Question
QUESTION: We have a Bradford pear tree in our backyard that is about 4-5 years old. It has been growing great. This year I noticed the bottom half of the tree has a white substance on the leaves,and they also have brown spots on them. The tips of the leafs are curling up. The rest of the tree fine. Is this a type of fungus? I cannot see any bugs,worms or other insects on the tree. They bark is intact and looks healthy. What should I do to prevent this? Can I treat the tree with something? What would you recommend.   Thank you

ANSWER: Sounds like powdery mildew.

Powdery mildews, as the name implies, often appear as a superficial white or gray powdery growth of fungus over the surface of leaves, stems, flowers, or fruit of affected plants. These patches may enlarge until they cover the entire leaf on one or both sides. Young foliage and shoots may be particularly susceptible. Leaf curling and twisting may be noted before the fungus is noticed. Severe powdery mildew infection will result in yellowed leaves, dried and brown leaves, and disfigured shoots and flowers. Although it usually is not a fatal disease, powdery mildew may hasten plant defoliation and fall dormancy, and the infected plant may become extremely unsightly.

In many cases, powdery mildew diseases do little damage to overall plant health, and yearly infections can be ignored if unsightliness is not a major concern. For example, lilacs can have powdery mildew each year, with little or no apparent effect on plant health. On some plants, powdery mildews can result in significant damage. Thus, fungicides must be used to achieve acceptable control. For best results with fungicides, spray programs must begin as soon as mildews are detected. Spray on a regular schedule, more often during cool, damp weather. Use a good spreader-sticker with the fungicides. Be sure and cover both surfaces of all leaves with the spray. Fungicides generally recommended for powdery mildew control include: Triadimefon (Bayleton, Strike); Triforine (Funginex), Thiophanate-methyl (Cleary's 3336, Domain# and Propiconazole #Banner).


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QUESTION: Thank you Jim...the above answer seems exactly what is going on with our tree. I wanted your opinion on the application of the above mentioned fungicides. Should the entire tree be sprayed or only the effected areas? Should I treat the tree as a preventive.... even if no signs of infection are present? Does the fungicide have to be applied for a certain number of applications or is it until the tree looks normal again?  Thank you

Answer
I would spray the areas that have the mildew and adjacent areas. IF you can it would not hurt to spray the whole tree. These are effective only on contact, so applications must thoroughly cover all susceptible plant parts. As plants grow and produce new tissue, additional applications may be necessary at 7- to 10-day intervals as long as conditions favor disease growth.  Environmental conditions that favor the growth of downy mildew are different from those that favor powdery mildew and include low temperatures of 50?to 70癋, a relative humidity of 90% or higher, and free moisture.  Although relative humidity requirements for germination vary, all powdery mildew species can germinate and infect in the absence of free water. In fact, water on plant surfaces for extended periods inhibits germination and kills the spores of most powdery mildew fungi. Moderate temperatures of 60?to 80癋 and shady conditions generally are the most favorable for powdery mildew development. Powdery mildew spores and mycelium are sensitive to extreme heat and sunlight, and leaf temperatures above 95癋 may kill the fungus.