Chemical Remedies
Baking Soda
Examples:
One commercial product, Bonide Remedy, contains potassium bicarbonate, similar to baking soda. Or you can make your own (see recipe under "How to Use."
Effective Against:
Powdery mildew. May also help control black spot.
Crops:
Roses and other susceptible flowers.
Counteracts these pest(s):
How To Use
Mix one teaspoon of baking soda and one quart of water in a spray bottle. Add a few drops of dishwashing liquid. (Adding 1/2 teaspoon of oil, such as Sunspray Dormant Oil, may increase the effectiveness against black spot and other fungal diseases.) Apply this mixture to plants as needed.
For roses, begin applications right after pruning. Repeat once a week if needed. For other plants, apply when mildew is visible. On some annual plants, such as peas, squash, and annual flowers, mildew develops but is not a threat to the plant because it occurs late in the season. Destroy, do not compost, affected leaves when plant is ready to be removed.
Benefits
Non-toxic. Highly effective on powdery mildew.
Concerns
Less effective on other fungal diseases.
Alternate Method
Fungal diseases should also be prevented by removing and destroying affected leaves that fall to the ground and, by watering at the base rather than overhead. On roses, remove leaves that form within about a foot of the ground, where splashing rain spreads disease. Consider planting disease-resistant varieties.