Soil Pasteurization, Fumigation, and Solarization
Soil Solarization
Solarization is a form of soil pasteurization whereby solar energy is trapped under clear polyethylene film spread on the soil surface of the greenhouse (Figure 13.2). In desert environments, soil temperatures in the top 6 inches of soil reach 140 degrees F (60°C). The effect of solarization is greatest at the surface and decreases with depth. However, under optimal conditions, heating is sufficient in the top 12 inches of soil to be effective against a wide range of pathogens and pests. It is a cheap and effective means in controlling many important soilborne fungal and bacterial plant pathogens, including those that cause Verticillium wilt, Fusarium wilt, Phytophthora root rot, Southern blight, damping off, crown gall disease, tomato canker, potato scab, and many others. A few heat-tolerant fungi and bacteria are more difficult to control with solarization. Soil solarization can be used to control many species of nematodes. Soil solarization controls many of the annual and perennial weeds.
Site Preparation
A smooth bed, with clods and litter raked away, is best because the plastic will lie snugly against the soil and have fewer air pockets. The area to be treated should be well tilled and free of clods and crop debris. Solarization can be done on flat areas or raised beds.
Film Selection and Application
Clear polyethylene film of various thicknesses (0.5–4ml) should be used. Thinner (0.5–1mil) films conduct more heat, but are more susceptible to tearing and have a shorter life than thicker films. Agricultural films for commercial application are often treated with ultraviolet (UV) inhibitors to delay film breakdown.
Intensity of Solarization
The degree various pests can be controlled is related to the intensity, depth, and duration of the elevated soil temperatures. Solarization is both time and temperature dependent. The cooler the soil temperatures, the longer the plastic needs to remain in place to raise the temperature to desired levels.
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