Midsummer humidity can bring on the ugly gray fuzz of powdery mildew on your roses and perennials. While perennials that are watered well are somewhat more resistant, eventually even the healthiest plants can succumb during hot, humid weather. Many fungicides can be found in the garden center, but some bear warning labels that make gardeners think twice. Fungicides can also damage the soil food web that keeps our plants healthy. Instead, tackle powdery mildew with gentler natural controls first.

PREVENTION
Try to water your perennials in the morning so that the leaves can dry out during the day. While moisture is necessary for this fungus to grow, don't be afraid of dousing the leaves of smooth-leaved plants. In fact, washing the leaves down while watering can wash off fungal spores. Fuzzy-leaved plants are more often adapted to desert environments and do better if the are watered with a soaker hose or drip system so that their leaves stay dry.

If certain plants are mildew-prone, keep the ground around them raked clean of dead leaves. Mulch the ground to keep soil off of the leaves. Or consider removing the plant entirely and replacing it with something that is more resistant to the fungus.

BAKING SODA SPRAY
Another preventative is a spray made from baking soda, which creates a hostile environment for the fungal spores. Dissolve one tablespoon of baking soda in a gallon of water. Add 1/2 teaspoon of liquid soap (not detergent) and 1 tablespoon of horticultural oil. Shake well and pour into a sprayer. Spray plants once every two or three weeks after they have been watered well. Re-apply after a rainfall. This mixture is known as the Cornell formula, and has been shown by Cornell University to be nearly as effective against powdery mildew and black spot on roses as most commercial fungicides.

IF MILDEW STRIKES
As the old saying goes, an ounce of prevention is worth a pound of cure. Plain water and the baking soda spray are excellent preventatives, but once mildew invades your garden, even strong fungicides from the garden center won't cure it. The best treatment is a severe pruning. Cut away all affected parts of the plant, even if it means pruning a perennial down to the ground. Wash the remaining plant parts with plain water, water the plant well, and after it dries, spray with the Cornell baking soda mixture. When new growth emerges, continue treatment until you're sure the new growth is healthy.

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