References
Common diseases and disorders of Cacti and Succulents

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

 

Anthracnose on Sedum
Pathogen - Colletotrichum gloeosporioides
Symptoms - Leaf and stem spots appear as soft areas with sunken centers. These spots can turn black or tan depending upon the plant. The spores of the fungus are orange colored and are easily transferred by splashing irrigation water or rainfall.
Control -This disease is rarely a problem on mature or well rooted plants as wounds appear to be critical for infection to occur. For this reason special care in protecting rooting cuttings can generally control the problem completely. Plants that are susceptible include: Crassula, Graptopetatum, Sedum, and Sempervivum.

Botrytis blight on Senecio
Pathogen - Botrytis cinerea
Symptoms - Botrytis blight usually appears on leaves of cuttings in contact with the potting medium or in the center of the plant where the humidity stays high. The water-soaked spots enlarge rapidly to encompass a large portions of the plant. When night temperatures are cool, day temperatures warm, and moisture conditions high, the pathogen readily sporulates on infected plant parts, covering them with grayish-green dusty masses of conidia (spores).
Control - Controlling Botrytis blight on most plants is particularly important during the winter months in the Southeastern US. Methods which improve drying and reduce moisture condensation on plants during the nights reduce the need for fungicide application. Iprodione (Chipco 26019 50WP) and vinclozolin (Ornalin 50WP) are effective in controlling Botrytis blight on many plants but labels must be checked for legal uses on each plant. This disease is rarely found in commercial production of succulents and cacti.

Dichotomophthora rot on Opuntia
Pathogen - Dichotomophthora indica
Symptoms - Spots are generally tan and may be dry at times and appear sunken. The black spores of the pathogen are sometimes found within the spots, and they spread easily by splashing water. There are only a few cacti reported as hosts of this pathogen (Opuntia and Gymnocalicium), however many more are probably susceptible.
Control - See controls listed for Helminthosporium blight.

Fusarium rot on Faucaria and christmas cactus
Pathogen - Fusarium oxysporum
Symptoms - Dieback, root and cladophyll rot may occur as a result of the Fusarium infection. Species of Schlumbergera, Rhipsalidopsis and indeed most cacti and succulents produced commercially are susceptible to F. oxysporum. An infection appears at the cladophyll border or in plant centers. Spots are generally tan and may be dry at times and appear sunken. The orange-colored spores of the pathogen form in the lesions, and they spread easily by water or air since the spores are light weight. Abscission of cladophylls above the affected portion can occur when conditions are wet and warm. In addition, when moisture is high the mycelium of the fungus can develop extensively and cover the entire plant. Nearly all cacti and succulents are susceptible to Fusarium diseases.
Control - Use the same cultural controls as listed for soft rot. Thiophanate methyl (Domain or Cleary 3336) is labeled for use on some cacti and is effective in controlling Fusarium diseases. Mancozeb (Dithane T and O) is labeled for christmas cactus and may also aid in disease control. Reduction of water applications greatly reduces spread of the pathogen to aerial portions of the plants, thus reducing disease severity.

Helminthosporium rot on Easter cactus and Cereus
Pathogen - Drechslera cactivora
Symptoms - Blackened, sunken lesions from 1/16 to 1/2 inch across form anywhere on the above ground portions of the plant. The spots on holiday cacti are generally circular and can occur below ground. Cladophyll abscission is common on plants even when infection appears light. The black spores of the fungus form in the spots, giving them a fuzzy appearance. The disease was first described in the mid 1950's on Cereus and remains a problem for some producers today. A rapid rot of the cotyledons of young cacti is one of the first symptoms. Older plants become rotted where spines have broken or the stem has been punctured. Most plants become blackened and may be mush or dryish with collapse of the affected portion. Rhipsalidopsis is very susceptible to Drechslera leaf spot and Schlumbergera is moderately susceptible. Helminthosporium infects a number of cacti and succulents in addition to Cereus and the holiday cacti.
Control - Use the same cultural controls as listed for soft rot. In addition, sprays and drenches of chlorothalonil (Daconil 2787 formulations) are very effective in controlling the disease but should be used with caution since it has been shown to cause slight chlorosis occasionally. Mancozeb (Dithane T and O) is labeled for some plants and may also aid in disease control.

Pythium root rot on Easter cactus
Pathogen - Pythium spp.
Symptoms - Foliage of plants infected with Pythium spp. turns a dull gray-green and may wilt. Stems become rotted at the soil line and upper portions of the plant collapse. Cladophyll abscission may occur. Roots are darkened and mushy and generally sparse.
Control - Use pathogen-free pots and potting media and grow plants on raised benches. Over watering plants may predispose them to attack by root-rotting fungi. Soil drenches with the combination of etridiazol and thiophanate methyl (Banrot), etridiazol (Truban and Terrazole formulations) or metalaxyl (Subdue 2E) each are labeled for some cacti and succulents and aid in control. Most cacti and succulents can be infected with Pythium spp. if they are over watered or planted in poorly draining potting medium.

Soft rot on Easter cactus and Hawarthia
Pathogen - Erwinia spp.
Symptoms - A blackened, wet, slimy spot generally starts at the soil line at the base of the plant and progresses into the top of the cladophyll or into the upper portions of the plant. Plants wilt, collapse and often die. Due to production of a special enzyme, infected plants become very mushy and disintegrate especially during the warmer months of the year.
Control - Remove and destroy infected plants as soon as they are found. Keep watering to a minimum and avoid splashing since this can spread the bacterium to other plants. Irrigate early in the day to allow rapid drying of the foliage which reduces the ability of the bacterium to infect. Be sure to obtain an accurate diagnosis of the problem since several of the diseases caused by fungi appear similar. Use of bactericides on plants infected with Erwinia spp. is rarely effective. Most cacti and succulents will die if infected with Erwinia spp. so prevention is the key to control.

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