Roses (Rosa spp.) make beautiful and fragrant additions to a garden, but sometimes prove difficult to grow. Many varieties are susceptible to fungal disease, which can make it a challenge to keep them looking their best. This is particularly true for organic gardeners, who can't just pop to the hardware store for a quick fix when fighting garden diseases and pests. The good news is that a homemade baking soda-based mixture makes a natural fungicide for rosebushes.
What You're Up Against
Roses can suffer from a wide variety of fungal diseases, but black spot fungus and powdery mildew are the most common in the United States. Downy mildew and botrytis blight are also fairly common.
As the name implies, black spot fungus on the leaves of your plant creates black spots with yellow borders. The disease can eventually cause leaf drop. Without adequate leaves for robust photosynthesis, the rosebush will produce fewer blooms and lose its overall vigor.
Like black spot, powdery mildew is easy to identify. It makes the entire plant appear dusted with flour. Botrytis blight is a bit more particular, tending to attack flowers and buds rather than the entire plant and coating its victims with a grayish-brown fuzz. Although it usually starts with the roses themselves, botrytis travels down the stems of the plant if left untreated.
Often misidentified as black spot fungus, downy mildew creates black, red or purple spots on rosebush leaves and works from the top of the plant down, while black spot moves up from the bottom. Black spot lesions can appear anywhere on a leaf, but patches of downy mildew stay between leaf veins.
Preventing the Problem
An ounce of prevention really is worth a pound of cure — particularly in an organic garden where harsh chemical fungicides are banned. Preventing fungal disease starts with disease-resistant cultivars: 'Eiffel Tower,' 'Matterhorn,' 'Carefree Wonder,' 'Saratoga' and 'Pink Parfait' all resist both powdery mildew and black spot disease.
It's also important to keep your garden clean. Prune away any dead or diseased canes on your roses as soon as you see them. Rake up fallen leaves and rose petals frequently. If you've had diseased leaves or flowers fall onto your mulch, rake it up at the end of the season and replace it with fresh mulch in the spring.
Note that, with the exception of powdery mildew, most fungi need a lot of water and moisture to thrive, so do your best to deprive them. Use soaker hoses to water your plants rather than watering from above, and, after a rain shower, stay away from your roses until they dry. Plant multiple rosebushes 3 to 4 feet apart so that air can easily circulate around them.
Natural Fungicide Recipe
Sometimes solutions to plant problems are simple. For example, you can often cure powdery mildew with nothing more than water. Spray the leaves of the plant with ice-cold water first thing in the morning so they have all day to dry. A few days of this is often enough to cure powdery mildew.
If this doesn't work — or if you're dealing with a different problem — you can turn to home remedies. Gardeners admittedly share some crazy remedies for garden problems, but there's some scientific evidence backing the use of baking soda as a fungicide when it's mixed with an oil. In fact, even the U.S. Department of Agriculture recommends a baking soda and oil mixture for natural fungal control.
To make a natural fungicide for your roses, add 4 teaspoons of baking soda, a teaspoon of cooking oil and a teaspoon of dish soap to a gallon of water. Mix the ingredients well and then transfer them to a spray bottle. Spray the leaves of your roses liberally with the mixture, remembering to spray the underside of the leaves as well. The plant should be dripping wet when you're done.
This concoction works well when applied weekly to plants as a fungal prevention. It also cures some fungal diseases, including powdery mildew. For continued protection, spray your plant with this mixture about once a week.
- Rose Magazine: Blackspot
- MIgardener: Prevent and Kill Blight & Powdery Mildew With Baking Soda
- Nursery Management: Rose Downy Mildew
- Clemson Cooperative Extension: Rose Diseases
- Heirloom Roses: Make Home Remedies for Pests and Diseases
- GrowNetwork: An Easy DIY Homemade Garden Fungicide
- American Rose Society: Fungicides Made Simple
- University of Vermont Extension: Horticutural Myths
- U.S. Department of Agriculture: Tomato Plant Diseases and How to Stop Them
Home is where the heart is, and Michelle frequently pens articles about ways to keep yours looking great and feeling cozy. Whether you want help organizing your closet, picking a paint color or finishing drywall, Michelle has you covered. If she's not puttering in the house, you'll find her in the garden playing in the dirt. Her garden articles provide tips and insight that anyone can use to turn a brown thumb green. You'll find her work on Modern Mom, The Nest and eHow as well as sprinkled throughout your other online home decor and improvement favorites.