Disease in the Garden

Prevention is essential to reduce powdery mildew.

Powdery Mildew on Turtlehead - Blog Photo

This has been a banner season for powdery mildew. High humidity and warm daytime temperatures combined with cool temperatures at night are just the environmental conditions the fungus needs to run rampant across the flora in our landscapes.

Powdery Mildew Close Up - Blog Photo

Powdery mildew is easy to identify. It looks like its name implies – white powdery blotches on leaves, stems, flowers or fruits of plants. In severe instances, leaves may look like they’ve been sprinkled with a powdery dust.

This fungus overwinters in plant debris and starts producing spores in the spring. These spores are carried by splashing water or the wind to healthy plants. Spores can also travel by way of insects.

Powdery Mildew on Rose - Blog Photo

Although powdery mildew is unsightly, it rarely kills plants. In serious infestations, it may weaken the plant, leaves might yellow and drop, and buds may fail to open. The fungus for powdery mildew can only infect its specific host plant. The powdery mildew on your cucumber plant cannot infect your roses.

Powdery Mildew on Bee Balm - Blog Photo

Some plants are more susceptible than others to powdery mildew. Lilacs, honeysuckle, roses, ninebarks, phlox, bee balm, sweet peas, dahlias, grapes, squash and cucumbers are some of its favorite targets.

It is easier to prevent powdery mildew than to cure it.

Good sanitation is vital to prevention. If you’ve had a problem with powdery mildew in the past, be sure to remove and destroy all parts of annuals, perennials and vegetable plants that may have hosted the disease in the fall so it can’t overwinter in your garden.

Provide good air circulation between plants to reduce humidity. Space plants properly resisting the temptation to pack them close together. Prune excess stems from established plants to increase air circulation.

Grow cucumbers on a trellis to reduce powdery mildew.
Grow cucumbers on a trellis to reduce powdery mildew.

To further reduce humidity, avoid overhead watering, especially late in the day. Support mildew-prone vining plants on trellises instead of letting them sprawl on the ground.

Always purchase healthy plants and provide their recommended cultural needs. Plant them in the conditions they prefer and then water, fertilize and prune them properly.

Jacob Kline bee balm has superior mildew resistance.
Jacob Kline bee balm has superior mildew resistance.

When you purchase plants, choose mildew-resistant varieties. Many newer cultivars have been bred for mildew resistance. If you already have some plants frequently affected, consider replacing them with their new and improved versions. One caution: mildew resistant means the plant can resist mildew spores but are not completely immune to them. To ensure the best health, continue to follow the previous methods of prevention.

If all else fails, there are fungicides available to treat powdery mildew. Choose one labeled for use on the plant you intend to treat, and always follow the directions on the label and apply carefully.

Reduce the risk of powdery mildew in your landscape by practicing prevention strategies, inspecting your garden regularly, and acting quickly when see the first signs of the fungus. Garden with me!

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