is more important to dispose of the infected leaves properly and not leave them on the floor.  Chemicals that can be used includes baking soda solution or lime-sulfur.

Source:
http://www.caes.uga.edu/extension/cobb/anr/Documents/Powdery.pdf