Plant Doctor Archive

Fungus and mildew on roses

My roses have persistent mildew this year. I have tried several sprays including Bravo, Gild, Saprol and Shield. Some of the plants had it last year but I cannot get rid of it this year. Even my most healthy plants have it to a mild degree. I have cut the most severely affected back and sprayed. What winter care do I do to help prevent this problem next year?

Could you please tell me the cause and treatment for a white fungus that has appeared on my topiary rose? I have tried conventional rose spray to little effect. Could this be from watering using a sprinkler?

Because of the warm, humid weather we have been having, diseases have gone rampant. Once established, mildews are hard to control. Healthy plants have much more resistance to diseases, so regular feeding, watering, mulching and occasional spraying does help keep them at bay.

Clean up any fallen leaves, petals or prunings from around the roses to prevent diseases spreading.

The key to sprays being effective is spraying at regular 14 day intervals until the problem is under control and alternating sprays to prevent a build-up to resistance.

Spraying at regular 14 day intervals now will help prevent spores overwintering and affecting plants next season. Alternate with 2-3 sprays to prevent build-up to resistance. Greenguard, Fungus Fighter (which has superceded Bravo), and Saprol are all effective against mildews. There are also combination sprays, Guardall, Gild and Super Shield which control insect pests as well.

Ensure good air circulation around the plants, and try not to wet the foliage when watering. Avoid overhead watering to reduce the chance of mildews becoming a problem.

Spraying with Champion Copper through winter will help control black spot but not powdery mildew.

With improved rose breeding, there are more and more disease resistant varieties available now. When selecting new roses, keep an eye out for ones that state "disease resistant" on the label. Unfortunately, some varieties are susceptible to disease.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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