Impatiens Necrotic Spot Virus (INSV), formerly designated as Tomato Spotted Wilt Virus strain impatiens, is a serious disease of greenhouse flower crops such as impatiens, gloxinia, cyclamen, cineraria, begonia, and exacum. In addition to many flower crops, certain vegetables and weeds are also susceptible to INSV.
Symptoms - INSV can cause a wide range of symptoms on different host plants. Symptoms may include stunting, brown or yellow circular spots on leaves, ring spots, black or brown stem discoloration, browning of leaf veins, yellow line patterns in leaf tissue, or mosaic patterns (variegated patterns of light and dark green).
New Guinea impatiens samples were recently submitted to the Plant Disease Clinic that tested positive for INSV. Leaves were stunted and distorted. Distinct, necrotic (brown) ring spots were evident on some of the leaves. Other leaves showed a blackish/purple discoloration, often along leaf veins.
Spread - INSV is spread from plant to plant by western flower thrips. The virus may also be spread throughout the greenhouse industry by the movement of infected plants or cuttings.
Control - Infected plants cannot be cured of the virus and must be discarded. Monitoring and controlling thrips is critical in eliminating spread of the disease. Petunia plants can be used as indicators to monitor for the presence of the virus in a greenhouse. Cultivars such as Calypso, Super Blue Magic, and Summer Madness show brown ring spots around thrips feeding scars if the virus has been transmitted. Also, avoiding carrying plant material over from season to season will reduce the occurrence of virus disease problems.
This article originally appeared in the April 5, 1996 issue, p. 49.