Powdery mildew is a fungal disease that affects a wide variety of plants. It is caused by various species of fungi in the order Erysiphales. Powdery mildew gets its name from the white or gray powdery spots that develop on the leaves, stems and fruits of infected plants. While not usually fatal, powdery mildew can seriously diminish the vigor and aesthetic appeal of plants. Fortunately, with prompt treatment and good cultural practices, powdery mildew can be controlled and its impacts minimized.

What Causes Powdery Mildew?

Powdery mildew fungi require living plant tissue to grow. Spores land on plant surfaces, germinate and send slender hyphae into the epidermal cells of the plant. The hyphae take nutrition from the plant cells. As the fungi grow, they send up erect conidiophores that produce large numbers of new spores on the surface growth. The spores easily dislodge and are spread by wind, water splash, and insects.

The fungi thrive in environments with high humidity and moderate temperatures. Powdery mildew often develops in late summer or fall when nights are cool and days are warm. Shady locations favor powdery mildew. Lush succulent growth resulting from heavy fertilization or excessive irrigation provides ideal conditions for powdery mildew infection. Stress weakens plants and makes them more susceptible.

Common Host Plants for Powdery Mildew

Many ornamental and edible plants can develop powdery mildew. Some of the most affected include:

• Roses
• Phlox
• Zinnias
• Bee balm
• Crepe myrtle
• Lilacs
• Dogwoods
• Squash family
• Cucumbers
• Melons
• Grape vines
• Apple trees

Powdery mildew fungi are very host specific. The powdery mildew on phlox will not spread to roses or vice versa. However, some plants like bee balm, monarda and oregano can be affected by more than one type of powdery mildew.

Signs of Powdery Mildew

The most diagnostic sign of powdery mildew is the superficial white to gray powdery growth that gives the disease its name. The powdery spots may appear on leaves, stems, buds, and fruits. These patches start off small but can enlarge and merge to cover entire plant surfaces.

On leaves, the discolored blotches may be limited by leaf veins. Infected leaves often curl upward, expose their undersides or drop prematurely. Flowers and fruits may be dwarfed, distorted or mottled by powdery mildew.

Checking leaf undersides with a hand lens will reveal a gray fuzzy growth made up of chains of spores and short hyphae. Severely infected leaves yellow and dry up. Dieback of twigs may occur in woody plants.

Preventing Powdery Mildew

Powdery mildew fungi mainly affect young succulent growth. Cultural practices that promote plant health and discourage lush growth are key to avoiding powdery mildew problems.

Choose resistant varieties – When buying plants prone to powdery mildew, look for cultivars labeled PM resistant. Resistant roses, phlox, bee balm, squash, grapes and cucumbers are available.

Provide good air circulation – Avoid overcrowding plants. Space them far enough apart and prune back encroaching branches to allow free air movement through foliage.

Water early in the day – Water at the base of plants. Wet foliage for prolonged periods promotes powdery mildew.

Apply mulch – A 2-4 inch layer of mulch conserves soil moisture and cools the soil. This discourages lush growth.

Scout regularly – Monitor susceptible plants frequently. Early detection and prompt removal of infected plant parts can prevent spread.

Apply fertilizer judiciously – Avoid excessive nitrogen. Promote plant health with moderate fertilization based on soil test results.

Prune selectively – Thinning cuts reduce density allowing air to circulate. Remove branches with powdery mildew.

Clean up debris – Rake up and dispose of fallen leaves and fruits which harbor spores.

Minimize stress – Choose plants suited to site conditions. Water, prune and fertilize appropriately to keep plants healthy.

Chemical Control Options for Powdery Mildew

If cultural methods fail to prevent powdery mildew, fungicide applications may be warranted. Treat early before mildew is widespread. Thorough coverage of all plant surfaces is essential. Repeat treatments every 7-14 days if needed. Rotate between fungicide classes to avoid resistance. Read and follow label directions carefully.

Some effective organic and synthetic fungicide options include:

Sulfur – Elemental sulfur and lime sulfur act as protectants against powdery mildew on roses, grapes, cucurbits and fruit trees. May burn plants if temperature is high.

Bicarbonates – Baking soda and potassium bicarbonate fungicides change leaf pH, inhibiting fungal growth and spore germination. Safe for many edibles.

Horticultural oils – Light oils smother fungal growth and spore production. Use only on woody plants. Avoid treating water-stressed plants.

Neem oil – Disrupts fungal cell structure and metabolism. Most effective as preventative. Can harm bee pollinators.

Biofungicides – Bacillus subtilis and other beneficial bacteria colonize leaf surfaces, blocking access to mildew fungi.

Synthetic fungicides – Products containing trifloxystrobin, myclobutanil, propiconazole, chlorothalonil or copper are effective but may damage bee pollinators. Avoid using the same chemical class repeatedly.

For severe powdery mildew infection, especially on edible crops, synthetic fungicides properly applied by a licensed applicator according to label directions may offer the best disease control.

Control Powdery Mildew by Plant

Powdery mildew affects diverse plant species. Effective control requires an understanding of the growth habits and cultural requirements of affected plants. Tailor control strategies to the specific plant and situation. Here are some examples:

Controlling Powdery Mildew on Roses

Choose resistant rose varieties. Space plants far enough apart for good air movement. Water at the base, avoid wetting foliage. Apply mulch to cool soil and reduce water needs. Remove diseased canes. Apply registered fungicides weekly as needed during disease prone times. Neem oil or bicarbonates may provide adequate control in home gardens. Monitor and treat early before mildew spreads.

Stopping Powdery Mildew on Monarda

Scout bee balm plantings weekly. At first sign of powdery mildew, prune out affected stems and leaves. Disinfect tools between cuts. Space plants adequately and avoid excess nitrogen. Apply mulch to cool soil and reduce frequency of watering. Use fans to improve airflow if mildew pressure is high. Apply biofungicides or bicarbonates weekly as a protectant during disease prone periods. Remove and destroy all vegetation in fall.

Preventing Powdery Mildew on Squash

Plant mildew resistant squash varieties. Promote air circulation by proper spacing, pruning and selective staking. Apply fungicides weekly preventively once vines start to run. Rotate synthetic fungicides to avoid resistance. Organic options such as neem oil, sulfur or biofungicides can help minimize use of synthetics. Promptly remove and bury or burn badly infected fruits and vines. Fall clean up of debris is essential for disease control.

Controlling Powdery Mildew on Apple Trees

Choose resistant varieties where possible. Prune trees for good airflow. Avoid excessive nitrogen fertilization. Scout trees weekly and remove infected shoots promptly. Apply registered fungicide spray to protect emerging leaves and fruit. Ensure thorough coverage. Repeat applications on a 7-14 day schedule depending on product label directions. Tank mixes combining synthetic and biofungicides may enhance control.

Stopping Powdery Mildew on Herbs

Plant in well-drained soil in full sun. Space plants properly and prune back neighboring plants encroaching on herbs. Avoid overhead watering. Apply mulch. Monitor plants closely and remove affected leaves or stems promptly. Spray with neem oil weekly as preventative if mildew prone. Potted herbs can be moved into protected locations during disease favorable weather. Grow resistant varieties of sage, bee balm or phlox. Discard severely infected plants.

Common Questions about Controlling Powdery Mildew

How do you get rid of powdery mildew naturally?

Natural methods to control powdery mildew include choosing resistant varieties, following good sanitation practices, providing proper plant spacing and air circulation, avoiding excess irrigation and fertilization, applying mulch, using fans to improve air flow and applying least-toxic fungicides like neem oil, sulfur, bicarbonates or biofungicides.

What is the best homemade spray for powdery mildew?

Effective homemade sprays for powdery mildew include:

• Baking soda – 1-2 teaspoons baking soda + 1 quart water. Spray leaves weekly.
• Milk – 40% milk 60% water. Spray leaves weekly.
• Neem oil – Follow label rates. Spray as preventative.
• Sulfur – 5 tablespoons wettable powdered sulfur per gallon water. Do not apply when temperature will exceed 85°F.

How do you get rid of powdery mildew on indoor plants?

To control powdery mildew on houseplants, isolate affected plants. Improve air circulation with fans. Prune back infected leaves and stems. Apply neem oil or biofungicide sprays weekly. Reduce watering frequency. Discard severely infected plants. For valuable plants, synthetic fungicides applied by a licensed applicator may offer best control.

Does vinegar get rid of powdery mildew?

Vinegar may help control powdery mildew. Spray plants weekly with a solution of 1 part vinegar mixed with 2 parts water. The vinegar changes the pH on leaf surfaces which inhibits fungal growth and spore germination. However, vinegar may also burn and damage plant tissues. Test on a small area first.

How do you treat powdery mildew without chemicals?

Non-chemical methods to treat powdery mildew include pruning infected plant parts, spacing plants properly to improve air circulation, using fans to improve airflow, applying mulch to cool soil, watering early in the day, choosing resistant varieties, applying neem oil, sulfur, or bicarbonate sprays, and discarding severely infected plants.

Conclusion

Powdery mildew is a common disease affecting many garden crops and ornamental plants. While rarely fatal, it can seriously mar plant appearance and vigor. A two-pronged approach is required to successfully manage this fungal disease. First, utilize cultural practices that promote plant health and discourage fungal growth. Second, apply least toxic fungicides preventively during periods of high disease risk. With diligence and prompt attention, powdery mildew can be controlled and its impacts minimized in home and commercial plantings. The reward will be healthy, productive plants and bountiful harvests.

How to Stop Powdery Mildew on Leaves

Powdery mildew is a troublesome fungal disease that affects a wide variety of plants. Thankfully, with a good understanding of what causes powdery mildew and using integrated pest management techniques, you can successfully prevent and treat powdery mildew infections. Here is a comprehensive overview on how to stop powdery mildew on leaves so you can keep your plants healthy and thriving.

What is Powdery Mildew?

Powdery mildew is caused by various fungal species in the order Erysiphales. These fungi thrive in warm, humid environments.

Powdery mildew gets its name from the white to gray powdery spots and patches that form on the surface of leaves, stems, flowers and fruits of infected plants. These powdery areas are made up of fungal mycelia and spores.

While not typically fatal to plants, powdery mildew can weaken plants, reduce growth and severely impact the quantity and quality of flowers and harvests. Powdery mildew fungi are very host specific, so mildews that attack rose will not infect bean plants and vice versa.

Conditions that Favor Powdery Mildew

Powdery mildew fungi need living plant tissue to grow. Specific environmental conditions trigger the onset of infections:

• High humidity – prolonged wet foliage encourages spore germination and infection
• Moderate temperatures – between 60-80°F
• Still air – poor air circulation allows fungal spores to linger on plant surfaces
• Shady conditions – powdery mildews thrive in shade
• Lush growth – succulent plant tissues are very susceptible
• Stressed plants – drought, poor nutrition, etc. increase vulnerability

By understanding what conditions promote powdery mildew, steps can be taken to discourage fungal growth.

Preventing Powdery Mildew Infections

Prevention is the first line of defense against powdery mildew. Here are effective cultural practices to avoid mildew problems:

• Choose resistant varieties – look for PM resistant cultivars
• Space plants properly – allow good air circulation
• Avoid excessive nitrogen fertilization – promotes soft growth
• Prune selectively – improve airflow by thinning dense growth
• Water early in the day – allow leaves to dry before night
• Use drip irrigation – avoids wetting foliage
• Apply mulch – cools soil and reduces water needs
• Monitor regularly – early detection allows prompt treatment
• Remove infected plant parts – protect healthy tissue
• Clean up debris – removes spore source
• Minimize plant stress – promote vigor through proper care

Implementing these practices provides an integrated approach to powdery mildew management.

Chemical Control Options

When cultural methods fail to prevent powdery mildew, fungicide applications provide another level of defense. There are effective organic and synthetic fungicide products.

Organic fungicides

• Sulfur
• Neem oil
• Potassium bicarbonate
• Bacillus subtilis
• Horticultural oils

Synthetic fungicides

• Triforine
• Myclobutanil
• Fenarimol
• Propiconazole
• Azoxystrobin

Treatment is most effective when applied at the first signs of mildew. Spray all plant surfaces thoroughly. Reapply every 7-14 days as needed during disease prone times.Rotate chemicals from different classes to manage resistance issues. Follow all label directions carefully.

Powdery Mildew Management by Plant

The strategies for controlling powdery mildew may vary depending on the plant infected. Here are some examples:

Roses – Choose resistant varieties, prune for airflow, apply registered fungicides preventively, discard badly infected canes.

Bee Balm – Space plants properly, monitor weekly, remove affected foliage promptly, apply neem oil preventively.

Melons – Use resistant varieties, promote airflow, apply fungicides weekly when vines start to run.

Grapes – Train vines for air circulation, limit nitrogen, apply sulfur preventively, discard severely infected fruit.

Squash – Plant resistant varieties, increase spacing, apply fungicides weekly, destroy debris promptly.

Apple Trees – Select resistant cultivars, scout regularly, prune for airflow, apply registered fungicide program.

Common Powdery Mildew Questions

What home remedy kills powdery mildew?

Effective homemade powdery mildew treatments include baking soda spray (1-2 teaspoons per quart water), milk spray (40% milk/60% water), or neem oil foliar spray (follow label rates). Apply to all plant surfaces weekly.

How do you get rid of powdery mildew on plants naturally?

Natural ways to combat powdery mildew include choosing resistant varieties, proper spacing for airflow, pruning infected parts promptly, applying mulch, watering at base of plants, using fans for airflow, discarding diseased debris, and spraying with neem oil, potassium bicarbonate or sulfur.

Is powdery mildew harmful to humans?

Powdery mildew fungi that attack plants do not infect or cause health issues in humans. The fungal spores may cause mild respiratory irritation in some people if inhaled in large amounts. Overall, powdery mildew is not considered a human health hazard.

What month is powdery mildew worst?

Powdery mildew problems tend to peak in late summer to early fall when nighttime temperatures are cool and daytime temperatures are warm. Shady, humid conditions also favor powdery mildew during this time. Stay vigilant for mildew development in August through October.

Does powdery mildew mean bad soil?

Powdery mildew is not caused by poor soil conditions. This fungal disease is triggered by specific climate conditions, susceptible varieties, shady sites, lush growth, poor air circulation, planting stress, etc. Proper soil nutrition is important to grow healthy plants that can better withstand powdery mildew pressure.

How do you treat powdery mildew without chemicals?

Non-chemical methods of treating powdery mildew include: pruning affected parts, planting resistant varieties, spacing plants properly, applying mulch, using fans for airflow, removing plant debris promptly, applying neem oil or baking soda spray, and discarding badly infected plants.

Conclusion

Powdery mildew can be frustrating for gardeners. However, by understanding what conditions trigger powdery mildew fungi, and utilizing an integrated disease management approach, you can successfully prevent and treat infections. Start with good cultural practices to keep plants healthy and less susceptible. Monitor regularly and treat early. Use organic or synthetic fungicides properly when conditions favor disease. With knowledge and persistence, you can protect your plants from destructive powdery mildew.

How to Stop Powdery Mildew on Leaves

Powdery mildew is a common fungal disease that affects a wide variety of plants. It can be frustrating for gardeners and farmers who find their plants disfigured by white powdery spots and patches. Thankfully, powdery mildew can be effectively controlled with some knowledge about the disease and by using integrated pest management techniques. Here is a comprehensive guide on how to prevent, treat and stop powdery mildew from damaging your plants.

What Causes Powdery Mildew?

Powdery mildew is caused by various species of fungi in