Mildews that produce diseases in plants are of two diverse types, powdery mildew, and downy mildew. Although they have alike names, they are different, having dissimilar control measures and symptoms.
Powdery mildew is the most familiar type of mildew. It can be seen on most ornamental plants like privet, crab apple, turfgrass, phlox, monarda, azaleas, roses, lilac, dogwood, grape, and squash. There are several kinds of powdery mildew. It’s host-specific so that the organism that produces mold on grapes, for instance, can’t create mildew on lilacs.
Powdery mildew is typically known by the white cobweb-like growth of the mycelium on the upper exterior of the leaf that sometimes occurs on the underside of leaves as well as on stems, buds, flowers, and young fruit.
Leaves that are infected usually curl, get brown and distorted, and fall off prematurely. Infected buds don’t open. Though the effects of powdery are ugly and deteriorate the plant, mildew hardly ever kills it. The fungus gets its nourishment from the top part of cells and doesn’t invade the tissues under them.
Downy mildew is less common. However, it can be very detrimental to plants. It affects a wide variety of plants including butterfly bush, pansy, cucumbers, mint, roses, coreopsis, snapdragon, and viburnum. The symptoms differ based on the host plant but typically can be seen as dark yellow, or light green spots on the upper exteriors of leaves.
As the disease advances, the leaves turn brown and fall from the plant. Also, brown to fluffy gray masses might appear beneath the leaf as discoloration. Downy mildews infiltrate the leaf tissue for nourishment, creating more serious damage.
Powdery mildew and downy mildew thrive in high humidity and damp conditions, particularly when crowded, and air circulation is bad. Powdery mildews prefer temps around 60-80. Downy mildews like temps somewhere between 50-75F. Both might subside when summer temperatures rise into the 90s.
Control of both mildew types can be somewhat supported by proper growing techniques like:
- An assortment of resistant varieties
- Enhancement of air circulation by the accurate spacing of plants
- Demolition and elimination of infested plant parts
- Using drip irrigation rather than overhead watering
- Cleaning of tools that are used on infected plant
- Removal of plant debris that may harbor pathogenic spores
When infestations get serious, more drastic measures might be needed like chemical controls. This job should be done by a Tampa tree service professional.