How to Treat Canker in Roses

Inspect your roses weekly for areas of brown or black tissue encircling the canes. Symptoms take from four to 15 days to surface after infection. Wear gloves to protect your hands from thorns. Reduce the risk of spreading canker spores by examining the roses when they're completely dry.

Mix a bleach/water solution with a ratio of 1 part bleach to 9 parts water. Pour it into a glass or plastic container, because chlorine corrodes metal. Bring the solution with you when you treat your roses.

Use pruning shears to cut at least 2 inches below cankered canes to green, fungus-free branches.

Squeeze a drop of wood glue onto the cut end of each cane immediately after you prune it. This waterproof seal prevents stem borers from burrowing into and eating the canes' pulp.

Wipe your pruning shears with a towel or rag dipped in bleach solution between each cut. This prevents accidental spread of the fungus from diseased to healthy tissue.

Place all the cankered canes and other debris from the infected bushes into a plastic trash bag for disposal away from your rose bed. The fungus-bearing materials aren't suitable for composting.

Examine the roses’ healthy canes, and cut back any that rub against each other. Friction wounds invite canker infestation. Crossed canes also limit air circulation, encouraging stem moisture buildup. Cut back to 1/4 inch above a stem junction or five-leaflet leaf, where new growth sprouts.

Spray your actively growing roses every week or 10 days with a fungicide labeled to treat canker. Saturate all visible surfaces, including the leaves' undersides. In prolonged wet weather, spray on a five-day schedule before the rain starts. Post-rain spraying doesn’t protect the canes from water-borne fungal spores.