Improved Hot Water Weed Control System

The Waipuna system shown here consists of a computer controlled boiler combined with a diesel generator and a source of water.

On Nov. 9, 2000, Debby Raphael of the San Francisco IPM Program organized a demonstration of the new, improved Waipuna weed control system. At the core of the Waipuna system is a diesel-powered, computer-controlled boiler that delivers hot water to weeds through a supply hose and a treatment wand. Reservoirs of cold water complete the system. Both boiler and water containers are easily transported in a minivan to the treatment site. Water leaves the boiler at temperatures above the boiling point (212 F, 100 C) and exits on the ground at 208 F (98 C). Therefore, very little heat is lost through the 100-foot delivery hose, and boiling water is generated at the rate that it is used. Operators can literally "mop-up" weeds.

Though earlier versions of the system used only boiling water to control weeds, the new system generates a biodegradable foam from a mixture of corn and coconut sugars added to the treatment water. The foam produces a thin film that prevents heat from immediately dissipating as the hot water is released. When boiling water is applied to soil, at first heat is lost quickly, then surface temperatures stabilize due to the heat retention properties of the foam.

Without the foam, operators had to saturate the ground with hot water to get enough heat to do the job. Now they can get the vegetation wet with water and foam, then move on. Addition of the foam means that treatment of weedy areas can be accomplished twice as fast.

In areas around ornamental beds, underneath shrubs and other areas, the Waipuna system is just as fast as applications of glyphosate (Roundup®). Unfortunately, there is a limitation to how fast large, open areas can be treated. Treatment of open areas with the Waipuna system can take 20 to 25 percent longer than treatment of the same area with herbicides.

This technician is applying hot water and foam from the Waipuna system along a path for weed control.

HOW PRACTICAL IS THE SYSTEM? The mixture of corn and coconut sugars used to make the foam has the consistency of molasses. About 1 quart of the material is mixed with 50 gallons of treatment water (0.5 percent), and the polymerized sugars effectively act as a surfactant. Each 50 gallons or so of solution provides enough boiling water for about 15 minutes of operation. A minivan can carry enough water for about one hour of work. After this time, water containers must be refilled with new solutions of the surfactant. In practice then, operators get to take a break every hour to refill water containers. Water sources are usually conveniently available in municipal areas, but there could be some delay when the machine is used to treat roadside weeds along the highway.

COSTS. The cost of the surfactant is about the same as Roundup since a 55-gallon drum costs about $900. In the past, the Waipuna machine was available only through a leasing arrangement. Now the company will sell the machines outright. The basic machine has one boiler, and costs about $28,500 - about half a year's salary for one landscape worker. Cost of the machine varies with the number of boilers. The two-boiler machine, which works twice as fast, costs about $38,500.

Weeds covering this path are quickly "mopped up" with the Waipuna system.

The machine would be cost effective in school districts where pesticide use is forbidden. In the Los Angeles School District, for instance, the number of people employed in weed control has mushroomed from six to 37. The Waipuna machine could significantly cut back on labor costs in these big school districts. According to an Oct. 5, 2000, Wall Street Journal article, weeds bursting through asphalt on paved playgrounds are a common problem in the Los Angeles school district. The Waipuna van could be driven quickly to these areas and operators could spot-treat problem areas.

MUNICIPAL VEGETATION CONTROL. Municipalities that have pesticide bans or IPM ordinances may find the machine useful. Municipalities must control weeds growing in cracks of pavement, since uncontrolled weed growth breaks pavement open and leads to potholes and similar damage. The Waipuna system is used in New Zealand to control weeds around curbs and channels, footpath edges, driveways, boundaries and obstacles. When hot water is applied to weeds, all the aboveground foliage is thermally denatured and killed.

Weeds growing along this path have been stopped by the Waipuna treatment.

EFFECTIVENESS. The New Zealand Institute for Crop and Food Research tested the Waipuna system in 1992 and compared results with glyphosate (Roundup) applications. A block of kiwifruit at the Institute was the test site. The data showed the Waipuna system works faster than glyphosate, and had about the same effectiveness. After 49 days, no annual weeds had survived the Waipuna treatment, but a few perennials had regrown from taproots (Ingels 1992).

Target weeds in the test included annual bluegrass, Poa annua; perennial ryegrass, Lolium perenne; fumitory, Fumaria officinalis; buttercup, Ranunculus spp.; white clover, Trifolium repens; dandelion, Taraxacum officinale; scrambling speedwell, Veronica sp.; twin cress, Arabidopsis sp.; bitter cress, Cardaria sp.; broadleaf dock, Rumex sp.; sow thistle, Sonchus sp.; black nightshade, Solanum nigrum; creeping woodsorrel, Oxalis corniculata; bermudagrass, Cynodon dactylon; and field bindweed, Convolvulus arvensis (Daar 1994).

Normally, treated vegetation blackens and dies within 24 hours, but some species may take several days to show symptoms. The broader and thinner the leaf, the quicker the reaction. Treatments applied in hot, sunny weather are quicker than applications during cooler weather (Daar 1994).

Tough perennials may require retreatment. For instance, kikuyugrass, Pennisetum clandestinum, a perennial from South Africa, causes many problems in New Zealand. After kikuyugrass is treated, it begins to regrow within three weeks. A second treatment at 35 to 45 days delays growth up to 12 weeks. A third treatment stops regrowth for three to four months. Destruction of aboveground leaves, and prevention of photosynthesis reduces nutrients available in the roots, reducing regrowth (Daar 1994).

Areas around trees can be quickly treated without damaging the tree.

WAIPUNA SURFACTANT. Is the surfactant used in the Waipuna system safe for the environment? The surfactant, called alkyl polyglycoside, is formulated wholly from corn and coconut sugar extracts. The concentrate has the consistency of molasses and is chemically a polymer of glucose. Like soap and other surfactants used for laundry, the Waipuna surfactant will cause eye irritation. When handling the concentrated surfactant, gloves and protective clothing are recommended to avoid prolonged and repeated skin contact. The surfactant has low toxicity and an oral LD50 in rats greater than 5000 mg/kg.

According to company literature, about 1 mg of the foam is applied per kilogram of soil. The LC50 for the earthworm, Eisenia sp. is about 654 mg/kg, and thus earthworms are not threatened by the treatment. Detrimental effects to aquatic organisms are expected at concentrations above 10 mg/liter, although effects on sensitive organisms such as the water flea, Daphnia sp., and some fish will occur at lower concentrations. For instance, water concentrations of 1 mg/liter will inhibit reproduction of the water flea, a common test organism for aquatic toxicity. The material can be toxic to fish at concentrations of 3 mg/liter. Because of this, the foam should not be directly applied to surface water. According to company literature, the foam is applied for weed control to soil at concentrations of 0.0004 mg/liter and should be totally benign. When applied to soil, the foam is degraded by soil microorganisms completely within 28 days.

The California Department of Pesticide Regulation has determined that the surfactant is not a pesticide, and therefore does not require registration. Phillip Dickey of the Washington Toxics Coalition has rated the weed foam formula as among the safest of surfactants. The material has been approved by IFOAM for organic agriculture in Australia (Waipuna 2000).

Weeds around the tree have been killed by the Waipuna system. Weeds start to die within 24 hours.

DOMESTIC VEGETATION CONTROL. The hot water-surfactant weed control system is not the only good news from Waipuna. For homeowners and residents looking to control weeds of the lawn and garden, Waipuna has also developed an electric portable water heater called the Green Weeder. The Green Weeder is made from plastic in a wand shape that allows treatment of weeds without bending or crouching. It is a lightweight, hand-held device that targets weeds without damaging desirable plants. Using only tap water and electricity, the Green Weeder exposes plants to high temperature steam and water. The domestic weeder controls weeds in windy or wet weather conditions without posing a danger to prized plants or vegetables.

CONCLUSION. The Waipuna system provides a non-toxic alternative to chemical herbicides for weed control. School systems and municipalities that have converted to IPM methods or that have pesticide bans could successfully use the system as an economically viable alternative to herbicides. The major disadvantage of the method is that all treatments must be accomplished within 100 ft of the boiler and water supply.

Homeowners and others may find the small handheld model useful for lawn and garden weeds. The handheld model is limited only by the length of garden hose and electrical extension cord available. Hot water is very successful for control of annual weeds, but perennial weeds may have to be retreated on a regular basis to deplete food stores in the roots. Like any other weed management method, hot water and the Waipuna system should be used in a complete IPM program that includes prevention as well as positive controls.

RESOURCES

• Waipuna USA - 701 West Buena No. 3, Chicago, IL 60613; 630/514-0364; Fax 630/654-2380; email jeffw@waipuna.com.
• Waipuna International - P.O. Box 62140, Mt. Wellington, Auckland, New Zealand; 64 9 2765840; Fax 64 9 2760330; email wil@waipuna.com; Web site www.waipuna.com.

REFERENCES

• Ingle, A. 1992. Performance of the non-toxic vegetation control process. Crop and Food Confidential Report No. 3. New Zealand Institute for Crop & Food Research Ltd. Levin, NZ. 9 pp.
• Daar, S. 1994. New technology harnesses hot water to kill weeds. IPM Practitioner 16(1):1-5.
• Waipuna. 2000. Waipuna company literature. Contact: Waipuna USA or Waipuna International for a copy.

The author is an IPM specialist and executive director of the Bio-Integral Resource Center.