Q: I just read about rose rosette disease. Can we spray our Knockout roses with Volck oil spray in trying to keep the mites that spread this disease at bay?
A: Rose rosette affects all roses. The most common symptoms are distinct short red stems at the end of canes and huge numbers of thorns nearby. The disease is spread by tiny mites. The female mites hide in bark cracks in winter and lay their eggs in early spring.
Horticultural oil sprays will keep numbers under control but they should start before budbreak (usually February), with a spray at budbreak (usually March) and repeat sprays every two weeks.
Since the mites and the disease are by no means wide spread, it is possible all of your work could be a waste of time. If your roses (or neighbor roses) don’t exhibit symptoms there’s no need to do anything.
If the symptoms are found, the plant should be removed. Pruning will not control the disease.
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