Common Rose Diseases and their Prevention
There are many factors that come into play when spinning the roulette wheel of rose diseases in your garden. Some years you may not have much of a problem with blackspot, rust and mildew and the next you struggle all season to rid you garden of these nuisances. Let’s briefly examine our opposition and our plan of attack.
Blackspot – Appropriately named for the dark-colored spots that appear on leaves. As the disease progresses the leaves turn yellow and fall off the plant. Blackspot often appears in humid areas or later in the summer in area know for July and August thunder showers.
Leaves exhibiting evidence of blackspot should be removed (remember to clean up any leaves that fall around the base of the plan). You man need to cut back areas of the plant.
Mildew – Powdery mildew appears as a whitish powder on the leaves and stems of the plant. Left untreated it will spread along the canes. Powdery mildew is common to areas with warm summer days but cool and damp nights.
Mildew can be treated with a fungicide spray. Thin out congested areas of the plant to increase air circulation. Clean around the base of the affected plants as well.
Rust – Another aptly named disease, rust shows up as orange spots on the underside of leaves. Rust can spread throughout a plant, defoliating the leaves and possibly killing the rose.
Although rust can be treated by some sprays, not all will be effective. Remove effected leaves and areas of the plant. Thin canes as well to promote better air circulation within the plant. Rust appears on plants in humid or damp areas so if you are watering with sprinklers you may want to check into other method that doesn’t leave the upper part of the bush wet.
Although you can’t do much about a damp climate you can check to see if you are watering the leaves instead of the roots. Although roses like water they need soaking at the base not in the areas prone to disease.
Natural Disease Resistance
Recent All-America Rose Selections (AARS) winners Julia Child, Strike it Rich, Memorial Day, Livin' Easy, Hot Cocoa and About Face are all examples of stunningly beautiful roses with a natural resistance to disease.
If you have one or more older roses that repeat the disease cycle each year you may want to consider some “shovel pruning” and replacing them with new, more disease resistant varieties such as Home Run.