Lettuce Base Rot

photo: gerald holmes
Latest Update 16th December 2014.

Lettuce Base Rot.
  • Binomial name:                        Rhizoctonia solani.
  • Family:                                    Ceratobasidiaceae.
Notes.
  • Lettuce base rot is a fungal plant pathogen present in most soils around the world.  Although it appears to work in partnership with other fungi, Rhizoctonia solani (Rs) is the active partner when attacking lettuce roots and stems.
  • Rs lives in the soil and its fungal hyphae invade the roots of a wide range of crops causing diseases which disfigure and ruin them.  Warm wet soil of low fertility and high compaction are its favourite growing environment. 
  • It is difficult to eradicate, but in rich, friable organic soil it is vulnerable to soil borne predators such as Bacillus pumilus, which prevents Rs's spores from germinating.   
Why Lettuce Base Rot is a Disease.
  • The fungal hyphae of Rs attack lettuce roots first.
  • They extend upwards into the body of the plant through the outer stems and leaves, and eventually invade the whole plant causing it to rot wherever they go.
Disease Control.
  • Crop rotation reduces the effectiveness of Rs by depriving it of its food for a few years.
  • Highly beneficial microbial activity in the soil can be maintained by frequent applications of high quality organic matter such as homemade compost and composted animal manures.
  • Regular foliar sprays of aerated compost tea help strengthen the lettuce plant and stimulates growth in its vulnerable root tips to quickly penetrate the soil zone occupied by the Rs fungi without infection.
  • Keep digging tools clean to prevent the spread of Rs fungal spores.
  • Regularly replace mulch and dispose of old mulch and any diseased plant tissue in a hot compost or buried deep in the soil (not in an Ecobed).