Sclerotium rolfsii

Southern Blight is a serious fungal disease affecting a wide variety of both food crops and ornamental plants. Southern blight is a serious problem for both agriculture and the nursery industry, and is very hard to eradicate once established in a garden.

Symptoms and Signs

Affected plants show signs including wilted leaves and soft, rotten crowns, often followed by the death of the infected plant.

The fungus is microscopic when inside the plant tissue, but eventually the organism forms sclerotia, which are an asexual dormant body which are visible to the naked eye, and look like white, yellow, or brown mustard seeds.

Life Cycle

The fungus overwinters as a sclerotium, which is a dense mass of hyphae with a hard outer shell. When Warm, humid conditions are present, the sclerotia "germinate", and infect plant parts. The pathogen is not systemic on the plant, so removing infected parts can help control the disease.

Host Range by Genus

Controls

• Exclusion: Once established, this pathogen is very difficult to get rid of, so care should be taken when introducing susceptible plants to the garden, and pinfected plants should be removed as soon as the infection is discovered.

Bulbs and corms can be treated with hot water for 30 minutes ^[1]

When working around infected plants, tools and shoes should be cleaned.

• Cultivation: The sclerotia only become active when on the surface of the soil, so a deep top-dressing with compost may help control the disease. Removal of the mulch layer in winter is also recommended, as this both physically removed the sclerotia and exposes the soil to winter dessication.

Adding composts raises the level of antagonistic organisms.

Deep plowing can also provide some control by burying the sclerotia.

Plastic mulches can serve as a barrier between the innoculant and plant tissues.

• Cultural Controls: Crop rotation is sometimes tried as a control, but this can be difficult to to the wide host range, however rotation with resistant Allium species

Avoid dense leaf canopies, in order to let the soil surface remain dry.

Keep litter and weeds out of the garden.

Solarization can kill the fungus in the top layer of soil, in regions where solarization can bring about high enough temperatures.

• Physical Removal: Removal of infected plant and soil is strongly recommended. Mulch around infected plants should be removed at the end of the season.
• Chemical Controls (synthetic): ^[2]Methyl Bromide and Methyl Bromide/Chloropicrin have been applied as soil fumigants, however both are extremely dangerous chemicals and are banned in many regions.

PCNB (Terraclor) at 0.5-1 lb a.i./1000 sq ft can be incorporated into the soil surface.

• Biocontrols: Trichoderma harzianum, T. viride, Bacillus subtilis, Penicillium spp., and Gliocladium virens.
• Disposal: Safe only in hot compost piles.

External links

• http://www.extento.hawaii.edu/Kbase/Crop/Type/s_rolfs.htm - host range
• http://www.extension.umn.edu/yardandgarden/ygbriefs/p152southernblight.html - cultural controls
• http://www.ipm.ucdavis.edu/PMG/r280100711.html - chemical fumigants
• http://www.ppdl.org/dd/id/southern_blight-hosta.html - resistant species

References