What Causes a Rosebush to Suddenly Die?

Black Spot

• Black spot is a very common fungal infection that attacks roses, especially in the late spring and early summer when the humidity is high and the temperatures are warm. Once the temperatures climb over 85 degrees Fahrenheit, the fungus stops growing. The actual organism is called Diplocarpon rosae, and it needs seven hours in a moist environment to reproduce. Water only the ground around the plant, and rake up any dead material around the plant where the spores might reproduce. Spray with a fungicide to reduce later infections.

Drought

• Roses need warm weather and lots of water to grow, especially when they grow into larger bushes. Supply your plants with 1 to 2 inches of water every week, and even more if the weather is especially hot. The lack of water causes rosebuds and blooms to wilt and droop. Severe drought yellows the leaves and kills the plant. Check to make sure your water is reaching deeper than 8 inches below the surface, and that the water is draining and not puddling in the soil.

Brown Canker

• Brown canker, Cryptosporella umbrina, is the most destructive of the top canker diseases of roses. The plants most bothered by this organism are floribundas, hybrid teas and hybrid perpetuals, while the rugosa, moss and brier roses show resistance. Brown cankers start as grayish spots bordered by a purple edge. As the cankers enlarge, they girdle the stems and kill the plant. Keep all debris away from the base of the plant, trim away any dead growth within the rosebush and sterilize your clippers between bushes.

Rose Stem Girdler

• Rose stem girdler, Agrilus aurichalceus, is one bug that attacks rosebushes, especially the Rugosa. The larvae burrows under the bark of the rose stem, causing a swelling in the area. As the bug travels within the rose cane, the swelling increases as the plant tries to heal the wounded area, and eventually the bug girdles the cane, killing the plant. Pesticides will control the bugs if you apply them in May and June while the adults try to lay their eggs on the rose plants.