Avoid wounding canes. Cankers often develop after cold temperature injury, so early spring pruning may not effectively eliminate them when late frosts occur, and additional late spring pruning may be necessary. Winter injury from cold temperature results in dead or dying flowers, twigs, and stems. Roses may be protected over the winter with a thick layer of leaf mulch in cold mountain areas. Winter injury may be followed by stem canker diseases caused by pathogens that move into injured tissue.
Sunburn appears as blackened areas, especially on the south and west sides of canes.
Sunburn is caused by excessive temperatures on rose canes usually as an indirect result of defoliation caused by drought stress or spider mite pressure. Reflected heat from masonry, vinyl siding, or rock mulch may also cause canes to sunburn. Crown gall , caused by the bacterium Agrobacterium tumefaciens, affects many woody plants including fruit trees, ornamentals, and roses as well as some herbaceous plants including chrysanthemums and daisies. Crown gall bacteria invade tissue after wounding. Galls, in the form of large, distorted tissue growth, form at the base of the cane or sometimes on roots or farther up on stems.