By Mike Matheron, UA Extension Plant Pathologist

With summer officially here, constant triple-digit daytime temperatures will be the norm until at least the beginning of autumn.

Summer is the perfect time for soil solarization. The solarization of soil is accomplished by covering moist soil with clear plastic, allowing the sun’s energy to heat the soil over a period of time.

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 a few years ago in Yuma, the average temperature of soil was 113 degrees F. at a depth of two inches during a one-month summer solarization period, compared to 102 degrees for non-solarized soil. The average peak afternoon temperature in solarized soil during the trials was 128 degrees.

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

Soil solarization, like any other cultural practice, has its benefits as well as drawbacks.

Documented benefits include significant population reductions of different soil-borne plant pathogens plus viable weed seeds. The drawbacks include the cost of buying, laying, maintaining, and removing the plastic film.

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Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.