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Publication #PP201

A Series on Diseases in the Florida Vegetable Garden: PEPPER 1

Gary Vallad, Ken Pernezny, and Tim Momol2

Many Floridians delight in maintaining a vegetable garden in their backyard. Others keep several pots of popular vegetables on patios or similar residential sites. Florida's long growing season and generally mild climate are ideal for the gardening enthusiast. What's more, the health benefits of moderate gardening activity are well documented, and the supply of wholesome garden-fresh vegetables adds to the quality of life in the Sunshine State.

Sometimes, however, pest problems interfere with gardening pursuits. Some problems, such as weeds and certain insects, are relatively easy to identify as causing damage. However, another group of maladies, plant diseases, can cause serious damage and are underappreciated and poorly understood by many homeowners.

The majority of plant health problems categorized as plant diseases are caused by microorganisms. As the name implies, these are extremely tiny disease agents that ordinarily require a microscope to be seen. The very minute size of these disease-causing pathogens accounts for the mystery that often surrounds the presence and impact of these pathogens in the garden.

Figure 1. 

A bacterial cell


Credit: Photo courtesy of J. B. Jones
[Click thumbnail to enlarge.]

The pathogenic microorganisms that attack garden vegetables, including pepper, can be classified into three major groups: bacteria, fungi, and viruses.

A 1000x magnification with a special light microscope is necessary to see bacteria (Fig. 1). They consist of only one cell and are usually spread by splashing water, as in rainstorms or overhead sprinkler irrigation. Bacteria can also be spread by gardeners who touch diseased plants and healthy plants in succession without thoroughly washing their hands in-between.

At a 100-400x magnification, fungi can be seen as threads (hyphae) that absorb food and water from their host (Fig. 2). Many fungi reproduce by forming thousands and thousands of spores that are readily blown about by even light winds. These spores can alight on pepper plants and eventually cause disease. Some fungi have the capacity to survive very long periods of time (10 years or more) in soil in absence of a host. Once peppers are planted in infested soil, these “resting” fungal structures can become viable again and attack plant roots, causing disease.

Figure 2. 

Microscopic threads (hyphae) and spores of a typical plant-pathogenic fungus.


[Click thumbnail to enlarge.]

Viruses are most strange, indeed. (Fig. 3). They are not “organisms” in the sense of fungi and bacteria. Instead, viruses are large molecular structures, consisting of a nucleic acid (DNA or RNA) wrapped in a protective coating of protein. Once inside pepper cells, viruses take over the host cellular machinery and use it to produce more viruses. Most of the important pepper viruses are transmitted to garden plants by insects -- such as aphids, whiteflies, or thrips.

Figure 3. 

Typical rod shaped virus as seen through a powerful electron microscope.


Credit: Photo courtesy of Scott Adkins, USDA
[Click thumbnail to enlarge.]

The following diseases are those that, in our experience, are most likely to appear on home gardeners' peppers. This list of pepper diseases is not by any means exhaustive, but includes the pepper diseases that seem to occur most often in Florida home gardens.

If you have a problem with your pepper plants that you think may be due to a disease not covered in this publication, search the EDIS database (http://edis.ifas.ufl.edu/) or the IFAS University of Florida Department of Plant Pathology website for information on additional pepper diseases.

Because legal uses and effectiveness of plant disease control chemicals change with time, consult your local UF IFAS Cooperative Extension office for current disease management recommendations.

Bacterial spot

Bacterial spot is one of the most common diseases of pepper every year in Florida, occuring in both commercial fields and home gardens. Bacterial spot is caused by the bacterium Xanthomonas euvesicatoria.

Figure 4. 

Bacterial spot on pepper leaf under moist conditions.


[Click thumbnail to enlarge.]

All above-ground parts of the pepper plant can develop bacterial spot symptoms. On leaves, the first symptoms are the appearance of spots on the lower leaf surface that look watersoaked. The spots are not actually wet, but have the distinct impression of being filled with water. The spots become brown to black in a few days and greasy looking (Fig. 4). The majority of leaf spots are surrounded by a yellow halo. Individual lesions (spots) may run together to form extensive blighted areas. In drier, cooler conditions, lesions may appear more tan to light brown without marked watersoaking (Fig. 5). Infected leaves may fall off plants prematurely, even when only a few spots form.

Figure 5. 

Bacterial spot on pepper leaf under dry conditions.


[Click thumbnail to enlarge.]

Symptoms on pepper fruit are very distinctive. These fruit lesions begin as small, raised pimples that are a bit lighter in color than the normal, dark-green fruit color. The lesions enlarge over time and become scabby looking (Fig. 6).

Figure 6. 

Bacterial spot on pepper fruit.


[Click thumbnail to enlarge.]

Control of bacterial spot is difficult once introduced into the garden. Therefore, do all you can to prevent introduction of the pathogen when the garden is established. If you start your plants from seed, purchase the seed from an established, reputable seed company. This will increase the likelihood that your seed is free of spot bacteria. When purchasing transplants from a retail nursery, inspect the plants carefully for symptoms of bacterial spot. Avoid purchase of diseased plants. Try to avoid overhead, sprinkle irrigation as much as possible. Bacterial spot is a warm, rainy-weather disease; problems with this disease can be minimized simply by growing peppers in the cooler, drier months.

Use of resistant varieties of pepper is another important strategy for control of bacterial spot. There are several types of the bacterial spot pathogen in Florida. These distinct types are known as races. Although at least 10 bacterial spot races are known, three of these known races (race 1, 2, and 3) have often been dominant in Florida. Several pepper varieties with resistance to races 1 through 3 are available for sale. Ask your seed supplier or transplant vendor if they have varieties with resistance to these bacterial spot races. Of course, if races other than 1, 2, or 3 attack, these varieties will not withstand the bacterial spot disease.

Copper-containing fungicide (bactericide) sprays that can be purchased at garden centers may provide some control of bacterial spot.

Anthracnose

Anthracnose is a fungal disease caused by Colletotrichum spp. It is a disease of both sweet bell, banana, and hot pepper fruits. Lesions (spots) can develop on fruit of any age, but symptoms are much more common on ripening fruit (i.e., those changing color from green to red, yellow, or a number of other mature colors).

Fruit spots are more or less circular and can enlarge rapidly, reaching diameters of 2 inches or more (Fig. 7). There may be concentric rings in the middle of these large spots, which are a direct result of growth of the fungus. Sometimes these rings are orange or salmon-colored due to the accumulation of large numbers of fungal spores.

Figure 7. 

Anthracnose symptoms on green pepper fruit.


[Click thumbnail to enlarge.]

Anthracnose is favored by prolonged periods of rain and high relative humidity. Anthracnose can occur throughout the range of temperatures that are possible for growing peppers in Florida, but is considered a disease of “moderate” temperatures (daytime highs in the 70s and 80s).

This disease can be especially difficult to control if it gains entry to a garden. If anthracnose is a continuing problem on ripe (colored) fruit, the gardener may have to consider harvesting more fruit when mature, but still green. Several fungicides will aid in control of anthracnose, but even use of these chemicals does not help very much if the weather is favorable for the disease. If chemical control is needed, the spray program must be initiated at the first sign of disease on the youngest fruit.

Cercospora leaf spot (frogeye leaf spot)

Figure 8. 

Cercospora leaf spot (frogeye leaf spot)


Credit: T. Kucharek and K. Pernezny
[Click thumbnail to enlarge.]

Cercospora leaf spot, also known by the rather peculiar term, frogeye leaf spot, is encountered on a regular basis in gardens in northern Florida. This fungus survives the winter in northern Florida and is most troublesome in warm, wet weather. Frogeye leaf spot is uncommon south of Orlando.

Symptoms occur in leaves, stems, and the stalks of both leaves and fruit. However, no symptoms of this disease occur on the pepper fruit themselves. Leaf lesions are quite distinctive and allow for quick and relatively easy field diagnosis. Leaf spots are circular to somewhat oval with a light tan center and a distinctive, dark-red border (Fig. 8). Under moist conditions, the causal fungus, Cercospora capsici, may be observed growing in the tan area of the spots, especially if a 10x hand lens is available.

Promptly destroy infected plants in the garden when your season ends in order to minimize carry-over to the next planting season. Fungicide sprays may be necessary if Cercospora leaf spot is a recurring problem.

Common virus diseases

A number of viral plant diseases affect pepper in Florida. These diseases have been noted occasionally in home-garden peppers. Most of the viruses that infect pepper are transmitted to healthy plants by aphids, tiny insects with piercing, sucking mouthparts that feed on plant sap. When aphids feed on virus-infected plants, the aphids may pick up virus on their mouthparts and infect healthy plants during subsequent feedings.

Symptoms of most of these viruses are quite similar, and laboratory tests are needed to identify exactly which virus is involved. Usually, however, it is not necessary for the home gardener to know which virus is the culprit; it is sufficient to know that the peppers have a viral disease.

Figure 9. 

Aphid transmitted virus symptoms on leaves and fruit of pepper


[Click thumbnail to enlarge.]

Virus-infected plants have mosaic patterns consisting of bands of light green or yellow alternating with dark green. Sometimes the leaves are crinkled or otherwise distorted (Fig. 9). Very often, plant growth is stunted. Mottled patterns and distortion may also be evident on fruit, with an uneven ripening of the fruit flesh (Fig.9). It is not uncommon for virus symptoms to be subtle; sometimes it takes a diligent and observant gardener to know that something is wrong.

A notable exception to the transmission of pepper viruses by aphids is tobacco mosaic virus (often abbreviated TMV). This is one of the oldest known viruses affecting pepper. This virus is mechanically transmitted; it is moved from plant to plant on the hands and clothing of gardeners and on contaminated garden tools. This virus may be introduced into gardens on infected transplants. Some tobacco products can be sources of TMV.

Virus disease management entails use of a number of tactics. Destroy solanaceous weeds (weeds in the same family as pepper, tomato, potato, etc.), such as nightshade and ground cherry. Remove infected plants at the first sign of disease. In South Florida, plant earlier in the fall to avoid the aphid flights traditionally associated with the cooler winter months (but remember, such early plantings are more likely to have problems with bacterial spot). Unfortunately, insecticidal sprays to control aphids have had poor success in controlling viral diseases.

With respect to TMV, avoid tobacco products when working around the garden. Use disease-free transplants. Washing hands and tools in milk, believe it or not, will do an excellent job of inactivating TMV and sharply reduce transmission of this disease.

Tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is such a unique virus that we chose to present it separately from the viruses in the previous section. This virus is spread primarily by the insect thrips and not by aphids. The symptoms of TSWV are often quite striking and consist of stunted plants (Fig. 10), mosaic and ring patterns (Fig. 11) on leaves and fruit and general browning of all above-ground plant parts.

Figure 10. 

TSWV on tobasco pepper


Credit: Photo courtesy of Hank Dankers
[Click thumbnail to enlarge.]

Figure 11. 

Ring pattern on leaf due to TSW


Credit: Photo courtesy of Hank Dankers
[Click thumbnail to enlarge.]

In Florida, this disease is found mostly north of Orlando, presumably because the thrips species that are best adapted to spread TSWV are more abundant in northern parts of the state. However, the disease may occur in South Florida, too.

Maintain good weed control to help reduce TSWV. Control of thrips with insecticides might help, but in controlled experiments, insecticides have not been all that successful. In order to keep the existing beneficial predator (i.e. Minute pirate bugs - Orius sp.) population, use thrips-specific insecticides when needed.

Footnotes

1.

This document is PP201, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date July 2004. Revised September 2008. Reviewed February 2012. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Gary Vallad, assistant professor, Plant Pathology Department, Gulf Coast Research and Education Center--Wimauma, Fla.; Ken Pernezny, professor, Plant Pathology Department, and associate director, Everglades Research and Education Center--Belle Glade, Fla.; and Tim Momol, professor, Plant Pathology Department, and district director, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Fl 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.