Soil solarization

By Mike Matheron, UA Extension Plant Pathologist

Summer is upon us and so are the triple digit temperatures that we in the desert will endure until at least the beginning of autumn in mid-September. Although we may not personally appreciate the daily exposure to the summer heat, it is the perfect time for soil solarization.

Solarization of soil is accomplished by covering moist soil with clear plastic and allowing the sun’s energy to heat the soil.

A great deal of research in diverse geographical regions has demonstrated that soil solarization can raise temperatures to levels lethal to many different types of plant pathogenic fungi. The plastic serves to conserve soil moisture and retard heat loss.

In field solarization trials conducted from 2004 to 2007 in Yuma, the average temperature of soil at a depth of two inches during a one-month summer solarization period was 113 degrees F., compared to 102 degrees F. for non-solarized soil. The average peak afternoon temperature in solarized soil during these trials was 128 degrees F.

In these solarization trials conducted in soil naturally infested with the lettuce Fusarium wilt pathogen, the incidence of this disease in a subsequent planting of lettuce was reduced from 42 percent to 91 percent compared to disease levels in non-solarized plots.

Soil solarization, like other cultural practices, has benefits and drawbacks. The advantage of plant pathogen reduction was mentioned earlier. One disadvantage is the cost and handling of the plastic film.

Contact Matheron: (928) 726-6856 or