![]() Death by root rot is generally slower and more subtle. Plants affected by stem rot turn yellow, wilt, and collapse. Root rots also occur but are less commonly encountered. Jones, North Carolina State University, Rhizoctonia species sometimes cause stem rots of vinca plants and seedlings. Rhizoctonia stem and root rot on perennial groundcover vinca. See Table 1 for examples of brands and products. Mix and use according to label directions. Spray plants weekly with chlorothalonil as needed. Fungicides may be necessary for managing serious leaf spot infections. To reduce the overwintering population of the pathogen, remove dead plants from the garden after they are killed by a hard frost. Remove heavily infected plants immediately to minimize disease spread. Strive to maintain optimum soil pH and nutrient levels as low fertility increases disease severity. Therefore, avoid overhead irrigation whenever possible or water during pre-dawn hours, so the plants have plenty of time to dry before evening. Prevention & Treatment: Cultural practices that reduce the amount of moisture on the foliage and/or the length of time leaves remain wet will suppress this disease. As the spots increase in number, leaves turn yellow and drop from the plants. As they enlarge, light and dark bands may alternate within the lesion, giving it a target spot appearance. Spots caused by both fungi are small, ranging from the size of a pinhead to 1/8 inch in diameter. Symptoms first appear on lower leaves and stems, and if left unchecked, move upward. The fungi Alternaria alternata and Ulocladium species occasionally cause spots on foliage, stems, and petioles. Prevention & Treatment: See root rot management information under Phytophthora Stem Blight and Root Rot. This pathogen does not cause branch blight, only root rot and damping off of seedlings. The pathogen that causes this disease is closely related to Phytophthora species, so root rot symptoms are similar. Read the label completely and apply all chemicals according to the directions on the label. ![]() For aerial blight, use sprays of potassium salts of phosphorous acid, copper sulfate, copper ammonium complex, copper soap, or chlorothalonil. For root rot, use potassium salts of phosphorous acid as a soil drench. The remaining plants can be treated with a fungicide if cultural practices fail to prevent new infections from occurring. ![]() Adding organic materials, such as composted pine bark, to the soil will help increase drainage due to improved soil structure. When preparing a plant bed, thoroughly dig up the whole area. To help prevent root rot, it is also important to provide excellent drainage. Avoid excessive amounts of fertilizer as well. When rainfall is insufficient to supply an inch of water per week, apply deep supplemental irrigation once, or possibly twice per week, depending on soil type, sun exposure, and weather conditions. Annual vinca and Vinca species are fairly drought tolerant, so water only as needed. Frequent watering, even in moderate to dry sites, can make conditions favorable for the development of branch blight and root rot. Prevention & Treatment: Water management is the main preventative measure. Plants with root rot have reduced root systems, and individual roots tend to slough off the outer tissue, leaving the inner core behind. Symptoms of root rot include yellowing and scorching of leaves, poor growth, and stunting of plants, followed by wilting and death. Dark brown to black lesions form on stems and branches, causing the portions above to wilt and die back. Stem and branch blight frequently occurs without root rot, but root rot is involved in some cases. Annual vinca with Phytophthora stem blight and root rot.ĭepartment of Plant Pathology Archive, North Carolina State University, Aerial stem blight and root rot are caused by Phytophthora nicotianae and occasionally other species.
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