Tomato plants killed by soil-borne disease organisms

Use a water breaker to uniformly wet bed surfaces

Soil-borne pests tend to accumulate in intensively managed gardens. Traditionally, pesticides applied before planting have been used to control a variety of insect pests, weeds and nematodes. Although the treatments are effective, most people object to them because of their toxicity to animals and humans. Also, many soil-applied pesticides are restricted to use on certain vegetable crops.

If you are looking for a non-chemical method of soil-borne pest control, consider solarization, achieved by placing clear plastic film on moist soil during the summer. Plants often grow faster in solarized soil and produce higher yields, both of which are attributable to improved pest control and increased nutrient release from organic matter decomposition.

The plastic film allows the sun's radiant energy to be trapped in the soil. Soil temperature at a 2-inch depth can rise to 130°F, hot enough to kill many disease-causing organisms, nematodes, insects and weed seeds. Although soil solarization controls many weed species, it will not affect deeply rooted perennial weeds such as bermudagrass, johnsongrass and nutsedge (nutgrass). Use a herbicide before solarization to control perennial weeds.

Plant-available nutrient levels increase due to accelerated organic matter decomposition that occurs during solarization. Consequently, you will want to wait until after solarization to soil test. You may not need to apply fertilizer prior to planting your next crop. Also, pay close attention to soil salinity. Soluble salt levels increase with solarization. Consider leaching beds with water if reported soluble salt levels exceed 1000 ppm.

Before laying plastic film, prepare beds following the procedure outlined in the 'Seed Bed Preparation' section. Solarization is most effective if the seedbed is smooth and the plastic film rests snug against the soil.