Dark Spots on Rose Leaves and Leaves Turning Yellow

Characteristics

• Black spot is characterized by clearly recognizable round, black spots on leaves and stems, often with a yellow halo. Leaves turn yellow, then die and fall off. Stems blacken, shrivel and wilt. Sometimes, if the disease isn't noticed or treated in time, the entire plant will defoliate.

Conditions

• The black spot fungus requires water to spread the leaves and stems. The spores need to be wet for at least seven hours to germinate. The disease occurs when temperatures are between 65 and 80 degrees Fahrenheit, developing most rapidly at about 75 degrees. The fungus survives the winter on fallen leaves and infected canes to infect new growth in the spring.

Prevention

• Choose disease-resistant varieties of roses. Plant them in full sun with plenty of air circulation around them. Don't crowd them with other plants or plant them against a fence. Plant them in soil amended with rich compost and water them only at the base. Mulch the planting area with bark chips or compost to keep moisture levels even and discourage weeds. Clean up any fallen leaves. Begin spraying roses with fungicide as their first leaves emerge in the spring.

Treatment

• Pick off diseased leaves and put them in the trash; don't compost them. Fungal spores can infect fresh foliage if diseased leaves aren't removed. Cut off diseased stems, wiping your pruning shears with bleach after each cut. Spray the rose with an organic fungicide that contains sulfur or copper, or use a synthetic fungicide. Continue spraying, according to package directions, to keep the disease from spreading.