Capsicum annuum
| Damping-Off (fungi - Rhizoctonia solani, Pythium sp.): Small, emerging seedlings wilt and die soon after emergence. Root systems of surviving plants are damaged, resulting in stunted plants and poor yield. Use fungicide-treated, high-quality seed and plant on a well-drained bed. |
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Bacterial Leaf Spot (bacterium - Xanthomonas campestris pv. vesicatoria): Small, yellowish-green spots develop on the leaves [Picture 1]. The spots become brown and under favorable weather conditions, they become numerous, enlarge, and coalesce [ Picture 2]. This leads to defoliation [Picture 3]. The pathogen can also cause wart-like, dark brown spots on the fruit [Picture 4] or on the peduncle [Picture 5]. Damage caused by leafminer may be mistaken for bacterial leaf spot [Picture 6]. The pathogen is seedborne, but can also persist in crop residue. Splashing rain or overhead irrigation can spread the pathogen within the field. The disease is controlled by using clean seed and crop rotation. A copper spray program initiated on a preventative basis early in the growing season will reduce disease development. |
| Powdery Mildew (fungus - Leveillula taurica): Yellow areas that may become brown occur on the upper leaf surface [Picture 7]. A white, powdery growth occurs on the underside of the leaf [Picture 8]. Heavy infection may result in defoliation. The disease is favored by warm, humid conditions. It is not a common or significant disease in Texas. |
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Leaf Spot (fungus - Cercospora capsici): This disease rarely occurs in Texas. Spots on leaves are circular with light gray centers [Picture 9]. Spots may also be present on the stem. Severe leaf infection lead to yellowing and defoliation. The fungus is seedborne and can survive on crop residue. |
| Phytophthora Blight (fungus - Phytophthora capsici): The lower stem adjacent to the soil becomes brown [Picture 10]. However, a direct application of nitrogen fertilizer to the stems of transplants may cause similar symptoms [Picture 11]. The rotting of the stem results in wilting [Picture 12]. However, flooding of the roots for long periods of time can also cause wilting [Picture 13]. The fungus is soilborne, but splashing water can spread the fungus to above-ground portions of the plant, including fruit. Planting on a raised bed and avoiding excessive moisture through proper irrigation management will reduce the disease. |
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| Virus Diseases: Many viruses infect peppers. Sometimes, plants are infected by a combination of viruses. This, and the variation in symptoms produced as a result of cultivar and environmental differences, make identification of virus diseases by symptoms alone unreliable. A typical virus symptom is leaf mosaic, which is a mottled, non-uniform appearance of color. The pepper mottle virus, which is spread by aphids, causes such mottling [Picture 14]. Another virus, the Texas pepper geminivirus, which is spread by whiteflies, causes a yellowed, mottled appearance [Picture 15], in addition to leaf curling and distortion. Viruses can cause stunting; for example, the pepper mottle virus [Picture 16]. Some of the symptoms caused by the cucumber mosaic virus, which is transmitted by aphids, include vascular and fruit discoloration [Picture 17] or death of terminal portions [Picture 18]. The tobacco etch virus, which is transmitted by aphids, can cause mosaic, fruit distortion and stunting, but in the cultivar 'Tabasco', it can cause a lethal wilt [Picture 19]. Pepper-infecting viruses can infect other species of plants, often without producing symptoms. These viruses can be transmitted from such plants to peppers by feeding activities of insects such as aphids, whiteflies and leafhoppers. However, vector control is not usually a good strategy for virus control. By the time the vector is noticed on the pepper, the plants are already infected. Once a plant is infected with a virus, the infection can not be cured. If the infection occurs early in the life of the plant, there may be severe yield loss. In areas where pepper viruses and their vectors are endemic, the use of transplants or row covers can protect the plant during the early, critical growing period. Sometimes, cultivars resistant to a particular virus are available. Weed control both within and around a field may help by reducing the available virus reservoirs. Virus disease diagnosis can be difficult and can require the use of a plant disease diagnostic laboratory. To complicate diagnosis, sometimes agents other than viruses can cause virus-like symptoms. For example, a chimera can cause mosaic-type symptoms on leaves [Picture 20]. A chimera is a genetic mutation, which occurs rarely, i.e. one plant in a field. Persistent high temperatures (exceeding 100 F) at planting time can injure young seedlings, resulting in distorted foliage [Picture 21]. Broad mite injury can cause slight [Picture 22] or severe leaf distortion [Picture 23]. |
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Sunscald (physiological): Portions of the fruit have a dried, bleached appearance and are sunken [Picture 24]. The tissue is often colonized by saprophytic fungi, which give it a black, velvety appearance [Picture 25] and lead to the wrong conclusion that a fungus is the cause of the problem. This disease occurs as a result of exposure of fruit to direct sunlight and can be a consequence of the defoliation caused by leaf-infecting pathogens. |
| Herbicide Injury: Trifluralin (Treflan) injury can cause swelling of the stem near the soil line [Picture 26]. |
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Black Spot (unknown, possibly physiological): There are black circular or irregular-shaped spots on mature fruit that are beneath the epidermis and are not raised [Picture 27]. The discoloration extends to the interior of the fruit [Picture 28]. No pathogens have been found in association with this disease and factors required for its development are not known. The disease occurs occassionally in Texas. |