I have two words for you: powdery mildew. This is shaping up to be the wettest June on record. Not just wet, but the wettest. Fungus loves heat and wet weather and that is just what we have right now.
By Chris Cohan
I have two words for you: powdery mildew. This is shaping up to be the wettest June on record. Not just wet, but the wettest. Fungus loves heat and wet weather and that is just what we have right now.
Powdery mildew is a well-known nuisance for phlox, lilac, bee balm, peonies, and roses. As the name implies, this fungus looks like powdery splotches of white or gray, on the leaves and stems of plants. The disease tends to start on the lower leaves and work upward. By the end of the summer, lower leaves are usually wilted and dead while upper leaves are coated with the fungus.
In addition to detracting from the beauty of these flowering plants, powdery mildew weakens perennials especially phlox and bee balm. The fungus has specialized structures that penetrate leaf tissue and absorb nutrients.
Management of powdery mildew is aimed at preventing the conditions that favor the fungus.
Space plants adequately to allow good air movement throughout the foliage.
Water plants early in the day, so leaves dry quickly.
Do not over-fertilize (especially with nitrogen).
Remove diseased plant debris at the end of the season to minimize survival of the fungus over the winter.
In addition to following these good cultivating practices, regular fungicide sprays (we recommend Safer’s natural variety) can be used to protect the leaves of the plants. Spraying will not cure the leaves of the disease, so the fungicide must be applied early and repeatedly, and according to the product label directions.
Some phlox cultivars — David (white), Orange Perfection (dark salmon), Prime Minister (white, red eye), and Starfire (red) — show tolerance to the powdery fungus.
Baking soda is an inexpensive way to control powdery mildew. It’s most effect as a preventative measure, offering only minimal benefits once your plants have become infected. Weekly spraying of susceptible plants during humid or damp weather can greatly reduce the incidence of powdery mildew in your garden.
Mix together:
1 tablespoon of baking soda
½ teaspoon of liquid soap (helps mix to cling and spread over leaves)
1 gallon of water
1 tablespoon of horticultural oil (smothers fungi)
Water your infected plants well a few days before applying this mixture, and don’t apply it in full sun. This brew may help in combating black spot, rust, and anthracnose, too. It can, however, burn the leaves of some plants. Do not store unused mixture.
In addition to spraying, you must remove all heavily infected leaves. Fortunately, the infection starts at the bottom and works its way up. If you get cracking, your plants will still have a fighting chance.
Peonies now past bloom should be mercilessly pruned way down. This provides improved air circulation and more light to perennial beds. Follow by cleaning all planter beds of fallen leaves.
If you have a sprinkler system, back it way off until this reign of rain stabilizes.
Since you are going to spray your lilacs, bring your clippers to remove all dead flowers now. Allow me to repeat, NOW. The classic lilac pruning mistake is to wait too long to prune, and then lose next season’s blooms. Follow by cutting back new tender leaf growth by half to promote more fragrant blooms on your Syringa vulgaris. Who could have named this garden treasure, vulgaris? It is anything but.
