Rose rust disease has been showing up on 'knock out' roses lately.  This fungus is a common infection in roses. Rose rust is a disease that causes orange-colored spots to appear on the leaves and stems.

When the rust fungus infection is severe, an orange dusty substance may be present on the plant tissue and on the ground surface below the plant. This dusty substance is fungal spores. Rose rust attacks all plant parts except the roots and petals. Severely infected leaves of rose plants may turn yellow or brown and drop.

To prevent rust infection provide good air circulation. Do not plant roses too close together. Prune bushy rose plants to keep the centers open. Water plants before in the morning. Do not get the leaves wet. Remove and destroy diseased leaves. Sometimes plants that are too susceptible should be removed.

To preventatively treat roses, use fungicides containing myclobutanil, mancozeb, or propiconazole. Apply all chemicals according to directions on the label.