Identification

• Powdery mildew is a disease caused by fungi, which affect a wide variety of ornamental grasses, trees, flowers, vegetable plants and shrubs. Powdery mildew fungi causes similar symptoms on all host plants. Sycamore trees with powdery mildew may exhibit severe symptoms in warm, dry weather. Powdery mildew fungi do not need moisture to germinate and prolonged periods of rain actually slow disease development. According to Colorado State University, the severity of powdery mildew depends on the host plant, age of the plant, overall health of the host and weather conditions.
  
  

Effects

• Sycamores with powdery mildew develop a white, fuzzy fungal coating on leaves and stems. Leaves infected with this fungus, often become distorted and turn yellow. Infected flower buds typically do not open and sycamore leaves may drop to the ground prematurely. Eventually, white fungus covers the majority of the tree. The fungus does not attack leaf tissues, but remains on leaf surfaces. Fungal spores are spread through splashing water or carried on the wind to infect other plants and trees in close proximity.
  
  

Cultural Control

• If powdery mildew is a problem on your sycamores, sanitation is important to prevent spread of the disease. Avoid using overhead watering systems to water your plants and trees. Do not apply nitrogen rich fertilizers to your sycamore tree, as this promotes new growth -- a favored host of powdery mildew fungi. Remove all infected plant debris and destroy it. Do not use infected plant debris for compost.
  
  

Chemical Control

• Severe powdery mildew infections may require chemical control methods in conjunction with cultural controls. Applying a fungicide with the active ingredients sulfur, neem oil or potassium bicarbonate may help prevent powdery mildew. During the growing season, apply these products every 7 to 14 days for best results.