Pest Spotlight: Root Rot and Phytophthora Stem Blight

Annual vinca with Phytophthora stem blight and root rot
Department of Plant Pathology Archive,
North Carolina State University, www.forestryimages.org

Root rot is a common fungal infection to plants created by overwatering, excessive rains and other moisture and pH environmental factors. Learn more about the disease with information from the Clemson University Extension, publication HGIC 2108 pertaining to vinca infections of root rots.

Phytophthora Stem Blight & Root Rot: Aerial stem blight and root rot are caused by Phytophthora nicotianae and occasionally other species. Stem and branch blight frequently occurs without root rot, but root rot is involved in some cases. Dark brown to black lesions form on stems and branches, causing the portions above to wilt and die back. Symptoms of root rot include yellowing and scorching of leaves, poor growth and stunting of plants, wilting and death. Plants with root rot have reduced root systems and individual roots tend to slough off the outer tissue, leaving the inner core behind.

Prevention & Treatment: Water management is the main preventative measure. Frequent watering, even in moderate to dry sites, can make conditions favorable for development of branch blight and root rot. Annual vinca and Vinca species are fairly drought tolerant, so water only as needed. 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, exposure and weather conditions. Avoid excessive amounts of fertilizer as well. To help prevent root rot, it is also important to provide excellent drainage. When preparing a plant bed, thoroughly dig up the whole area. Adding organic materials, such as composted pine bark, to the soil will help increase drainage due to improved soil structure.

Remove and destroy infected plants. The remaining plants can be treated with a fungicide if cultural practices fail to prevent new infections from occurring. For root rot, use fosetyl-Al (Monterey Aliette) or phosphorous acid (Monterey Agri-Fos Systemic Fungicide) as a soil drench. For aerial blight, use the products above, copper sulfate products (such as Bonide Copper Fungicide or Dexal Bordeaux Powder), copper ammonium complex products (such as Monterey Liqui-Cop Fungicide Concentrate or Southern Ag Liquid Copper Fungicide), copper soap (Bonide Liquid Copper Fungicide, Camelot Fungicide/Bactericide Concentrate, or Natural Guard Copper Soap Liquid Fungicide Concentrate), or chlorothalonil products (such as Ferti-lome Broad Spectrum Landscape & Garden Fungicide, Garden Tech Daconil Fungicide, Ortho Garden Disease Control, Ferti-lome Broad Spectrum Landscape & Garden Fungicide, Bonide Fung-onil Concentrate, or Tiger Brand Daconil). Read the label completely and apply all chemicals according to directions on the label.

Pythium Root Rot: The pathogen that causes this disease is closely related to Phytophthora species so root rot symptoms are similar. This pathogen doesn’t cause branch blight, only root rot and damping off of seedlings.

Prevention & Treatment: See root rot management information under Phytophthora Stem Blight and Root Rot.

Rhizoctonia Stem & Root Rot: Rhizoctonia species sometimes cause stem rots of vinca plants and seedlings. Root rots also occur, but are less commonly encountered. Plants affected by stem rot turn yellow, wilt and collapse. Death by root rot is generally slower and more subtle. Affected plants are stunted, their roots have brown lesions, leaves turn yellow and plants wilt even when soil moisture is sufficient.


Rhizoctonia stem and root rot on perennial groundcover vinca.
R.K. Jones, North Carolina State University, www.forestryimages.org

Prevention & Treatment: Purchase only healthy, green plants. Inspect the roots if there are any doubts. Make sure plants aren’t installed too deeply. Apply supplemental water only as needed and water thoroughly when an application is made. Light, frequent waterings encourage the growth of stem rot pathogens because of increased humidity levels near the stem. Frequent watering can also exclude oxygen from the root zone, which encourages root rot pathogens. Remove and destroy plants that are clearly diseased, making an effort to remove all roots when root disease is present. Fungicides can be applied to the remaining plants if necessary. Products containing thiophanate methyl (such as, Cleary’s 3336-WP Turf & Ornamental Fungicide or Southern Ag Thiomyl Systemic Fungicide), chlorothalonil (such as Ferti-lome Broad Spectrum Landscape & Garden Fungicide, Garden Tech Daconil Fungicide, Ortho Garden Disease Control, Tiger Brand Daconil, or Bonide Fung-onil Concentrate), and iprodione (Rovral or Rovral 4F) can be used. Apply according to label directions.

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