RHIZOCTONIA DAMPING - OFF AND WEB BLIGHT OF PLUGS

One of the most common diseases associated with bedding plant plug production is Damping - Off caused by the fungus Rhizoctonia solani. The disease is characterized initially by the sudden collapse and death of the seedling within a few days after emerging from the medium. If the dead or dying seedlings are observed closely you may notice that the seedling is rotted off right at the medium line or crown of the plant. In some cases the roots may look relatively healthy. A factor that distinguishes this disease from damping - off caused by Pythium sp. In more advanced cases or when disease conditions are ideal, the brown web-like growth of the fungus can cover the entire surface of the plant. If left unchecked this web - like growth will advance rapidly from seedling to seedling causing a leaf and stem blight. In severe cases whole sections of seedlings in a plug flat can be wiped out within a few hours (Figure 1.) (Figure 2.) (Figure 3.) (Figure 4.) (Figure 5.)

The best way to control or manage Rhizoctonia damping - off and web blight is to not allow the environment in which the seedlings are growing to become favorable for the disease to develop. Rhizoctonia damping-off is a real problem when seeds are planted in, or seedlings are grown in a media that is not well drained. Over fertilization under dry conditions resulting in" burned" roots can also encourage the development of Rhizoctonia damping-off. Keep the root and seedling crown environment free from stress by planting seeds in media especially formulated for seedling production. Do not allow native soils into your seedling media. Most native soils are full of Rhizoctonia sp. and unless the soil is sterilized properly with steam, the fungus will gain entry into the production process. If the web blight phase of the disease is observed, removed the affected flats immediately and back off on overhead watering. Use chemical drenches to terminate the spread of the web blight.