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David L. Mausel Forest Health Forester, Menominee Tribal Enterprises –Forestry Division PO Box 10, Neopit, WI 54150

Mary Bartkowiak Invasive Plant Specialist, Wisconsin Department of Natural Resources, Forest Health 107 Sutliff Ave., Rhinelander, WI 54501


Vehicles and mobile equipment are recognized pathways for the spread of invasive plants in forests; yet washing them is not in common use today, despite its being a cost-effective preventive tactic. We report on the operational practice of washing, the development of best management practices, and observations on intercepted plant species in the managed forests of the Menominee Indian Tribe of Wisconsin. A commercially available vehicle undercarriage wash system was used to wash street-legal vehicles, and pressure washers were used to wash mobile equipment. The soil washed from street-legal vehicles was collected and placed in raised beds and left for one year to permit the seeds to germinate and emerge for identification. A total of 48 species of plants from 18 families were intercepted via vehicle washing, 42% were non-native plants and 11% were invasive plants. Best management practices were developed for several user groups with the goal of minimizing the unintentional spread of invasive plants.

KEYWORDS: Invasive species, prevention, vehicle washing, human-mediated dispersal, weed seed spread, propagule pressure


Vehicles, mobile equipment, and even footwear are recognized pathways for the invasion of environmentally detrimental invasive plants in terrestrial ecosystems (Ware et al. 2012, Bajwa et al. 2018, Rew et al. 2018). In managed forests, for example, accidental introduction of such plants and their spread by humans is undoubtedly due to vehicles, mobile equipment, and materials accompanying recreational users, foresters, wildland firefighters, road crews, logging operations, site preparation, and planting activities. Preventive washing of vehicles and mobile equipment that travel to forests is a well-intentioned integrated weed management tactic, but this is expensive, logistically challenging, and difficult to enforce, and consequently is not in common use in the United States other than during fire management by the USDA-Forest Service, (Trent et. al. 2002, Fleming 2008) and the US military (Rew et al. 2018).

On the Menominee Indian Reservation in northeastern Wisconsin, which con


sists of 235,560 acres, 87% of the land is under sustained yield forest management, and this long-term stewardship has enabled the land to remain an unfragmented remnant of the prehistoric Lake States forest. The 2,573 miles of unimproved dirt roads distributed throughout the reservation, most of which were built between 1930 and 1950, are open only to enrolled tribal citizens, Menominee Tribal Enterprises (MTE) forestry and road crew vehicles, 25 logging businesses, various Tribal departments, and invited visitors. Unfortunately, these roads also are a pathway for invasive plants. However, despite over 160 years of forest management, the reservation is relatively uninvaded compared to the other areas of the upper Midwest and eastern US (Oswalt et al. 2015), largely due to minimal development and other changes in land use. Furthermore, of the 112 terrestrial invasive plant species that are regulated by the State of Wisconsin (Wisconsin Administrative Code 2017), only 28 are known to exist within the reservation. Due to the increasing abundance in the region of invasive plants that threaten the reservation, it became a priority for MTE to prevent further introductions and spread from vehicles to protect the ecological integrity of this nationally renowned forest.

MTE, which is the forestry and lumber mill business section of the Tribe, began in 2016 to develop best management practices for the washing of all forestry related vehicles and mobile equipment as a component of their integrated weed management program. To accomplish this for mobile equipment, pressure washers were purchased to clean ATVs, UTVs, road graders, backhoes, dozers, roller choppers, anchor chains, a Bracke planter, forwarders, skidders, drags, and processors. A pressure washer is permanently installed at the MTE Forestry Center offices in Keshena, Wisconsin, and a mobile pressure washer is mounted on a water tender truck. For street-legal vehicles (SUVs, light-duty trucks, wildfire engines, gravel trucks, log trucks, and trailers) a commercially available wheel and undercarriage wash was permanently installed at the lumber mill in Neopit, Wisconsin. At peak activity, over 70 log trucks and other vehicles enter the mill yard each day hauling logs and on other business.

To make progress towards the goal of minimizing the spread of invasive plants, our objectives were to establish a washing program, develop best management practices, and observe what plants are being spread. There is a need to assess if this washing program is logistically feasible at an operational scale in forest management, and to justify the effort by observing which species of plants are being unintentionally spread.


To wash mobile equipment (e.g., logging equipment), a SC30008DAF diesel pressure washer on a mobile skid, manufactured by Hydro Tek Systems Inc. of Redlands, California, was mounted on a 1993 Ford L8000 water tender with a 1000-gallon tank (Figure 1). Key to the efficient performance of this system is its ability to be operated by one person (although there are two spray wands that could be used), its ability to reach high pressures, and its hot water capabilities (up to 200° F) that can be used if needed to remove tough deposits.

To wash street-legal vehicles, a Moby Dick Quick 732 wash unit (Frutiger Company AG, Winterthur Switzerland) was opened on August 23, 2016 at the MTE lumber mill for use by authorized drivers. Key to the performance of such a system is automated operation for the drivers to pass


FIGURE 1. A pressure washer mounted on a 1000-gallon water tender is used to clean a for

warder before transport to the next cutting unit to prevent the spread of invasive plants.

through, water recycling, and a system to collect debris removed from the rinse water. The wash platform is 9.5 ft wide and 24.0 ft long allowing for two full rotations of log truck tires over a ramp with integrated water nozzles (Figure 2). The weight limit is 33,069 lbs/axle. Water is pumped from a 10,000-gallon supply tank and is sprayed on the sides and undersides of the vehicles under low pressure and high volume to dislodge soil deposits, organic matter, and plant propagules that have accu-

FIGURE 2. An automated wash system is used to clean the wheels, wheel wells, bumpers, and undercarriage of pick-ups, SUVs, log trucks and trailers, wildfire engines, and gravel trucks to prevent the spread of invasive plants. The wash platform is 24 feet long, allowing for two full rotations of tractor trailer tires over a ramp and side-bars with integrated water nozzles.


FIGURE 3. Raised beds were used to grow plants from the soil deposits, organic matter, and

plant propagules washed from 846 vehicles in an automated wash system from September

through mid-November 2016.

mulated on the wheels, wheel wells, bumpers, and undercarriage. Rinse water flows back to the tank, where alum flocculent assists in the settling of the fine particles to the bottom of the tank. Three coarse filters made of sheet metal were added to the tanks to keep bark out of the pumps. A scraper conveyor removes the debris from the bottom of the tank and deposits it in a wet particulate matter collection bin for burial at a landfill. For detailed washing of light-duty trucks, SUVs, ATVs and UTVs, wildfire engines, and miscellaneous forestry equipment at the Forestry Center, a pressure washer (model 2SF22ESI.AHE), manufactured by Cat Pumps of Blaine, Minnesota, is available for use.

Instead of disposing it in a landfill, from September through mid-November the soil from the automated wash system was placed into outdoor raised beds (Figure 3). During this time period, the washer’s event recorder indicates that it had washed 846 vehicles. The raised beds were unshaded and had approximately 8 inches of soil spread out over 344 square feet. After overwintering, the seeds in the soil germinated and plants emerged during the summer 2017 growing season. InAugust 2017 plants were collected, identified, and categorized as native, non-native, or invasive species. Invasive plants are defined as non-native species that cause ecological or economic harm, or harm human health.Voucher specimens were deposited in the Freckmann Herbarium at the University of Wisconsin-Stevens Point (UWSP).


A total of 48 species of plants (five of which were identified only to genus) from 18 families were washed from the vehicles and identified in the beds (Table 1). Three of the five plants identified to genus only were in genera that have both native and non-native species in Wisconsin; accordingly, their status could not be determined. Of the remaining 45 species, 21 were native plants (representing 47% of the total), 19 were non-native plants (42%), and five were invasive plants

Page  82 TABLE 1. Native, non-native, and invasive plants that emerged from soil deposits, organic matter, and plant propagules cleaned from vehicles in an automated wash system.

Taxon Family Common name Status Life-form Seed type

Acer rubrumL. Sapindaceae red maple native tree samara Achillea millefolium L. Asteraceae yarrow native forb cypsela Agrostis giganteaRoth Poaceae redtop non-native graminoid caryopsis Ambrosia artemisiifoliaL. Asteraceae rag-weed native forb cypsela Arctium minusBernh. Asteraceae burdock invasive forb cypsela Bidens frondosaL. Asteraceae common beggar-ticks native forb cypsela Carexsp. Cyperaceae sedges unknown graminoid achene Cerastium fontanumBaumg. Caryophyllaceae mouse-ear chickweed non-native forb capsule Chenopodium albumL. Amaranthaceae lambs quarters non-native forb achene DigitariacognataSchuly.) Pilg. Poaceae fall witch grass native graminoid caryopsis Digitaria ishaemum(Schreb.) Muhl. Poaceae smooth crabgrass non-native graminoid caryopsis Digitaria sanguinalis(L.) Scop. Poaceae hairy crab grass non-native graminoid caryopsis Echinochloa muricata(P. Beauv.) Fernald Poaceae barnyard grass native graminoid caryopsis Eragrostis pectinacea(Michx.) Nees Poaceae tufted love grass native graminoid caryopsis Erigeron strigosus Wild. Asteraceae daisy fleabane native forb cypsela Euphorbia maculataL. Euphorbiaceae spotted sandmat native forb capsule Fallopia scandens(L.) Holub Polygonaceae black bindweed native forb achene Fragaria vescaL. Rosaceae woodland strawberry native forb achene Galeopsis tetrahitL. Lamiaceae hemp nettle invasive forb nutlet Galinsoga quadriradiataRuiz & Pav. Asteraceae quickweed non-native forb cypsela GypsophilamuralisL. Caryophyllaceae baby’s breath invasive forb capsule Lepidium densiflorumSchrad. Brassicaceae peppergrass non-native forb silicle Leucanthemum vulgareLam. Asteraceae common daisy non-native forb cypsela Matricaria discoideaDC. Asteraceae pineapple-weed non-native forb cypsela Medicago lupulinaL. Fabaceae black medick non-native forb nutlet like legume Melilotussp. Fabaceae sweet clover invasive forb nutlet like legume



Mollugo verticillataL. Molluginaceae carpet weed non-native forb capsule Odontites vulgaris (Bellardi) Dumort. Orobanchaceae red bartsia non-native forb capsule Oxalis strictaL. Oxalidaceae yellow wood sorrel native forb capsule Panicum capillareL. Poaceae common witch grass native graminoid caryopsis Panicum dichotomiflorumMichx. Poaceae fall panic grass native graminoid caryopsis Persicaria maculosaGray Polygonaceae spotted lady’s-thumb non-native forb achene Persicaria punctata (Elliott) Small Polygonaceae smartweed native forb achene Phleum pratenseL. Poaceae timothy non-native graminoid caryopsis Plantago rugeliiDecne. Plantaginaceae red-stalked plantain native forb capsule Poa palustrisL. Poaceae marsh blue grass native graminoid caryopsis Polygonum achoreumS.F. Blake Polygonaceae leathery knotweed native forb achene Polygonum ramosissimumMichx. Polygonaceae bushy knotweed native forb achene Setaria pumila (Poir.) Roem. & Schult. Poaceae yellow foxtail non-native graminoid caryopsis Silene latifoliaPoir. Caryophyllaceae white-cockle non-native forb capsule Solidagosp. Asteraceae goldenrod unknown forb cypsela Trifolium arvenseL. Fabaceae rabbitfoot clover non-native forb nutlet like legume Trifolium pretenseL. Fabaceae red clover non-native forb nutlet like legume Trifolium repensL. Fabaceae white clover invasive forb nutlet like legume Verbascumsp. Scrophulariaceae mullein non-native forb capsule Verbena bracteataLag. & Rodr. Verbenaceae prostrate vervain native forb nutlet Verbena urticifoliaL. Verbenaceae white vervain native forb nutlet Viciasp. Fabaceae vetch unknown forb legume


(11%). The non-native plants are common weeds that cause little damage; however the invasive species are of ecological concern by outcompeting native species. For example, Galeopsis tetrahit L. (hemp nettle) is a legally restricted species in the State of Wisconsin, although it was already known to exist on the reservation. We expected that the most troublesome invasive forb spread by humans on the reservation, Alliaria petiolata (M. Bieb.) Cavara & Grande (garlic mustard), would be observed but it was not. Perhaps, it will emerge from the seed bank as monitoring continues in the future.

The dominant plant life-forms were forbs (73%) and graminoids (25%), although one tree (2%) was observed (Table 1). The seed types picked up by vehicles were diverse and were typically small seeds. Because the raised beds were outdoors, there is a possibility that some wind-dispersed seed germinated in the plots or grew through the mud from the gravel below. We would recommend a soil weed barrier and screening to prevent these potential sources in future studies, or use of a greenhouse.

Invasive plants are increasingly causing negative impacts to native ecosystems and confounding forest management activities (Liebhold et al. 2017). Because stronger preventive tactics are needed, best management practices related to vehicle and mobile equipment washing for MTE have been developed (Table

2) based on the assumption that washing is the most cost-effective method of invasive plant management. Results from these operational trials indicate that this activity is a worthwhile effort which is not financially or logistically impossible to implement. A few minutes of preventive action can protect the forest for generations to come. Feedback from log truck drivers indicated that they appreciate that the washing is fast and that they don’t have to exit their truck. They like to use the wash to keep their trucks clean for highway patrol inspections, maintenance, and pride. Some truckers thought the width of the unit is too narrow, but this was not a concern for all drivers. Challenges for the future include the re-routing of log trucks in the mill yard to make passes through the wash more convenient for the drivers and a compliance system to increase usage. Furthermore, the amount of species being introduced and spread is likely much larger than that described here, as other pathways of species introduction exist, such as animals, birds, wind, footwear, clothing, mower decks, and scientific equipment. Of particular concern is privately owned cars and light-duty trucks, and it would be desirable to install a smaller undercarriage wash in a non-industrial location in the future. The use of preventive washing is an option for land managers to implement and ideally integrated into holistic biosecurity plans incorporating the prevention of introductions of invasive plants as well as insects, pathogens, and other organisms.


Many thanks to Derrick White, Leon Fowler, Sapatis Webster, Clifford Kaquatosh, and Pershing Frechette for help with planning, building, and maintaining the truck wash and to Dr. Robert Freckmann for assistance with plant identification. Helpful comments on an earlier version of the manuscript were provided by the editor and an anonymous reviewer. Funding was provided by the Bureau of Indian Affairs, Noxious Weed Eradication Program.


TABLE 2. Best management practices for vehicle and equipment washing developed for Menominee Tribal Enterprises to prevent the invasion and spread of invasive plants. Washing is not required during the low-risk period between freeze-up and break-up.

Street-legal Vehicles (automated truck wash)

Required washing

• All log trucksdriven on off-reservation logging jobs beforedriving on reservation forest roads • Vehicles driven from off-reservation by official MTE visitors, such as government agency employees, research scientists, inventory crews, and tour participants if their vehicles will be going on main haul roads or logging roads • Pre-planned fire equipmentbrought in to assist with fires, prescribed and initial attack, before driving on forest roads. In addition, these vehicles can be manually pressure washed at the Forestry Center, if needed (They should be cleaned at their stations or en route) • MTE fire vehicleswhen returning from off-reservation details if they are not cleaned en route • Forestry, Fire Management, and Roads Dept. trucks and SUVs whenever passing by the mill, when muddy, or after having worked in or near a garlic mustard infestation. This should not totally replace occasional detailed pressure washing • MTE lumber delivery truckswhen returning from off-reservation if they went off pavement Voluntary washing

• All tractor trailersafter unloading each load of logs or bolts at the mill from on-reservation log jobs (bark should be swept from trailers before washing) • Tractor trailers hauling pulp loads to off-reservation mills do not need to go to the MTE mill for washing if it’s out of their way • Tractor trailers being used to buy logs from the MTE millyard • Initial attack resources called in to assist on a going fire (They should be cleaned at their stations or en route) Off-road Machinery (pressure washing)

Required washing (Equipment owned by MTE departments or contractors)

• Loggers—Processors, skidders, forwarders, drags • MTE Forest Development—Grapple skidder, anchor chain, roller choppers, Bracke planter • MTE Fire Management1—Engines, skid steers, UTVs, bulldozers, trailers • MTE Roads Dept.2—Bulldozers, front end loaders, graders • MTE Forestry Depts.— Trucks, SUVs, UTVs, ATVs, trailers Washing policy

• Any equipment that is brought onto the reservation must be thoroughly power washed and free of all plant material and soil or entry will be denied upon inspection • Any equipment that is moving (e.g., walking or via trailer) from one compartment to another compartment within the reservation must be thoroughly power washed and free of most plant material and soil a. The operators of the machinery and equipment should make an effort to remove large accumulations of plant material and soil with hand tools to make the power washing faster and more effective b. Washing of equipment must occur on a landing or road-side before the equipment is moved to another compartment • Washing is required when equipment is moved from storage to spring or summer jobs after the winter season 1 Resources called in for a going fire should be cleaned ahead of time or en route. If fire-fighting work on a going fire must move from one compartment to another, washing is exempt. 2 Graders are exempt from the washing requirement when working in the traveled way of main haul roads, but should be washed periodically at the shop.



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