Also known as crown rot and white mold, Southern blight is a disease caused by the fungus, Sclerotium rolfsii. As the name implies, this was once a problem primarily in the hot, humid south but has recently been moving into the upper midwest (global warming?).

There are over 200 different genera of plants that are susceptible to this disease. In the home landscape, common hosts would include daylily, astilbe, hostas, peony, phlox, ajuga, and delphinium.


Although its symptoms can be similar to other diseases, the first signs of Southern blight would include yellowing of foliage and wilting of leaves. This disease attacks at or just below the soil line so there may be black or dark brown lesions on the lowest part of the stem. In hosta, it may appear as a brown rot at the base of the leaf petioles.

One of the best characteristics for identification is the development of cottony white, threadlike wisps called mycelium that grow up the stem and may spread out on top of the soil.

The fungus overwinters as a very small, brown or tan colored structure called the sclerotia. These can be found on the surface of the soil near infected plants. It was thought that the reason the disease was found mostly in the South was that these structures could not survive the winter cold up North. However, it appears that they can live as long as they are covered by a layer of snow or organic mulch.

A related disease, white mold caused by a relative fungus, Sclerotinia sclerotiorum, is quite similar. It seems that the distinguishing feature is that the sclerotia of this disease are larger (about the size of small rabbit droppings) and they are usually attached to the lower stem of infected plants.


Perhaps the best way to deal with Southern blight is to be aware of which plants are susceptible and, if you have been having a problem with this disease in your landscape, avoid planting these to replace lost plants.


Since this is a soil borne fungus, once it is present in your landscape, it is very difficult to eliminate. To do so would require sterilization of the soil and that is a tough task. Some commercial pest control companies may have specialized equipment and access to potent chemicals that can sterilize large amounts of soil in the garden.

Some home gardeners have tried treating small areas around where herbaceous perennials have died with this disease. They have used a dilute solution of chlorine bleach (one part bleach to nine parts water) to treat the soil before replanting.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.


Some plants susceptible to Southern blight (Scleratium rolfsii):
*Southern blight has been reported on hundreds of plants. This is a partial list of plants that are frequently infected by this disease.
SHRUBS  
Daphne
Hydrangea
Rosa
 
 
FLOWERS  
Alcea - Hollyhock
Anemone
Calendula - Pot Marigold
Caillstephus - China Aster
Campanula - Bellflower
Canna
Chrysanthemum - Mum
Cosmos
Dahlia
Delphinium
Dianthus - Pinks, Sweet William
Gladiolus
Hosta
Iris
Lathyrus - Sweet pea
Lilium - Lily
Lupinus - Lupine
Narcissus - Daffodil
Phlox
Rudbeckia - Blackeyed Susan
Scabiosa - Pincushion Flower
Sedum - Stonecrop
Tagetes - Marigold
Tulipa - Tulip
Viola - Pansy, Viola, Violet
Zinnia

 

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