Powdery mildew is one of the most common fungal issues afflicting home gardeners and farmers alike. Its symptoms are easily spotted; however, it can spread to the point of being out of control quickly. The term "powdery mildew" encompasses a range of related fungal species which all possess similar symptoms , but each target specific hosts. Beans, cucumbers, roses, tomatoes and zucchini are highly susceptible to powdery mildew infection. Thankfully, all variations of powdery mildew are easily distinguishable from other fungal diseases, generally not fatal to the plant and have many treatments available to choose from.
Identification & Appearance:
Chances are good that you have seen powdery mildew before, but you may not have needed to take action. Commonly found on upper leaf surfaces, the most identifiable features of powdery mildew are the white or gray spots covering parts of or the whole leaf surface. Damage to the plant is usually minimal, but severe issues can result in leaves browning and eventually dropping. New growth is particularly affected by mildew issues. Inspection of the whole plant is recommended to catch mold and mildew issues early on.
While most pathogenic fungi require water to infect hosts, powdery mildew is unique in that it does not. Shaded areas and dense plantings are hot spot areas for powdery mildew to grow and spread.
Controlling Powdery Mildew:
Early identification and action are the best treatment for powdery mildew. Below are a few control measures to take when dealing with powdery mildew:
Cultural & Physical Controls for Prevention/Maintenance
- Avoid overhead watering as an overly damp environment increases powdery mildew spore germination.
- Remove dead plant material and debris to reduce overwintering and cultivation sites. Powdery mildew spores are excellent survivors and will overwinter within plant tissue as well as in cracks and crevices that are hard to reach.
- Plant resistant varieties when possible.
- Clean the growing environment (greenhouse, grow room, cold frame, etc.) and any tools you use thoroughly before planting/use. Sanidate, BioSafe Disease Control and OxiDate are great for cleaning tools and enclosed growing areas.
- Remove affected foliage, if needed, and any already fallen leaves. Do not compost plant debris that has powdery mildew.
Biological & Chemical Controls for Treatment
- Bacillus subtilis products should be used preventively for best results. Limit incidence of fungal diseases on foliage with these biofungicides.
- Sulfur (Bonide Sulfur Plant Fungicide) and copper fungicides (BONIDE Copper Fungicide Dust) can prevent powdery mildew issues and control existing fungal problems.
- Rinse foliage with SuffOil-X on a regular spray schedule for continued control of powdery mildew issues. Use caution in high heat and under bright lighting to prevent burning.
- Apply Monterey Bi-Carb Fungicide or Monterey Complete Disease Control to plants already afflicted. Both can also be used as preventive measures when used on a regular schedule.
- Use MilStop for large-scale applications.