Landa® Hot Water Pressure Washer
The Landa® washer unit I tested was purchased by the Mississippi Army National Guard, with the intention of using it for cleaning heavy equipment, as well as for non-chemical weed control. The unit cost approximately $25,000 new. The cost of operation is about $10/hour for gas and diesel. I tested the steamer on patches of cogongrass (Imperata cylindrica) on the Camp Shelby Training Site in southern Mississippi. Cogongrass is a hardy perennial rhizomatous grass from Southeast Asia, and is highly invasive in many parts of the world, including the US Gulf Coast region. Burning, herbicides, mowing, and mechanical methods have only limited effectiveness as control measures, so we were interested in if the steamer could be used to treat cogongrass. We thought cogongrass patches could be killed if we treated both the aboveground leaves and the belowground rhizomes with pressurized steam, especially if we could inject the steam below-ground to kill those rhizomes. The Landa® steamer may be able to inject steam belowground, since we equipped it with a 0-degree pressure spray nozzle (this means the steam is delivered in a very concentrated stream, versus in a spreading, fan-shaped pattern). This intense stream of steam can penetrate ground to an average depth of 7.5-12.5 cm (3 to 5 inches).
The steamer in action
The Landa® washer works by using a gasoline engine to draw water from an 1,100 liter (300-gallon) reservoir into a small heating tank, where it is heated by a diesel burner unit. Pulling a trigger on the pressure wand activates the burner, but we experienced trouble with the burner not functioning on demand, resulting in nozzle temperatures being significantly lower than expected. A pre-shipping performance test performed at the factory documented a steam temperature of 118 degrees C (245 degrees F) and a pressure of 4.1 MPa (600 psi). A bypass valve may be activated to decrease pressure and increase temperature.
I used the steamer on 12 patches of cogongrass along roadsides in Camp Shelby, on 24-25 March, 2003. Average patch size was about 7 square meters. Treatments consisted of steaming for 1, 2, and 4 minutes per square meter, and 4 control plots that received no steaming. Steaming killed nearly all aboveground vegetation and the smell of cooking vegetation was apparent. Plots were revisited on 5 May 2003 to count number of tillers (stems). The 4-minutes per square meter treatment yielded a statistically significant reduction in cogongrass tillers, as compared to the control plots and other treatments. This might be due in part to the increased penetration of steam into soil in this treatment, which might have killed some rhizomes. It is also possible that the physical disturbance of squirting a very high-pressure stream of water/steam into the soil mechanically damaged the rhizomes, independent of its heat effects. Despite the immediate reduction in number of live tillers, new tillers began emerging shortly after steaming in all treatments. We speculate that this means:
1. That the Landa® washer was not effective in raising soil temperatures enough to kill the rhizomes, or
2. That cogongrass may be relatively resistant to heat damage, since the steam failed to effectively kill those stout rhizomes.
Close-up of steam-jet & mud!
The steamer, when functioning properly, delivers a jet of very hot, pressurized steam capable of inflicting severe burns. Aside from the thermal menace, the 0-degree nozzle emits a powerful, concentrated jet of water capable of cutting through flesh. Personal protective gear should include a full-face shield, hat, thick rubber gloves, rain pants, rain jacket, and rubber boots. Hearing protection is also needed, as the gasoline engine is quite noisy. Beware of copious back-splashing of extremely hot mud. This is not a good activity for hot weather, as heat exhaustion is a distinct danger, especially while suited-up in protective gear.
Advantages of the Steamer
- No risk of inadvertently starting wildfire
- Since there are no residual chemicals, could be used in areas otherwise unsuitable to herbicides
- Targeted kill to only those plants which have been steamed; although it can be difficult to direct steam if desirable plants are thoroughly mixed in with the weeds
- Requires no permits, licenses, etc.
- Effective at killing seedlings and annual plants
Disadvantages of the Steamer
- Is less effective when used against plants with extensive underground roots or rhizomes
- Can only reach vegetation on or near roadsides
- Must be refueled and refilled with water every 2-3 hours of continuous operation
- Very expensive to purchase
- Unintentional, undesirable effects from using below ground are currently not well understood
- Problems with temperature, because of trigger-activated burner not switching on
- Risk of burns
- This is a very hot job, not suited for warm weather use
The weed steamer probably works best on weed species without extensive rhizomes. It may be a very good tool for cleaning heavy equipment of weed propagules to prevent spread to other sites, the major mode of dispersal for cogongrass in our area.
For information on Landa® pressure washers contact:
4275 N.W. Pacific Rim Blvd.
Camas, WA 98607 USA
Landa® web site
For more information on this experimental use of the steamer contact:
The Nature Conservancy
Camp Shelby Training Site-ENV, Bldg. 6678
Camp Shelby, MS 39407-5500
--Author and Photographer: Robin Switzer, TNC-MS, March 2004
--Edited by Mandy Tu, Barry Rice, TNC/GIST