Organic Rose Gardening and Fungus Diseases

FUNGUS AND DISEASE ON ROSES
Blackspot and powdery mildew are two fungus diseases that develop when weather conditions are right-hot and humid weather after summer showers. Blackspot, caused by the fungus Diplocarpon rosae, begins as black spots on the leaves, and as it progresses, more spots develop and the leaves turn yellow and drop to the ground. Powdery mildew is caused by several types of fungi. It appears as grayish or whitish dusty-looking spots on leaves that spread to cover the entire leaf surface. Both of these diseases can cause complete defoliation if left unchecked. They weaken the plants, prevent flowering and make the plants unsightly.

Remove infected leaves as soon as you see them. Simply pick them off and dispose of them away from the garden. Black spot and powdery mildew usually don't kill roses, but the defoliation makes photosynthesis and normal plant processes impossible until new foliage grows. The disease spores remain in the ground from previous infections from year to year. Keep dropped leaves cleaned up, and burn them or put them in the trash. Never put diseased leaves or clippings in a compost pile or use them as mulch, because the spores will reinfect the soil. I like to replace the mulch around my roses with fresh material in the spring and again in the fall. It may seem that mulch harbors the spores, but it actually can serve as a barrier between the infected soil and the rose foliage. Rain on bare ground can cause splashing that moves the spores from the soil directly onto the rose leaves, and a layer of mulch helps prevent this.

Another common rose disease is rust, caused by the fungus, Phragmidium sp. It begins as rusty-colored spots on the underside of the leaves. Infected parts of the plant turn an orange-rust color; leaves usually curl and become deformed before defoliation occurs. It also affects the canes, and can kill the plant if left untreated. Remove and destroy affected leaves and canes, and use fungicide to control severe rust infections. See rust images here.

Use a commercial organic fungicide spray if your fungus problem is severe. Look for sulfur as a fungicidal ingredient, or buy sulfur at your garden center and use it in your own organic treatment program. I spray the ground around the rose bushes as well as the plants. When you buy rose plants, look for disease resistant varieties.

Try to defend your roses against a fungus attack before it gets out of hand.

This home remedy fungicide spray works for mild fungus problems:

ONE Gallon Water
2 teaspoons baking soda
1 Tablespoon Neem Oil or light carrier oil, such as almond oil or grapeseed oil
1/2 teaspoon insecticidal soap or Ivory Liquid dish soap as a dispersant
(don't use heavy de-greaser dish detergents or dish detergents with bleach or anti-bacterial chemicals added)

Water the rose plants deeply the day before you spray. The plants must not be dehydrated. Spray early in the morning so the leaves have time to dry thoroughly before evening dew. Spray tops and undersides of the leaves. Keep the liquid well mixed as you spray by shaking or swirling the sprayer tank.

Click here for information about caring for your roses in the summer heat.

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Source:
Personal Experience