Double impatiens are brightly colored annual flowers that thrive in shade and provide a burst of color to the area. Native to Australia and South America, these showy flowers are more expansive, taller and brighter than common impatiens. They feature glossy foliage and blooms that resemble roses. There are a few diseases impatiens are susceptible to that adversely affect their growth and health.
Diseases common in double impatiens include necrotic spot virus, vascular wilt, rhizoctonia crown rot, powdery mildew and leaf spots.
Necrotic spot virus spreads by insects called western flower thrips, which are especially attracted to double impatiens and cause severe damage to the plants. Soil pathogens cause vascular wilt disease and affect double impatiens at any stage of development. Rhizoctonia crown rot (Rhizoctonia solani) is a fungal disease that affects the entire plant. Powdery mildew and leaf spots are diseases also caused by fungi.
Necrotic spot causes black rings or spots with tan/black centers and brown borders of infected stems of leaves. Leaves also wilt, distort in shape or turn yellow, and entire plants may collapse. Although vascular wilt infects plants at any stage, it is more likely to attack established beds. This disease causes young plants to suddenly dry up, or older ones to develop a light green color, with lower leaves wilting. Black streaking on the vascular tissues appears upon cutting the stem. Symptoms of Rhizoctonia crown rot include wilting or yellowing of the entire plant, or sudden collapse accompanied by black or brown lesions on the lower part of the stem near the soil. Powdery mildew appears as white powdery patches or spots on the upper surface of leaves and sometimes stems, and occurs during hot weather. Leaves heavily infected turn brown and sometimes shrivel. Symptoms of leaf spots include brown or black spots with purple margins that appear on the lower leaves first and slowly spread upward.
No cure exists for double impatiens infected with necrotic spot virus. Remove infected and damaged plants immediately and discard the soil as well if the flower was potted. Focus on preventive methods to avoid infection from this disease in the future. Curing impatiens with vascular wilt is difficult because the pathogens that cause it are present in the soil and chemical control methods for these fungii are ineffective. As there is no cure for Rhizoctonia crown rot, it is extremely important to prevent this disease; control can be achieved by spraying the plant with fungicide. Remove double Impatiens plants that exhibit symptoms immediately. To cure powdery mildew, apply fungicides that contain registered compounds. Pluck off infected leaves and dispose of in a knotted garbage bag immediately to prevent the spread of fungus spores. To cure leaf spots, apply fungicide containing sulfur or chlorothalonil to new growth in spring, and pluck and discard infected leaves.
Prevent necrotic spot virus by controlling thrip population. Apply insecticide over the area every three to five days. Repeated planting of impatiens in the same area increases chances of vascular wilt, so rotate plants every year. Also, handle plants carefully to prevent root injury through which the fungi enter easily. Prevent Rhizoctonia crown rot by watering the plant at soil level--being careful not to overwater--and provide adequate spacing between the double impatiens plants to allow air to circulate. Adequate spacing between plants also helps to prevent powdery mildew. Water and fertilize double impatiens appropriately to promote maximum health and vigor, and thereby minimize their susceptibility to leaf spot disease. Water early in the morning so foliage is dry by evening.