Powdery mildew is a fungal disease that infects a variety of plants. Plants
affected with the disease appear to have been sprinkled with flour or talcum
powder. Leaves, flowers and stems may distort, turn yellow or drop. Buds may
fail to open. Tender, succulent tissues are the most susceptible to infection.
Powdery mildew damages plants by reducing photosynthesis and diverting
nutrients in the plant for their own growth and development. Repeated infections
stress plants as a result. Powdery mildew is host specific. The mildew that
appears on roses, for example, will not infect lilacs or vice-versa.
Good cultural practices are the key to disease management.
- Clean up plant debris in the fall. Powdery mildew over-winters on the
debris. In the following growing season, under correct temperature and
humidity conditions for the species, the fungus germinates and infects plant
tissue. Removing the debris reduces the amount of inoculum present the
following year.
- Improve air circulation in and around susceptible plants. Dense plantings
create ideal conditions for mildew development. Humidity is higher in such
plants and air doesn’t circulate well. Judicial pruning increases air
circulation, reducing humidity and decreasing the likelihood of mildew
development. Spacing and siting plants correctly at planting time has the
same effect.
- Avoid or minimize overhead irrigation, particularly late in the day, to
keep humidity low in and around the plant.
Other treatments include;
- Hosing off the plant with water early in the day. Free water is
detrimental to powdery mildew.
- Apply recommended fungicides.
- Apply neem-based products labeled for powdery mildew.
- Apply sulfur according to label directions. Avoid hot weather.
