Traditionally, U.S. winegrowers have relied on tillage or, more recently, cover-cropping for organic and sustainable weed control. Though these methods allow growers to avoid using chemicals in their vineyards, they have their drawbacks. Tillage, for example, can damage soil life and structure, resulting in a loss of valuable nutrients and organic matter. Cover crops may attract pests, delay ripening and compete with vines for nutrients and water.

A new thermal weeding machine, exhibited at November's Sustainable Ag Expo in Paso Robles, Calif., offers growers an alternative method for dealing with vineyard weeds. Unlike other thermal weeders, which use flames or environmentally friendly foam, this one controls weeds with boiling-hot steam.

Available in the U.S. market since last summer, the patented Alartus Stinger is an Australian import produced by D. J. Batchen, Pty. Ltd. Towed by a standard tractor or four-wheel drive vehicle, the Stinger ignites propane and water to gener-ate a superheated steam, which is applied to weeds with an adjustable extension arm that reaches under crop foliage.

When applied to a weed, the temperature from the moisture in the plant's cells rises, causing its cell structure to rupture and preventing nutrients and water from reaching stalks and leaves.

According to Stinger applications engineer Kevin Smith, steam weeding is a better option than flames. "Steam is about 10 times more efficient at heat transfer than flame," he says. "That's because water causes the heat to fall onto the weeds when heat just naturally wants to rise. Because water does a better job of transferring the heat, you don't have to go down the row as slowly--you can go two or three times faster. With that, you have less labor time on your tractor, and you use much less propane."

Steam is also safer to use than flame, since there is no risk of fire damage. "The temperature of the vine doesn't get much above 120ºF," Smith explains, "so it doesn't harm the vine or the drip system."

In addition to its use by about a half-dozen growers in Australia, the Stinger has been tested in vineyards in Washington state and California's Central Coast region. Smith has used the machine at Calcareous Vineyards and Pipestone Vineyard, both in Paso Robles.

Though he has seen good results in vineyard trials, Smith points out that the Stinger may not be the best solution for every grower. "I've found that it works much better on more mature vineyards," he says. "If you've got one-or two-year plants this is probably not your gizmo, because the canopy is a spring action thing that rubs up against the vines. It just puts a little too much pressure on the young vines."

For best results, Smith advises blasting the weeds with steam when they're 1-3 inches tall. "You want to spend some time adjusting the canopy so it's at the right width and the right angle. It just takes a little bit of set-up time to make sure that you're applying it at the right speed and height."

The Stinger sells for $25,000, which may seem pricey to some growers. However, Smith says the machine makes good economic sense in the long term. While working as an independent research analyst, Smith was commissioned to conduct an economic study comparing various methods of weed control in Central Coast vineyards. Smith looked at three traditional chemical programs, three sustainable "softer" chemical programs and an organic method: tillage.

"I found that the Stinger, on a per-acre basis, was less expensive than the 'soft' herbicides or mechanical/organic method," Smith says. "If you're farming 100-200 acres, you can save over $25,000 in four years."

Traditional chemicals, however, were the most inexpensive weed control option, since they only need to be applied once or twice per year. Both "soft" chemical and steam treatments require application four to five times per year.

Though traditional chemicals are less expensive than the other methods, Smith points out that they can lose their effectiveness over time. "Weeds tend to build tolerance to most chemicals; they don't tend to build resistance to 800° steam."

Steam weeders may have a few drawbacks of their own, however. According to a report by UC Davis Cooperative Extension weed ecologist W. Thomas Lanini, published on the Napa Sustainable Winegrowing Group Web site (nswg. org/tomlanini.htm), steam technology may not be effective for all weeds, and can be affected by factors like weed age, application speed and amount of steam applied.

The Stinger will be put through extensive testing later this year, when Cal Poly weed scientist Ramon Leon, Ph.D. launches a two-year study to test its effects on vineyards.

For more information, contact Kevin Smith at (805) 975-6541.