The region’s wetter-than-usual July is seeing an increase in powdery mildew while home gardeners and landscapers around the state are seeking a remedy to save plants.
The mildew, actually a group of fungi that attaches to the leaves and stems of plants, infect phlox, bee balm, and peonies. The surfaces of the plant appear to be dusted with baby powder-like specks.
According to Bonnie Kirn Donahue, a University of Vermont Extension master gardener and landscape designer, the spores are spread by wind. When the spores become attached to leaves and stems, the fungi gobble up nutrients from the plant to feed its growth and spread.
“While this sounds extreme and doesn’t look very nice if the affected plant is still growing and flowering as it should, you don’t need to do anything to treat the mildew,” she noted.
Kirn Donohue said the focus of concern by home gardeners is the fungus on phlox, Vermont’s most popular and highly versatile perennial. The garden plant blooms all summer even into the early autumn before frost.
“From spring-flowering, low-growing creeping phlox (Phlox subulata), to its taller, summer relative, garden phlox (Phlox paniculata), there are many cultivars with an endless variety of flower and leaf color, height, and bloom time,” she noted. “Unfortunately, phlox is susceptible to being eaten by animal visitors such as deer and being covered with an unattractive, white substance known as powdery mildew.
According to Kirn Donohue, if you notice that your phlox is suffering from stunted growth, dying foliage, or decreased flowering, or if you want to test out possible improvements, there are some non-chemical, pollinator-friendly methods you can use to manage fungi.
“When planting a new garden, try to select phlox varieties that are powdery-mildew resistant. This is a good step toward preventing future problems,” she said.
Here are fungus resistant types, the UVM master gardener recommends:
- Phlox paniculata ‘David’ is a 24-48-inch tall white-flowering garden phlox with resistance to powdery mildew.
- 26-30-inch Purple ‘Goliath’ phlox (Phlox paniculata ‘Goliath’),
- 36-inch salmon-toned ‘Orange Perfection’ (Phlox paniculata ‘Orange Perfection’)
- 12-20-inch light blue ‘Blue Flame’ phlox (Phlox paniculata ‘Blue Flame’) also are good choices for powdery mildew resistance
She also suggests gardeners try relocating phlox to a new place in their garden.
“Try an area that gets more sun and has more airflow to see if this makes a difference,” she advises. “Some varieties of powdery mildew prefer moist environments, while others are happy to live in dry conditions. If you have fungi and your environment is very shady, moist, and tightly spaced, relocating your phlox could make a difference.
The mildew explosion comes at the time of the 19th annual Phlox Fest at Summersweet Gardens at Perennial Pleasures Nursery and Tea Garden in East Hardwick, Vermont, which has guest speakers, garden tours, and an opportunity to view more than 160 phlox varieties in bloom.
Among the featured speakers is retired UVM Extension horticulturist, Dr. Leonard Perry.
The festival runs from July 31-Aug. 15. For details go to https://summersweetgardens. com/phlox-fest.