Things You'll Need
Clean, sharp shears
Plastic container with lid
Liquid castile soap or non-degreasing liquid dish soap
Plastic spray bottle
Your Gerbera daisy (Gerbera Jamesonii) may succumb to powdery mildew when the weather cools near the end of the growing season. This infection can be caused by various fungi that thrive in damp conditions and spread their spores easily through air currents and splashing water droplets. While numerous chemical preparations for powdery mildew are readily available, the combination of sound cultural practices and homemade canola oil fungicide may deliver even better results. Fungi don't build up resistance to oil fungicides as they quickly do with chemical preparations. This means that you can cure the Gerbera's fungus without the hassle or expense of repeatedly switching dangerous synthetic treatments. Hardy in U.S. Department of Agriculture plant hardiness zones 9 to 11, these colorful daisies are commonly grown as annuals in colder regions.
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Inspect your Gerbera daisy's flowers, leaves, stems and shoots daily for signs of powdery mildew, especially during the cooler months of fall and winter. Look carefully for powdery white patches or spots on all the plant's surfaces. Foliage eventually yellows or turns brown and dies. This fungal infection typically reduces growth, so the plant may appear stunted like it's in poor health in general.
Isolate the infected Gerbera from all of your other plants immediately to prevent the spread of the disease to healthy specimens. After a few months of diligent treatment, you should be able to return the sick Gerbera to its former happy home.
Hand pick all infected parts off the plant as soon as you see any white spots. Use clean, sharp shears to prune some of the stems from the center of the plant if it's extremely full. This encourages good air circulation, which powdery mildew isn't fond of. Put all the infected clippings in a plastic bag and tie it tightly shut. Dispose of the bag in the trash. Don't add sick foliage to your compost pile.
Add 1 cup of canola oil to a plastic container. Pour in 1 tablespoon of liquid castile soap or non-degreasing liquid dish soap to make a horticultural oil concentrate. Cap the lid firmly and shake the container briskly to blend the soap and oil. Write the formula clearly on the container with permanent marker. Store the oil concentrate in a dark, cool spot indefinitely.
Stir 1½ teaspoons of baking soda into 1 cup of very hot water. Stir until the baking soda is completely dissolved. Pour the solution into a plastic spray bottle. Add 1½ teaspoons of the oil concentrate. Shake vigorously to blend thoroughly. Use the mixture right away.
Spray the oil mixture generously on all surfaces of the Gerbera daisy to coat them to the point of runoff. Pay special attention to the undersides of the leaves, which tend to be overlooked. Agitate the sprayer after several spritzes to prevent the oil from separating from the water. The best time to treat powdery mildew is on a day when temperatures don't exceed 85 degrees Fahrenheit, there's no breeze and no precipitation is in the forecast. Discard any unused solution. Repeat the application every four to six days for the rest of the growing season.
Keep the Gerbera daisy's foliage as dry as possible. Powdery mildew spreads and grows quickly on plant surfaces that remain moist for long periods of time. Don't splash water on the plant's foliage as this speeds and strengthens the spread of the fungus. Don't mist the infected plant for the remainder of the season.
Locate the Gerbera in a warm spot, preferably above 75 degrees. Space multiple plants as far apart as possible to increase the airflow. Provide all the bright sunlight possible. Poor air circulation, inadequate light and temperatures close to or below 70 F promote powdery mildew growth.
The Environmental Protection Agency approves canola oil for pest and disease control in plants.
Wash your hands and sterilize your utensils right after you handle the infected Gerbera. This helps minimize the chances of spreading the fungus from plant to plant.
Test the spray solution on a small spot of the Gerbera before you apply it to the entire plant. If there is no sign of injury after two or three days, you can be sure it’s safe to use to treat the daisy for powdery mildew.
- University of Florida IFAS Extension: Powdery Mildew of Gerbera Daisy
- Floridata: Gerbera Jamesonii
- Organic Gardening: Powdery Mildew -- Steps to Prevention
- Clemson University Cooperative Extension: Common Houseplant Insects & Related Pests
- University of Florida IFAS St. Lucie County Extension: Home Remedies for Insect and Disease Control on Plants
- University of California: Powdery Mildew on Ornamentals
- The Complete Guide to Keeping Your Houseplants Alive and Thriving: Fungal Diseases
- Sierra Club of Canada: Pest Control Spray You Can Make in Your Kitchen!