Why you should take steps if you see a grayish powder on your plants. It’s powdery mildew
PHOTO: Yueke
As the growing season advances, be on the lookout for a white or grayish-white powder on your plants. This is powdery mildew, a fungus that can affect a broad spectrum of fruits, vegetables, and flowers, covering their leaves, stems, blossoms, and, in severe cases, entire plants. It's not a sight for sore eyes.
Certain plants are more prone to infection, with hydrangeas, lilacs, phlox, and peonies being the most susceptible. Other vulnerable species include azaleas, blueberries, dahlias, delphinium, cucumbers, euonymus, lilacs, rhododendrons, roses, snapdragon, spirea, squash, wisteria, and zinnias. If you grow any of these, keep a close watch for symptoms.
The silver lining is that powdery mildew typically won't kill your plants unless the infection is incredibly severe.
However, if left unattended, leaves may curl and turn yellow or brown, flowers may drop, and bloom periods may be abbreviated. The fungus can also weaken plants and stunt their growth, hindering photosynthesis and reducing their nutrient absorption capabilities.
WHAT SHOULD YOU DO?
As soon as you detect the powdery coating that characterizes the disease, remove the affected leaves and discard them in the trash. Don't leave them lying around because their spores can continue to infect neighboring plants.
If the disease has spread beyond a few leaves or you're witnessing a worsening of symptoms, apply horticultural or Neem oil as directed on the package.
Alternatively, combine 1 tablespoon of baking soda with 1/2 teaspoon of horticultural oil or liquid dish soap (not dishwasher detergent) in a gallon of water, and spray the entire plant, including the undersides of the leaves, with the solution.
While baking soda isn't a fungicide, its alkalinity hinders the germination of spores, which prefer acidic environments. As the pH balance is restored, the fungus will start to grow again, so repeated applications may be necessary. Nonetheless, be cautious not to overapply, as baking soda contains salt, and excessive salt can harm plants.
Dealing with severe infections necessitates the use of synthetic, sulfur-based, or biological fungicides.
If your plants have been affected before, proactively treating them with your chosen fungicide can help prevent another outbreak.
GENERAL PRECAUTIONS
Powdery mildew typically emerges in spring or early summer. Although it flourishes in warm, humid conditions, it can also be found in cooler climates. Simple, non-chemical strategies can significantly reduce the risk of infection wherever you garden.
• Plant resistant varieties of plants, if available.
• Ensure that plants that thrive in sunlight receive at least 6 hours of direct sunlight daily.
• Plant young plants with proper spacing in mind, considering their mature sizes, and divide overgrown plants. Overcrowding retains moisture, which promotes mold, mildew, and fungal diseases.
• Avoid overhead irrigation. Instead, direct water to the soil above the root zone.
• Prune branches and stems regularly to improve airflow and expose more plant parts to sunlight.
• Remove fallen leaves and plant debris from the garden beds when your plants become infected to prevent further spread and recurrence.