Soil solarization

Soil solarization works by trapping solar energy under a transparent polyethylene tarp, raising soil temperatures to levels that are lethal or sublethal to a wide range of organisms. The soil is first tilled, irrigated to field capacity, and then covered with a thin (25–50 µm) clear plastic film for 4–6 weeks during the hottest part of the year. Moisture is essential because wet soil conducts heat more efficiently and makes target organisms more susceptible to heat stress. The tarp must be kept tight and free of tears to maintain the greenhouse effect. Temperatures typically reach 40–60°C at 5–10 cm depth, and the cumulative heat exposure (degree-hours) is the key factor determining efficacy.

Solarization is effective against many soilborne pathogens, including Fusarium, Verticillium, Pythium, and Phytophthora species, as well as nematodes and weed seeds. It is particularly successful against heat-sensitive organisms in the upper soil layers; deeper or heat-tolerant organisms may survive. Efficacy varies with climate, soil type, and tarp quality. In California, solarization has been used to manage Verticillium wilt in strawberry fields, reducing pathogen populations significantly. In Israel, it has been integrated into integrated pest management for tomato and pepper production.¹ The method is less effective in cool or cloudy regions, and it does not eradicate all pests, so it is often combined with other practices.

The primary advantage of soil solarization is its environmental safety: it leaves no chemical residues, preserves beneficial soil microorganisms, and is compatible with organic farming. It also improves soil structure and nutrient availability. However, the technique requires a long fallow period, clear weather, and a reliable water supply. It is labor-intensive and may be impractical for large-scale operations. Additionally, solarization can inadvertently kill beneficial organisms, and it may not control all pests, such as certain root-knot nematodes or heat-resistant weed seeds. Cost-effectiveness depends on local conditions and the value of the crop.²

Beyond its conventional use, solarization has been adapted for specialty applications. In greenhouse production, it is used to disinfect potting media and raised beds. Researchers have explored combining solarization with organic amendments, such as chicken manure or mustard meal, to enhance pest control through biofumigation. Solarization also shows promise in restoring degraded soils by reducing weed pressure and promoting beneficial microbial communities. In some regions, it is used to manage Fusarium wilt in banana plantations, and it has been tested for controlling Phytophthora in avocado orchards. A lesser-known fact is that solarization can also reduce the viability of plant-parasitic nematode cysts, though efficacy varies by species.³

Biofumigation

The use of volatile compounds released by decomposing plant materials, such as brassicas, to suppress soilborne pests.

Degree-hours

A measure of cumulative heat exposure, calculated by multiplying the time above a threshold temperature by the temperature excess.

Disinfestation

The process of eliminating pests, pathogens, or weeds from soil or growing media.