Impatiens Necrotic Spot on Pepper Transplants see below

This Week: Impatiens Necrotic Spot on Pepper Transplants

From: Nancy Taylor and R. M. Riedel, Plant Pathology, OSU and Bob Precheur, Horticulture and Crop Science

Some pepper transplants came into the Plant and Pest Diagnostic Clinic last week with Impatiens Necrotic Spot. A discussion of symptoms and management of this disease as well as other viral diseases of greenhouse floral crops is given in a fact sheet by Dr. Stephen Nameth, excerpts of which appear below.

The Complete Fact Sheet, Virus Diseases of Greenhouse Floral Crops, HYG-3065-96, Stephen Nameth

Excerpts From the Fact Sheet: There are a variety of viruses that can infect floral and vegetable crops, most of which are moved from plant to plant by insects. Most virus diseases can be identified by the type of symptom they induce in the plant; however, positive identification needs to be done in cooperation with a plant diagnostic clinic.

Symptoms
Symptoms associated with floral crop viruses vary substantially with the virus and the particular host that is affected. The same virus can cause different symptoms in different hosts. Symptoms such as mosaic, ringspot, necrotic spot, leaf blistering and deformation are all symptoms associated with floral plant viruses. Other symptoms of the more general type can also be associated with virus infection. These include yellowing, stunting, and wilting. This general group of symptoms sometimes complicates the diagnostic process, as they are also symptoms associated with other types of floral crop pathogens.

Causal Agents and Disease Development

Most virus diseases in the greenhouse are associated with five common viruses. These are Impatiens Necrotic Spot Virus (INSV), Cucumber Mosaic Virus (CMV), Tobacco Mosaic Virus (TMV), Tomato Ringspot Virus (Tom RSV), and Tobacco Ringspot Virus (TRSV). In impatiens, INSV first expresses itself as a black or necrotic spot associated with the leaves or stems of a small plant or seedlings. These spots can later become larger or develop into black or necrotic ringspots (See below: Figure 1).

Symptoms of Impatiens Necrotic Spot in Peppers
Hosts - Many, particularly hosts that attract thrips

	Figure 1. Closeup of Black, necrotic ringspots on pepper leaf
	Figure 2. Symptoms first begin as black, necrotic spots on pepper leaf Note ringspot starting to develop,
	Figure 3. Black lesions on affected stems, wilting.

In other hosts such as Gloxinia, Cineraria, or Dahlia, INSV induces concentric rings of almost perfect proportion. In New Guinea impatiens, symptoms may not be seen until the plants flower, even though plants were infected earlier. Disease Management

Vector Control

Since most viruses are spread or vectored by insects, one of the most effective ways of controlling viruses in the greenhouse is to control insect vectors. Thrips are the primary means by which INSV spreads about the greenhouse. Getting thrips populations under control can dramatically reduce the incidence of INSV in your crop. Other insects such as aphids and whiteflies can also spread viruses. For additional information please refer to Ohio State University Extension Bulletin 538, Insect, Mite and Disease Control on Commercial Floral and Foliage Crops.

Sanitation

Tobacco mosaic virus can easily be moved from one plant to another by just the touch of a hand or the carryover of sap on a cutting knife. For this reason it is extremely important to keep hands and propagation tools free of sap when going from plant to plant. Wash hands in warm soapy water and dip (disinfest) tools in a 10% chlorine bleach solution. Weeds can also play a role in the transmission of viruses. Weeds serve as alternate or secondary hosts for plant viruses as well as their insect vectors. Keeping weed populations in and around the greenhouse to a minimum is a good sanitary practice that will aid greatly in controlling viruses.

Chemical Control

There are no chemicals that will cure a plant of a virus infection. Chemicals are helpful in insect and weed control. That is why it is so important to practice all of the nonchemical disease management practices mentioned above. Table 1. Common Viruses of Floral Crops and the Symptoms They Induce Virus Floral Crop Hosts Affected Symptoms Associated with Infection

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