References
Common diseases and disorders of Sansevieria and Yucca

A.R. Chase is a Plant Pathologist and President of Chase Research Gardens, Inc.
C.R.G. is a private research and consulting corporation specializing in ornamental plants.
Both hourly and contract services are available.
You can reach C.R.G. at P.O. Box 168, Mt. Aukum, CA 95656 Phone and Fax: 916-620-1624 - E-mail: MTAUKUM@AOL.COM

 
Aspergillus rhizome rot of Sansevieria
Pathogen - Aspergillus niger
Symptoms - Water-soaked spots on rhizomes become sunken as they mature. The outer layer may remain intact with inner tissue disintegrating rapidly. Spots near leaf bases or stem ends form and frequently contain the sooty dark brown to black spores of the fungus. The pathogen enters cuttings through wounds created during cutting collection. The disease is most severe during shipping.
Control - Disease control by keeping soil temperatures below 100F (using mulches of bark, sawdust or woodchips) is partially successful. Examine cuttings carefully for signs of infection and reject those that are not completely healthy. Use new or sterilized pots and potting media and grow plants away from the native soil.
Bacterial soft rot on Sansevieria
Pathogen - Erwinia carotovora
Symptoms - A mushy soft rot of the lower end of a cutting. Sometimes the plants have a fishy, rotten odor, characteristic of Erwinia infections
Control - Bacterial rot can be controlled through elimination of water on leaves. Choice of clean cuttings and strict sanitation are the most important control measures. Use of bactericides is not recommended due to very poor efficacy. Many other plants can be infected by Erwinia spp., and all should be inspected regularly for soft rot symptoms.
Cercospora leaf spot of Yucca
pathogen - Cercospora sp.
Symptoms - Initially, rust-colored specks form. Spots expand to 1/4-inch elliptical areas that are tan to brown.
Control - Protect plants from overhead irrigation and rainfall, if possible, to diminish spread of spores and the conditions needed for them to germinate and infect leaves. Remove leaves with symptoms and do not use cuttings with spots. No fungicides have been evaluated for control of this disease on yuccas, although thiophanate methyl has been used to successfully treat other Fusarium diseases. Always check fungicide labels for legal uses on each plant and follow rates and intervals as noted on the label.
Chilling damage of Sansevieria
Pathogen - Temperatures below 45F
Symptoms - Leaves are constricted in width in a narrow band across the leaf blade. Usually, constricted leaves have normal coloration. Cold-injured leaves develop whitish, water-soaked areas 1 to 4 weeks after exposure to cold
Control - Maintain temperatures at 45F or above. Prevent plant exposure to cold air or cold water (condensate or drips from the roof of the structure). Low air temperatures account for most of the injury in open stock beds, while cold water draining through perforations in polyethylene film used for lining shade houses accounts for most of the injury to Sansevieria in Central Florida. Use solid cover structures which are properly heated. Plants which are over-fertilized (especially with nitrogen) are more sensitive to chilling than those fertilized appropriately.
Coniothyrium or brown leaf spot of Yucca
Pathogen - Coniothyrium concentricum
Symptoms - Coniothyrium leaf spot first appears as tiny clear zones in older leaves of Yucca. Spots turn yellowish and finally brown as they mature. They are generally elliptical and are scattered across the entire upper surface of older leaves. After about 4 months, black fruiting bodies form in sunken centers and are easily seen with the naked eye. Sometimes a yellow border forms around the spots. This disease has been reported on many species of Yucca including Y. aloifolia, Y. filamentosa (Adam's needle), and Y. smalliana
Control - One of the most important aspects of control is the removal of older infected leaves and elimination of overhead watering or exposure to rainfall. Since most yuccas are grown exposed to both overhead watering and rainfall, regular applications of fungicides are needed to prevent disease. Weekly applications of chlorothalonil (Daconil 2787), zineb (Zineb), or mancozeb provided excellent disease control experimentally. Check labels of specific fungicides for yucca as well as rates and intervals of use.
Cytosporina or gray leaf spot of Yucca
Pathogen - Cytosporina sp.
Symptoms - Cytosporina or gray leaf spot of Yucca aloifolia (Spanish bayonet) has not been adequately described. Symptoms include tip and marginal necrosis with a predominantly gray color and brown margin. They often reach 3 inches wide, have concentric rings of light and dark tissues and are most common on older leaves. The black fruiting bodies of Cytosporina sp. can be found in these spots. This disease is not as common today as it was 20 years ago.
Control - Use the methods described for Coniothyrium leaf spot to control Cytosporina leaf spot of yuccas.
Fusarium leaf spot on Sansevieria
Pathogen - Fusarium moniliforme
Symptoms - Spots start as tiny water-soaked areas on immature leaves which rapidly enlarge into elliptical-to-irregular-shaped areas with a red or tan coloration. They are often surrounded by a bright yellow margin which can be 1/8-inch wide. As spots merge, immature leaves become distorted. Under optimal conditions, meristems of infected shoots die.
Control - Standing water in the central whorl of the plant is necessary for infection to occur. The high levels of water available during the rooting process are optimal for disease initiation and progress in cuttings. Complete disease control can be achieved if plant foliage is kept dry. Dracaenas are also susceptible to this pathogen. Chlorothalonil (Daconil 2787) has been especially effective in controlling Fusarium leaf spot experimentally. Check labels for legal plants, intervals, and rates.
Fusarium stem rot on Yucca
Pathogen - Fusarium spp., Nectria spp.
Symptoms - One of the most common diseases of rooted yucca cuttings is caused by Fusarium spp. Soft rot of stem ends develops with destruction of leaves as well. There are two types of fruiting bodies for the pathogen which are commonly produced on the infected tissue. These are the bright red perithecia, which are round and relatively easy to see with the naked eye, and the powdery clusters of conidia, which are ochre-colored
Control - Use only pathogen-free cuttings, use new or sterilized pots and potting media, and grow on raised benches. No fungicides have been evaluated for control of Fusarium stem rot on Yucca.
Southern blight on Yucca
Pathogen - Sclerotium rolfsii
Symptoms - This pathogen attacks all portions of the plant but is most commonly found on stems. White, relatively coarse mycelia grow in a fan-like pattern and may be seen on the soil surface or stems. The round sclerotia form almost anywhere on the plant or soil surface. Sclerotia are initially white and cottony and approximately the size of a mustard seed. As sclerotia mature, they turn tan, then eventually, they turn dark brown and harden
Control - Although this disease can be avoided through cultural methods, it continues to cause losses in production of foliage plants. PCNB (Terraclor 75) provides the most efficacious control of southern blight on many foliage plants. Application of this fungicide to some foliage plants results in stunting, and its use is restricted to once every 12 months. Check labels for legal plants, intervals, and rates.

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