Prevention is key to managing this widespread plant disease.
Even some turf grasses are susceptible to powdery mildew.
Gardeners find infected plants unsightly, and severe infections can cause foliage to turn yellow and drop prematurely.
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Powdery mildew is difficult to control once plants are infected.
Powdery mildew appears as white to gray spots or patches on leaves, stems, fruits, or flowers.
The spots have a powdery-looking appearance, giving the disease complex itsname.
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These patches grow and spread over plant surfaces and produce root-like structures that penetrate plant cells to extract nutrients.
As the disease progresses, plant growth may be stunted and infected plant parts become distorted.
Severe infections can lead to premature leaf drop, reduced flowering, and smaller yields.
The right environmental conditions must exist for infection to occur.
Although these fungi thrive in hot, dry conditions, they do require high humidity for spore germination.
Warm and humid spring weather favors infection.
Succulent plant tissues are more susceptible to infection, including new growth of young plants.
This is accomplished through adequate plant spacing and selective pruning.
Avoid overcrowding plants, particularly in sheltered locations.
Use the expected mature size as a spacing guide when installing new plants.
Dense hedges can also be pruned to enhance air circulation in adjacent planting beds.
Stake herbaceous plants as needed and remove weeds to keep the air moving.
Sterilize garden tools after pruning infected plants to prevent spore transfer to healthy plants.
Another way to reduce humidity in the plant canopy is by watering through drip irrigation or soaker hoses.
This keeps moisture at the ground level, where it is needed.
Be judicious with fertilizer.
Excess nitrogen encourages plants to produce new growth, which is more susceptible to infection.
Environmental conditions are just one part of the diseases cycle.
Powder mildew spores must also encounter a susceptible host for disease to develop.
Planting mildew-resistant cultivars is a great way to stop the disease cycle.
Resistant varieties are available for roses, turfgrasses, andmany shrubs, flowers, and fruit and vegetable crops.
Finally, it is important to practice good sanitation to reduce return infections from one year to the next.
Likewise, rake and dispose of fallen leaves from infected trees and shrubs.
Burn infected plant material or dispose of it in a closed container.
Do not add infected plant material to the compost pile.
Likewise, gardeners may choose to treat valuable species.
Both organic and inorganic fungicides can be used to treat powdery mildew.
These are most effective when combined with the cultural controls described above.
When using fungicides, timing is critical.
Inspect susceptible plants weekly for signs of infection.
When the first white spot appears, pinch off the infected foliage and begin fungicide applications.
The fungicide must thoroughly cover all plant tissues to prevent disease.
Neem and other horticultural oils are well-known organic pesticides used to manage plant diseases and insect pests.
Some plants do not tolerate sulfur applications.
Check product labels to be sure the plant you wish to treat is labeled for the product.
Milk sprays have shown promise in vegetable crops, but little is known about their use on ornamental plants.
As for baking soda, the greatest success was observed when mixing diluted baking soda with horticulture oil.
Powdery mildew does not significantly affect plant health and treatment is seldom needed, particularly on long lived species.
Powdery mildew fungi are host-specific, meaning each fungal species only infects specific plant species.
Cross infection is more likely among closely related plant species, such as cucumber and squash.
