Question
I have a white fungus infection on my holly tree leaves. The fungus is rectangular in shape on the back of the leaves only, and the leaves are turning brown and falling off when infected.
I have severely clipped the tree and presently have no leaves left on it. I have also disposed of all the clippings into a refuse bin. Will constant watering, or soapy water cure it?

Answer
Sounds like a disease called 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.

the best method to control this disease is to use fungicides.  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).
Check with your local nursery/garden type store for a fungicide for powdery mildew.



Non-Chemical Control
昉rune diseased areas of your plant and discard. The effectiveness of ammonium, potassium and sodium bicarbonates, the ingredient in baking soda, has been found successful against powdery mildew. This treatment will not harm the environment and is safe for consumers. Although experts are still arguing whether this treatment is best to prevent powdery mildew rather than treat it, it is an alternative worth keeping in mind. Four tsp. of baking soda to one gallon of water sprayed on your plant once every two weeks is recommended. Do not over spray as the bicarbonate can build up in your soil and create another problem for your bush or tree.


I would water it with 1 inch of water per week-place a pan under the tree and trun the sprinkler on and when the pan has 1 inch of water in it stop. This will give it a deep watering and should encourage it to leaf out again.