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How to Control Powdery Mildew in Your YardBy: Julie Day
Powdery mildew happens to even the most carefully tended plants – seemingly out of nowhere, prized ornamental plants and lawns get a fuzzy gray coating that reminds you of that container you pulled out of the back of the fridge. Powdery mildew isn’t immediately fatal, but it can cause considerable stress to your plants. Fortunately, you can control it in a few easy steps, and here’s how.
About Powdery Mildew
The term “powdery mildew” actually refers to an entire group of fungi, each one attacking different types of plants. It usually starts with a few round white or grayish spots that you can rub off with your finger. They spread and join until the entire top leaf surface is covered, then it moves on to the underneath, stems, flowers, and fruit.
As powdery mildew takes over, photosynthesis becomes very difficult for the plant. This can cause growth of the plant to slow and distort, leaves to fall, and flowers and fruits to fail to form properly.
Powdery mildew can affect any plant, but lilacs, roses, fruit trees, vegetables, begonias, and lawns are particularly susceptible. Since the fungi are species specific, powdery mildew on your fruit trees won’t spread to camellias or other plants.
How to Treat Powdery Mildew
Powdery mildew may seem to spring up faster than you can control it, but the good news is that it’s easy to treat and not immediately fatal. Take these steps to treat powdery mildew on your plants:
- Prune: Cut off affected growth, prune the plant to open it up to more air circulation, and trim back tree limbs that might be shading too densely.
- Disinfect: Clean pruning tools in a bleach/water solution to kill any remaining spores.
- Clean Up: Pick up all fallen leaves and pruning debris and put either in the trash or in a hot compost pile.
- Stop Fertilizing: Reduce nitrogen fertilizer in order to slow down succulent growth.
- Spray with Water: If plants are in the sun, try washing the patches off the leaves with a spray of water. Avoid extra water in shady or damp areas.
- Spray with Fungicide: If all else fails, spray plants with an eradicating fungicide. Check the label to make sure it’s rated both for powdery mildew and for your plant type. Natural treatments include neem oil, copper, and potassium bicarbonate. Use chemical fungicides only as a last resort.
How to Prevent Powdery Mildew
Of course, the best way to treat any plant disease is to avoid it in the first place! Try these steps to keep powdery mildew from taking over your yard:
- Choose Resistant Plants: Some varieties of plants are more resistant than others – check the plant labels before you buy.
- Focus on Air Flow: When planning your garden, make sure that all areas have adequate air circulation and that plants are adequately spaced. Thin or prune plants and trees as necessary to prevent stagnant, humid corners.
- Grow in Sun: Whenever possible, orient your planting beds so they get at least a few hours of sun each day.
- Use Preventative: If powdery mildew is a problem in your yard, spray your plants with preventative fungicides to keep it at bay. Natural preventatives include sulfur and baking soda. For an easy homemade preventative spray, mix a spoonful of baking soda and a spoonful of either dish soap or horticultural oil (such as neem oil) into a gallon of water. Don’t overuse the spray – you don’t want to the baking soda to build up in your soil.
- Spray Regularly: Apply preventative sprays every couple of weeks.
- Vary Plantings: Since the fungus is species specific, reduce infection of your annual plants by rotating the varieties of plants each year.
- Water Wisely: Water in the morning to allow plants to dry. Use soaker hoses and drip irrigation, rather than overhead sprinklers, to reduce humidity around your plants.
- Don’t Overfeed: To keep growth in check, use balanced organic fertilizers and compost, rather than high-nitrogen chemical fertilizers.
- Powdery Mildew Fact Sheet (Cornell University)
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