Fungus on Iceberg Roses

Fungus Prevention

• Plant roses in full sun with plenty of air circulation around them. Amend the soil with rich compost and manure when planting and water them weekly at the base, not above. Avoid wetting the foliage, as this encourages fungal disease. Mulching the planting area with bark chips or compost keeps the moisture level even and weeds at bay. Keep the area under roses clean of fallen leaves and prunings. Discourage fungus diseases on Iceberg roses by spraying fungicide as the first leaves emerge in spring. Use an organic product containing sulfur or copper, or a synthetic fungicide. Once a fungus starts, cut off and destroy infected plant parts. Continue spraying to keep the disease from spreading to healthy tissue.

Mildew and Rust

• Mildew is a fuzzy gray or white growth on leaves or buds resembling mold. It causes young leaves to curl up, turn purple and drop off. Affected buds don't open, just decay. Mildew spreads on the wind and develops quickly during wet or humid weather. Rust, another fungal disease, thrives in cool, wet weather and spreads by wind and water. Powdery orange lesions on plant leaves and stems characterize it.

Blackspot

• Blackspot is a fungus long associated with roses, although it also attacks other plants. Distinctive round, black spots on leaves and stems, sometimes with a yellow halo are its symptoms. Leaves die and fall off, while stems blacken and die. Leaf cleanup mitigates blackspot. Pick off any diseased leaves and cut off diseased stems, wiping your pruner with bleach after each cut. Blackspot spreads by water, so water the rose only at its base. After removing the diseased plant parts, begin spraying with fungicide.

Botrytis

• Botrytis turns buds and stems dark brown, and then black. They shrivel, droop and die. Gray fuzz often covers unopened buds affected by botrytis. Flowers are affected with the entire bloom covered with gray mold. Botrytis spreads in rainy weather when leaves remain wet all day or if the rose is watered with a sprinkler. Cut off and dispose any diseased plant parts and begin spraying with fungicide.