Question
the leaves on my tulip tree are turning white, almost powdery looking.  do you know what this is

Answer
Sounds like powdery mildew. A powdery, fluffy white to light gray-colored fungus growth on succulent stems, leaves, buds and flowers is the characteristic symptom of powdery mildew. Young plants and actively growing shoots are more severely damaged than older plants, leaves or branches. Infected leaves may be dwarfed, curled or deformed. Powdery mildew can destroy the blossoms on crape myrtle. Small dead flecks in the leaves and defoliation may occur on some varieties of azalea and rhododendron that are infected with powdery mildew without the obvious development of white fungus growth.

The white mildew on the plant surface is actually composed of the threads (mycelium) and asexually produced spores (conidia) of the powdery mildew fungus. These spores are wind-blown to other parts of the same plant or other plants of the same species. Powdery mildew fungi are quite host-specific, so for example the mildew on zinnia will not spread to dogwood or sycamore, and vice-versa. Also, they are obligate parasites, meaning that they can only grow on living plant tissue.


Some powdery mildew fungi survive the winter as colonies of mycelium, but many switch over to sexual reproduction in the fall, producing minute brown to black specks amid the old mycelium on the dying leaf or other plant part. These survive the winter and in the spring release another type of spore to start the cycle over. Powdery mildew is a product of moist conditions and is usually seen in the wetter spring and fall seasons.

On many trees, the disease causes little or no damage, therefore, control is not necessary. There are fungicides that will control this disease but are not practical for use of large tree.

The following fungicides according to label instructions:

Propiconazole (Banner Maxx) is registered for control of powdery mildew and numerous other diseases on ornamentals.

Myclobutanil (Systhane, Eagle, and Immunox) is registered for control of powdery mildew and numerous other diseases on ornamentals.

Sulfur as a spray or dust as needed. Sulfur may cause some plant injury if applied when air temperature exceeds 90 F.

Triforine (Funginex) is labeled for use on roses and several other ornamentals. Follow manufacturer's instructions on the label. This product is only available in small packages.

Triadimefon (Bayleton and Strike) is now registered for use on a number of ornamentals.

Fenarimol (Rubigan) is a locally systemic fungicide for the prevention or therapeutic control of powdery mildew of field or landscape grown ornamentals.

In some situations copper fungicides will provide control of powdery mildew.

For large trees I would just rake the fallen leaves and move them off site to reduce the amount of spores for next year.