Powdery mildew is a fungus! It grows in cool, damp environments.
You must grow hardy, disease resistant strains and create ideal growing conditions for your plants!
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Integrated Pest Management (IPM)
Powdery mildew thrives where large amounts of nitrogen have been used on plants.
This fungus develops quickly under favorable conditions because the length of time between infection and the appearance of symptoms is usually only three to seven (3-7) days and a large number of conidia can be produced in a short time.
Dense plant growth, low light intensity. High relative humidity (RH) is favorable for infection and conidial survival, infection can take place at RH levels as low as fifty (50%) percent.
Dry conditions are favorable for colonization, sporulation and dispersal. Rain and free moisture on plant surfaces are unfavorable, however, disease development occurs in both the presence or absence of dew (water). Infection can occur from fifty to ninety (50-90) degrees F.; mean temperatures of sixty eight to eighty (68-80) degrees F. are favorable. Powdery mildew development is arrested at daytime temperatures of one hundred (100) degrees F. or higher. Plants in the field are often not affected until after fruit initiation. The leaves are most susceptible sixteen to twenty three (16-23) days after unfolding.
Contrary to popular belief, powdery mildew does not require free water to establish and grow. Infection can occur on dry leaves. Warm temperatures and shady conditions encourage the fungus to grow and spread. However, the spores and mycelium (roots) are sensitive to extreme heat and direct sunlight.
The optimum temperature for infection is between sixty eight to seventy seven (68-77) degrees F. and relative humidity between forty to one hundred (40-100) percent is sufficient for the spores to germinate. Low, diffuse light also seems to favor powdery mildew development. The mildew can spread rapidly since the disease cycle can be completed in as little as seventy two (72) hours. However, it commonly takes seven to ten (7-10) days from the time of infection to the development of symptoms and secondary spore production.
Powdery mildew thrives where high rates of nitrogen have been used. High nitrogen promotes tender leaf formation, causing dense stands (leaves) that are more suspetible to infections. Adequately fertilize but avoid stimulating succulent growth. Organic fertilizers or slow release fertilizers are best.
Prune out infected plant parts to increase airflow. If infestations are severe, remove and destroy infected plants. Disinfect pruning equipment in a bleach solution: 1 part bleach (clorox) to 4 parts water after each cut!
Do not crowd plants! Ventilation will discourage mildew growth. Water plants in the morning--they have all day to dry off!
Sulfur is highly effective against powdery mildew. Seven to fourteen (7-14) days between applications.
Garlic (high sulfur levels) and water spray. Crush or use blender four to five (4-5) cloves of garlic. Add to one (1) gallon spring water.
Baking Soda Spray-
1 teaspoon baking soda
1 quart water
2-3 drops liquid soap (surfactant) helps spray to stick to leaves (top and underside)
2-3 drops vegetable oil (olive, canola) helps contain spores
Put in spray bottle, shake well and spray plants every four to five (4-5) days. Spray both sides of leaves. You must use proper timing when applying fungicides--it is critical.
Why baking soda solution works? This solution changes the pH balance on the surface of the leaves, making the environment unsuitable for the fungus, Powdery Mildew, to proliferate.
Product called "Serenade"--organic. Good to cure powdery mildew and Botrytis.
Use good Integrated Pest Management (IPM) methods.