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Waipuna™ Hot Foam System

Out of a New Zealand company named Waipuna™ comes this hot foam system for steam-killing vegetation. This system employs hot foam to deliver and trap superheated steam onto foliage to kill weeds. Waipuna™ states that the surfactant foam is a biodegradable mixture of corn and coconut sugar extracts, and that the foam is an "organic," naturally-occurring compound. As such, it is not regulated (or labeled) as a herbicide product by the U.S. EPA.

The Device and How it Works
The Waipuna™ Hot Foam system is comprised primarily of a diesel-powered boiler and foam generator, which deliver hot water with a foam surfactant to target weeds via a supply hose and a treatment wand. The superheated hot foam is applied to the targeted vegetation at a precise temperature (93 degrees C, 200 degrees F) and pressure; the foam traps the steam, giving it time to "cook" or "blanch" the vegetation. This causes a cellular collapse of the treated aboveground vegetation. The information from Waipuna™ claims that the hot foam can kill both annual and perennial weeds by starving their root systems (although for some perennials, repeat treatments may be necessary).

In addition to the boiler/burner-foam generator system, applicator hose and wand, the Waipuna™ system also includes an internal computer that monitors the flow and pressure of all functions. To make the system fully operational, however, you will have to provide the following additional equipment:
  1. A truck or minivan to transport the Waipuna™ system (a 2-ton flatbed truck works well)
  2. A large water tank - a 1,140 liter (300-gallon) baffled tank is recommended
  3. Foam concentrate solution - purchased by the barrel (100 liter/55 gal) from Waipuna™ (costs given below)
  4. Insulated hoses - 60 meters (200 ft) in length
Waipuna™ on a truck
Applying foam

There are two types of foam systems currently available: a single- or a double-burner version. Both are designed mostly for municipal use. The single-burner model is designed to be used by a sole operator (comes with one applicator wand), and can be mounted on the back of a trailer or truck. The double-burner model is to be operated by two people (comes with two applicator wands), and requires a minivan or large truck to transport. Waipuna™ states that the double-burner model is the most cost-effective method. A mechanical boom can also be used with the double-burner model. Waipuna™ plans to have smaller garden-use machines available in 2004.

Field Demonstration
To see how well the Waipuna™ system works in the field, I tested a double-burner model during a demonstration given by Oregon Bureau of Land Management (BLM) staff on the perennial rhizomatous grass, Brachypodium sylvaticum (false brome). After all tanks were filled and the hoses unrolled, the Waipuna™ system was turned on and heated up. The foam was ready to be deployed!

The system is noisy (about as loud as a deep-toned snowmobile or jetboat), but was very easy to use once everything had been set-up. To release the hot foam, you depress a small trigger on the application wand (which looks like a vacuum cleaner nozzle). This releases a constant stream of hot foam/steam (which came out much faster than I expected!). You simply draw the nozzle over any target vegetation to achieve good coverage of foliage with the foam. The hot foam achieves full kill on annuals immediately after contact. Some perennials can also be killed after only one treatment, but perennials with extensive root and rhizome systems may need to be treated several times for full kill. Tom Kaye (Institute of Applied Ecology) reports good kill results of using the Waipuna™ only once on B. sylvaticum patches, as does Janet Klein of the Marin Municipal Water District on Genista monspessulanus resprouts. The success of the Waipuna™ system on these perennials is interesting and promising, but it is unknown how effective the system would be against other resprouting species with deep, extensive root systems, such as with Tamarix spp., Euphorbia esula, or Lepidium latifolium.

Costs to Use the System
As of this writing (March 2004), the Waipuna™ system is not available for individual purchase. To obtain a Waipuna™ system, you must lease the system from the company for about US$700 per month (minimum lease period is 2 years).

Chuck Fairchild (BLM-Oregon) notes that the foam concentrate costs about the same as RoundUp® herbicide, since a 100-liter (55-gallon) drum of the foam concentrate costs about $900. Because of the equipment lease and costs of foam, however, Chuck estimates that the overall cost of using the Waipuna™ system is approximately three times that of using herbicide. He figures that treatments of open areas can take 20 to 25% longer than treating the same area using herbicide because of application equipment differences and equipment maintenance (filling water tanks, etc.). Although using this system is more expensive, Chuck adds that a big advantage of using the hot foam (instead of herbicide) is that the foam can be applied in variable weather conditions. Hot sunny weather is ideal for treatment, but windy cool moist (light rain) weather will also work. Further, depending on state pesticide regulations, an application permit is likely not needed when using this system.

Janet Klein (Marin Municipal Water District, California) has tried the Waipuna™ system on resprouts of French broom (Genista monspessulanus) and reports great results from using this tool. She applied the hot foam to broom resprouts (mowed first) which were mostly 2-3 years old and about 0.5 m (1-2 ft) tall, and found that the hot foam was very effective at killing the broom plants. She even tried applying the hot foam to a few older shrubs that were 1 to 1.5 meters (3-5 ft) tall with multiple stems and with thick root-stocks, and found that the Waipuna™ effectively killed those shrubs. Janet also tried the Waipuna™ on a few patches of invasive periwinkle (Vinca spp.), but did not see good kill results, perhaps because they did not treat the entire patch thoroughly. Janet estimates that the Waipuna™ system has cost them between $45,000 to $50,000 for the 2-year period. She finds it to be a useful tool for weed control in accessible areas, but adds that the Waipuna™ system is cost effective only if it is in near-constant operation year-round.

Pre-treatment and Post-treatment photographs
(Provided compliments of Janet Klein)
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Genista monspessulanus resprouts, 0.5 m tall;
March 20, 2003 (left) and April 23, 2003 (right)
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Foam applied to 1-1.5 m high Genista monspessulanus;
March 20, 2003 (left) and March 25, 2003 (right)
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Genista monspessulanus resprouts and Allium spp.;
March 20, 2003 (left) and April 23, 2003 (right)

A compendium of costs to use the Waipuna™ system includes:
  • Waipuna™ machine lease (Waipuna™ machine, foam generator, wands) - $700/month
  • Foam concentrate - $900 per 100 liter (55 gallon) barrel. If you were to use a 1,140 liter (300 gallon) water tank, you would add 4 liters of foam concentrate. A barrel of concentrate should last through 1 year of near-continuous use.
  • 1,140 liter (300 gallon) water tank - This allows two applicators to run the machine for about 1 hour before it must be refilled with water (it goes through water fast!). A 1,140 liter tank can cover about 0.6 km (0.4 mile) long swath on each side of road (about 1.5-3 m deep/5 to 10 ft deep), with solid weed infestations. If the roadside infestation is patchy, you may be able to cover about 6 km (4 miles) of road per day.
  • Diesel gas for Waipuna™ machine - 19 liters (5 gallon) tank; can last 3 days of treatment
  • Gas for generator
  • Gas for transportation

Protective clothing and gloves are recommended when using the Waipuna™ system. The foam can cause eye irritation. The foam should also not be applied to surface water, as concentrations of foam at 3 mg/liter can be toxic to fish. When applied to soil, the foam is generally applied at concentrations of 0.0004 mg/liter and it is degraded by soil microorganisms within 28 days, so the foam is likely to be benign to soil organisms. The California Department of Pesticide Regulation has determined that the Waipuna™ hot foam surfactant is not a pesticide, so it does not require registration as a pesticide product.

Sidenote: Chuck Fairchild notes that Waipuna™ system uses metric/English fittings, which may be difficult to find/replace if any of the machinery needs to be fixed.

Advantages of the Waipuna™ Hot Foam system
  • No chemically-produced herbicides are used, so depending upon your location there may be no need for permits.
  • It can be used in windy or moist/light rain conditions (heavy rain may breakdown foam quickly and lower temperatures).
  • It can be very specific-as long as the target plants are spatially separated from the surrounding vegetation, the Waipuna™ system can be applied to a single plant or to a small population of plants, with little to no disturbance to the surrounding vegetation.
  • Seedlings or annual herbs are instantaneously killed. Some perennials may be killed after one application.
  • Results are instantaneous - the user can see wilted, cooked vegetation and the areas where the foam was applied.
Disadvantages of the Waipuna™ Hot Foam System
  • The system has a large start-up cost: Machinery lease, foam solution, 2-ton truck, water tank, hoses, gas for diesel generator, gas for transport, etc.
  • Depending on how often it is used, it can be expensive to operate.
  • It may not thoroughly kill deep-rooted plants or those with extensive rhizomes with one application; perennial plants with deep roots may require several treatments for full kill.
  • Depending on how intermixed the weeds are with desirable vegetation, it may be difficult or impossible to provide target-specific control.
  • The system uses water very quickly - a water source must be nearby for continual use.
  • Because of the 60 m (200 foot) hose, it can only be used in sites easily accessible and navigable by truck.
  • It is relatively noisy, may not be applicable in areas with sensitive animal populations.
  • The effects of the "organic" foam on the environment, while probably benign, have not been extensively studied.

The Waipuna™ Hot Foam weed control system is a large and expensive set of equipment. It may be a valuable tool for weed control in organic farms, near visitor centers, or where there are limitations on herbicide use (by law or by choice), and can be especially useful along roads or in other municipal areas. Its utility in wildland settings, especially isolated natural areas that pick-up trucks cannot easily access, however, is limited.

More Information:
For information on leasing and advantages of the Waipuna™ Hot Foam system, see their website.
For personal account information on the Waipuna™ system use in natural areas, contact:
Chuck Fairchild, Bureau of Land Management, Eugene, Oregon
541-683-6207; chuck_fairchild(at)or.blm.gov
- or -
Janet Klein, Vegetation Ecologist, Marin Municipal Water District, California
415-945-1192; jklein(at)marinwater.org

--Author: Mandy Tu, TNC/GIST, March 2004

--Edited by: Barry Rice, TNC/GIST

Updated January 2005
©The Nature Conservancy, 2000