Certain plant diseases which are soil borne can be controlled with some success through a
process of solar heating. This method can be used when space is limited and crop rotation is not
practical. It is much safer than using soil fumigants which are quite toxic and need to be used
with extreme care.
Solarization is a process by which the soil temperature is raised high enough to kill
insects, disease organisms and weed seeds which are in the soil. Its effectiveness is dependent
upon the soil reaching and maintaining a high enough temperature for a sustained period of time.
The easiest way to accomplish this is to cover moist soil which has been worked up or rototilled
with a clear sheet of thin polyethylene plastic film. Bury the edges of the plastic for a tight seal.
Leave the plastic in place for four to six weeks during the hottest part of the summer. Using a
thin clear plastic is preferred as black plastic reduces heat build up and thicker, clear plastic is
more reflective and also reduces heat build-up. Since the heating relies upon sunlight, this
method will be less successful in shady areas or during periods of cloudy weather.
Solarization is most effective in controlling nematodes, wilts, crown and root rots in
vegetable or flower garden areas. It may not be practical to use where a tree or shrub has died
from a soil borne organism and you want to replant with the same species. In these situations,
the best recommendation is generally to replant with a different species; one which is not
susceptible to the pathogen which killed the original plant.