White Fuzzy Growth on Parade Roses

Fungal Organism

• The first recorded case of powdery mildew appears in literature around 300 B.C. Sphaerotheca pannosa, the fungus that causes powdery mildew, is very difficult to control due to its short 72-hour lifecycle. If left unchecked, powdery mildew quickly becomes a serious problem. Cool, damp nights followed by dry, warm days create the ideal conditions for powdery mildew growth.

Symptoms

• Roses infected with powdery mildew exhibit vague symptoms, such as distortion and dwarfing of new shoots. However, the powdery or fuzzy white coating that covers unfolding and expanding leaves is unmistakable. Severe infection cause mildew-coated, curled or twisted leaves that eventually turn purple, then yellow or brown, and drop. An entire plant’s death is rare, although powdery mildew significantly damages flowers and fruits.

Treatment

• Treat powdery mildew with a horticultural fungicide as soon as it appears. Fungicides labeled to control both black spot and powdery mildew are recommended, since the two fungi grow under similar conditions. Recommended fungicides include the copper fungicides, propiconazole, thiophanate-methyl, triadimefon, triforine, sulfur or neem oil. Always apply fungicides according to label directions.

Prevention

• Planting resistant rose varieties best prevents powdery mildew. Miniature roses are not currently among those with high powdery mildew resistance, but new cultivars are in constant development. In the meantime, provide miniature roses with good air circulation and full sun exposure. Clean up any fallen debris and prune infected sections. Water the roses regularly from the bottom of the plant, but fertilize only when necessary.