Harness the sun's energy to solarize garden soil pests

By Staff
Steve Strong
July 28, 2004
As the heat of summer near its peak, spring planted vegetable gardens are beginning to play out. The harvest was less than hoped for by many growers this season, as a host of disease, insect and weed pests plagued everything from tomatoes to butterbeans.
Several of the most common garden pests are soil-borne and are problems that are likely to occur again the following growing season when the same crops are planted back in the same spot. July through September offers veggie gardeners a great chance to reduce soil-borne pests, and the strategy is as natural as the sun.
Solar rays from direct sunlight generate an awesome amount of radiant heat and energy, and soil solarization is a technique that effectively traps the sun's radiation and uses it to fry soil pathogens. Solarizing is as simple as spreading a clear sheet of heavy-grade plastic across a garden plot, and leaving it covered for at least six to eight weeks in midsummer.
Soil moisture is critical for solarization to work, and the garden should be waterlogged thoroughly before spreading the plastic sheeting. It is also essential to cover the plastic edges completely to create an airtight seal- use soil, bricks, old landscape timbers or whatever's handy.
Clear plastic is preferred rather than black or white sheeting, because the goal is to create a kind of greenhouse effect in the top layer of soil where weed seeds, fungal spores, and insects lurk. This "boil-in-bag" method of soil sterilization can generate temperatures over 140 degrees in the top six inches, enough heat to kill back populations of parasitic nematodes and even nut grass roots.
Bacterial wilt is just one of the many killer diseases of tomato and pepper that survives in the soil all year. And like other deadly soil-borne pathogens (fusarium wilt, southern blight, a number of various fungi), there are few chemical controls available. Solarizing is safe, earth friendly, and one of the only strategies to try when pesticides are not an option.
Deep tilling and double-digging methods can be used in combination with solarizing to effectively reduce white mold (southern blight) in the soil, and other problematic diseases that produce tough-to-kill spores. Again, the time of year to try solarization is very important, and daytime temperatures need to be in the 90s for several weeks for it to work.
Other non-chemical methods of pest control can be explored online at the MSU Extension Web site at www.msucares.com. An Organic Vegetable IPM Guide (Integrated Pest Management) is available, in addition to Non-Chemical Weed Control Options for Home Lawns. The Garden Tabloid, publication 1091 also has several pest control strategies mentioned for veggie growers.
For more information on home gardening contact your county Extension office. Soil testing services and pest diagnosis are available, along with a plethora of free publications on practically ever subject under the sun.