by George Wooten, Winthrop, WA, November, 1999

The following outline is intended to help design and implement a comprehensive program of vegetation control. Such a program might be required in cases where large areas are involved, intractable species have invaded an area, control costs are potentially very high, or existing management techniques are ineffective or unacceptable.

I. Planning and technical analysis needs for a comprehensive vegetation control program.

A. Perform site analysis.
 
1. Be site specific.

2. Monitor ongoing projects and search for new invaders.

3. Use site indicator species to understand ecological amplitude (Quarles, 1999, Neal, 1993).
 

B. Consider invading species biology (Hobbs and Humphries, 1995, Hiebert and Stubbendieck, 1993).
 
1. Consider life form (annual, biennial, perennial, Quarles, 1999). With annuals and biennials prevention of seed formation is important; for perennials prevention of sprouting is important (Elmore, 1993a, Miller, 1975, Quarles, 1999).

2. Understand species performance (Luken, 1997, Marrs and Lowday, 1992). Some weed control methods can enhance the performance of new invaders, retarding establishment of desirable plant communities.
 

C. Analyze the disturbance regime (Quarles, 1999).

D. Identify operating systems and their controls.
 

1. Identify economic factors, e.g. cost / benefit ratios (Luken, 1997, p. 133).

2. Identify functioning and impaired biological and ecosystem processes.
 

a. Identify desired future conditions.

b. Identify biological and ecosystem control factors.
 

(1) Facililtation controls (late-successional species response to environmental modifications (Connell and Slatyer, 1977).

(2) Tolerance controls (late-successional species grow in the presence of early-successional species: Hils and Vankat, 1982, Walker and Chapin, 1987).

(3) Inhibition controls (late-successional species establish and grow only after early-successional species become senescent or die: Hils and Vankat, 1982, Walker and Chapin, 1987).
 

c. Identify effects of the proposed changes to the environment over time.


3. Identify management limitations.


E. Perform integrated analysis
 

1. Use an interdisciplinary approach to develop a broad range of reasonable options and alternatives, along with a realistic set of possible outcomes.

2. Look at the big picture. "Attempts to control weeds without addressing the causes of the invasion are
doomed because they treat symptoms rather than causes." - Hobbs and Humphries (1995). Avoid the urge to rush into a "crisis" situation, and instead, take time to plan a concerted effort to control invading species.

3. Use a decision-making system (Hobbs and Humphries, 1995, David Pimental, 1999, David Pimentel in Vandenburg, 1996).

4. Use ecosystem management (Daily et. al., 1999, Luken, 1997).

5. Use Integrated Pest / Weed Management (IPM, IWM).
 

F. Implementation.
 
1. Follow a timeline for achievement of goals.

2. Insure that proper timing of control methods occurs.

3. Monitor project and method effectiveness; include follow-up visits for the first three years.

4. Practice adaptive management. Have a back-up plan. Be prepared to adapt management to changes in expectations.

A.  Direct human intervention.

1. Mechanical methods of removal ("mechanical controls").

a. Hand-pulling ("manual control"). A new program of studies of the use and effectiveness of hand pulling to control noxious weeds has been instituted at the University of Colorado by Professor Tim Seastedt (Boulder Camera, 8/22/99).

b. Many specific tools exist for the control of specific invaders, such as the "Weed Wrench" type of implement (New Tribe, 5517 Riverbanks Rd., Grants Pass, OR 97527, 541-476-9492). Educate yourself about the proper tool for the job and avail yourself of it.

c. Mowing. A Colorado study (Lastoka Property, 1997-1998), found that mowing diffuse knapweed (Centaurea diffusa) reduced seed production 85% in 1997 compared to unmowed areas. Mowing also helps prevent tumbleweed production. Timing, plant height and blade sharpness may be critical factors (Sam Lucy, Winthrop, personal communication).

2. Physical methods of plant control.

a. Hot water / steam treatment (Waipuna International, Ltd. 1999, Chapel Hill Newspaper,  1999, contact Allen Spalt, Dir., Agricultrual Resources Center, PESTED, 115 W. Main, Carrboro, NC 27510, ph. 919-967-1886). The town of Carrboro, North Carolina is killing weeds with hot water from a special machine. The hot water removes the waxy cuticle coating plant leaves and stems, causing rapid death. The method is not plant specific, but can be made more effective through combination with a surfactant (Havey, 1999).

b. There was an article on p.28 of the May 19 Capital Press re: Greg Prull in
Eugene, Oregon, with a new "wet infrared" system for killing weeds.  Built
the first prototype in 1996.

3. Chemical methods of plant control.

a. Herbicide application. Herbicides work through several modes of action, including the inhibition of electron transport, growth regulation through auxin / cytokinin mimicry, amino acid synthesis inhibition, lipid synthesis inhibition, seedling growth inhibition, photosynthesis inhibition, cell membrane disruption, and pigment inhibition (Anderson, 1994). As in medicine, there is no "silver bullet" that will cure the problem without side effects. Herbicides remain general in their specificity, with a host of side effects and application problems. Claims of herbicides effective in extremely low quantities are merely more potent, and in fact such herbicides can be more hazardous in the case of spills. The utility of herbicides is not the subject of this paper; they are mentioned as a category for the sake of completion.

b. Herbicide amplification (not a desirable technique, in my humble opinion; see above - GW). An example of how herbicide use can be increased if pelletized seed is coated with an herbicide-absorbing charcoal layer (Clearwater Seed Company factsheet on Clearbon (TM) Seed Pellets, Clearwater Seed Company, Lewiston, ID. Still, the concept of using chemical absorbents has value as a control method. Charcoal produced in forest fires has been shown to absorb allelopathic chemicals produced by late-seral heathers, favoring the growth of early seral species.

c. Sunlight-activitated tetrapyroles ("Laser herbicides") can be applied to kill plants (developed by Univ. Ill. biochemist C.A. Rebeiz).

d. Cnicin, a knapweed extract is being tested under an EPA grant to the University of Colorado as a chemical agent to increase the effectiveness of biological control insects on knapweeds (Centaurea spp.).

e. Surfactants and wetting agents. Wetting agents have shown genuine effectiveness in weed control, although their use is primarily as adjuvants of herbicides. They have also been shown to increase the effectiveness of hot water treatments (Havey, 1999).

f. Corn gluten. In a recent comparison, corn gluten meal, a byproduct of the corn milling process, was more effective in garden weed inhibition than chemical herbicides (Consumer Reports, March, 1999). Corn gluten is also a source of nitrogen, but it has the disadvantage that it inhibits grass germination. Information is available at the University of Iowa.

g. Peach oil. Charles Wilson, a government scientist at the Agricultural Research Service's Appalachian Fruit Research Station in Kearneysville, W. Va. have found that the bencaldehyde in peach oil is effective at controlling fungal attacks (Rocky Mountain News, Mar. 14, 1999).

h. Pathogen attractants to encourage beneficial insects. Application of substances that enhance animal herbivory e.g., sugars, proteins, etc. (Grossman and Quarles, 1992).

B. Biological controls - through disruption of growth processes and reproduction.

1. Reproduction intervention.

a. Pollination controls. As a rule, invasive species tend to be generalist-pollinated, thus examples of successful control through pollinators is lacking. Encouragement of biologically diverse habitats, which
should have increased pollinator diversity, has been shown to be more drought-resistant, however the reason is still poorly understood.

b. Seed bank controls (Quarles, 1999, Luken, 1990, Luken, 1997). Many weed species produce large quantities of seed, which can survive in soils for centuries. Control of seedbanks is therefore an important and necessary control method in the management of invasive species.

c. Factors of seedbank quantity, quality and viability:

(1) Local vegetation sources.

(2) Seed germination rates.

(3) Seed decay rates and physical destruction of seeds.

(4) Seed predation.

(5) Reseeding efforts.

d. Reproductive spread of seeds and vegetative parts (see under prevention).

2. Allelopathy. Allelopathy is the production of plant growth and germination inhibitors by other plants has been documented in natural systems (Aldrich, 1987; Harrison and Peterson, 1991). The benefits of allelopathic plants has been documented (Schmidt, 1980; Jarvis et. al., 1985), as has the occurrence of allelopathic root exudates (Rice, 1987, Saggese, 1985). Controlled allelopathy is possible through planting of known allelopathic plants, application of the allelopathic chemcal or genetically modifying a plant to produce the allelopathic substance.

3. Genetic methods.

a. Hybridization - Invading species may evolve or adapt to a less pathogenic form over time. Occasionally adaptation is toward a more pathogenic form, but the observation has been repeatedly made that well-adapted invading species are less lethal to their host ecosystem, e.g., a parasite that kills its host ecosystem is not likely to be successful in the long run. This effect represents an interaction between the newly invaded ecosystem as well as within the invading organism.

b. Biologically engineered hybrids. Genetic engineering has the potential to change the fitness of invading species through genetic intervention, through the planned introduction of lethal mutations, sterile pollen, sterile or unfit seeds, etc.

C. Site modification.

1. Hydrologic regime. Availability of moisture, e.g., through irrigation, is perhaps the single most effective control measure for diffuse knapweed in Okanogan County, Washington (George Wooten, personal observation).

2. Soils.

a. Soil chemistry - amendments, fertilization.

(1) Nutrient availability and nutrient cycling is an extremely important consideration in the management
of invading species, which tend to be less dependent on specific soil nutrients.

(2) Soil pH. Many species favor high or low soil pH, e.g., blueberries and other Ericaceous species are acid-loving, whereas species such as some bluegrasses, junipers, etc. favor basic soils. Such amendments can favor desirable species, affecting vegetation dominance.

(3) Timing of fertiliziation encourages certain species (Deal, 1966).

b. Soil texture.

(1) Removal of rocks from soils can have a beneficial effect on ecosystem health. Rocks and rocky areas are drier microsites that absorb sunlight, and allow runoff to occur faster. Removing rocks from soils makes a site more homogenous, and soils are finer, benefitting certain species, e.g. bluegrasses, which can help outcompete weeds (George Wooten, personal observation).

3. Shading. Amount and timing of shade, and whether vegetation is deciduous or not is an effective tool for vegetation management (Elmore, 1993b).

4. Mulching. Examples of effective mulching controls

a. Straw mulch 3.5" thick gave 98 percent control of yellow star-thistle (Centaurea solstitialis) - Dremann (1996).

b. Greenwaste materials (Elmore, 1996).

c. Cover-cropping (Weston, 1996).

d. Synthetic mulches (Elmore and Tafoya, 1993; Walker and Prather, 1996). Recent studies show the synthetic mulches to be less effective than natural materials at reducing runoff (Cathleen Hapeman in Science News, Vol. 156 (1999).

e. Allelopathic mulching (Putnam and Weston, 1986; Altieri and Doll. 1978; Quarles, 1999).

5. Topographic factors.

a. Slope and aspect affect how water, sunlight and soil interact with an area. Slight changes in slope affect how weeds invade an area, e.g., cultivation of the Palouse loess results in flattening of soils through time, causing a more homogenous substrate for growth. Techniques such as terracing are widely used to grow crops on steep slopes.

D. Disturbance regime.

1. Soil disturbance.

a. Frequent cultivation can discourage perennials (Quarles, 1999).

b. Crop rotation discourages weeds (Dunham, 1973; Kempen, 1992).

2. Fire.

a. Controlled burns have a multitude of effects, including the death of trees, increases in shade, sprouting of shrubs and herbaceous perennials, temporary reduction in competition, changes in seed germination, and changes in nutrient availability, to name a few. Vegetation can be categorized as early-, mid-, or late-seral in respect to fire occurrences, and expected changes in vegetation make-up can be used to favor or disadvantage species makeup.

b. Flame weeding is an effective weed control method, it is inexpensive and is not labor-intensive. Flame weeders are available at hardware stores. The principle is to burst plant cells, causing loss of fluids and thermal denaturation. A further advantage is that mineral soil is exposed by the process.

c. Fire suppression is a factor that affects many forests, particularly in the interior western US. Effects of this anthropomorphic change to landscapes has both positive and negative aspects, including increased shading, increased dominance by late-seral species, increased competition for nutrients and sunlight, decreased germination, etc. Early-seral species, including many weedy ones, can be expected to decrease over time as an area revegetates following fire.

3. Climatic and diurnal factors.

a. Wind entrainment. Barrier or "snow" fences have been succussfully used to capture "tumbleweed" forms of weeds, preventing their spread, and allowing easier control by burning or plant removal.

b. Night-time cultivation. Germination of the seeds of some weedy species is enhanced by exposure to sunlight, which may signal the enzymes in the seed coat that the time is ready for sprouting. Night-time
tractor cultivation can cut weed infestations by 80 percent (Hartmann and Nezadal, 1990).

4. Protective measures. The use of set-aside preserves where management is minimal can have positive or negative effects on invasive species. In healthy ecosystems, there is a strong ecological "inertia" that can help maintain a weed-free system. In contrast, when left to themselves, some infestations, e.g. leafy spurge (Euphorbia esula), continue to worsen.

E. Ecological controls - factors influencing the interaction of species.

1. Plant competition.

a. Restoration grass seeding - Leafy spurge (Euphorbia esula) decreased 67 percent two years after grass seeding in Minnesota (Biesboer et. al, 1994).

b. Restoration plantings - used to control species make-up of an area.

c. Natural regeneration (Friedman 1987, Muller 1971, Hanawalt 1971) - useful in public forestry where money is available for silvicultural design considerations, and where revegetation processes can operate naturally.

d. Competitor enhancement - improving the chances for success of a competitor.

(1) Pruning of desirable species (Elmore, 1993a).

(2) Watering to benefit desirable species (Quarles, 1999). Water  infrequently and deeply to encourage depth rooting.

2. Animal controls

a. Regime - rotation, fencing, seasonality, etc. Grazing can have side-effect benefits and risks, including soil aeration, fertilization for the former, and unintended weed spread and soil disturbance for the latter.

b. Grazing system examples.

(1) Goats (Owsley, 1999; Nelson, 1999; Jackson, 1998). Angora goats reduced leafy spurge (Euphorbia esula) biomass by 44% in 3 years in North Dakota (Sedivic and Maine, 1993).

(2) Sheep. Five years of sheep grazing on experimental plots in Canada reduced leafy spurge (Euphorbia esula) by 93 percent (Johnston and Peake, 1960).

3. Invertebrate biological controls (Delfosse, 1994; Kelleher, J. S., M. A. Hulme, eds. 1984; Piper, Gary L. 1985). Many insect and microbial controls are now being developed by the USDA and universities. Research requires time and a quarantine before release, however both leafy spurge (Euphorbia esula) and the knapweeds (Centaurea spp.) have become the poster childs of a large USDA effort to bring them under control using several dozen insect and microbial agents. Such intensive programs will eventually succeed, as the originating countries of origin for most species have a large number of parasites. The research and release of agents carries with it the risk that unintended hosts will be attacked and decimated, and notable examples already indicate this has occurred. Although safeguards are thorough, not every native plant and growning environment can be tested.  Examples of invertebrate biological controls:

a. Natural insect enemies (Hobbs and Humphries, 1995).

b. Introduced invertebrate control species - examples.

c. Flea beetles (Aphthona spp.) reduces leafy spurge (Euphorbia esula) control from 4000 ac to 400 acres (Rocky Mountain News, 7/25/99, and cut states costs in half. In Alberta, Canada spurge was reduced 99% five years after release (Harris, 1991).

d. Root-boring insects (Delfosse, 1994).

e. Seedhead insects (Delfosse, 1994).

f. Musk thistle (Carduus nutans) control has shown promise using the head weevil, Rhinocyllus conicus.

g. Genetically altered (transgenic or designer) insects may eventually be introduced for weed control, but none are currently in planning stages.

4. Microbial biological controls.

a. T.W. Anderson at Montana State University in Bozeman has established field plots that indicate the microbe Sclerotinia sclerotinium is capable of controlling up to 90% of mature spotted knapweed (Centaurea maculosa). Although the soil-forne fungus has a broad host range that limits its release, it demonstrates that it may be possible to harness the auxotrophic control mechanism (Grossman, 1999).

b. The rust Puccinia lagenophora reduces groundsel (Senecio vulgaris) populations through photosynthesis reduction (Grossman, 1999).

III. Prevention methods. According to Missoula County Extension Agent Jerry Marks, "Prevention is the most important tool. We are constantly asked why we didn't control this [weed] 20 years ago." - article by Daryl Gadbow in Experts depend on mixture of methods to control weeds, The Montana Missoulian, June 23, 1999. Examples of prevention methods:

A. Prioritize new invaders.

B. Use signage along infested areas so that the public will avoid transporting weeds to and from those areas.

C. Seed transport, intentional and otherwise, may be the primary cause of the spread of invaders. Examples of how seed transport may be prevented or reduced include:

1. Contaminated seeding mixtures (Quarles 1999); use only 100% noxious-weed free seed.

2. Avoid contaminated hay. Use weed-free hay and grain pellets (Olivarez, 1995).

3. Avoid contaminated mulch.

4. Avoid contaminated topsoil (Quarles, 1999).

5. Avoid contaminated road gravels.

6. Avoid contaminated nursery stock (Quarles, 1999).

7. Avoid contaminated manure (Quarles, 1999).

E. Control road use through infested areas. Noxious weeds often grow along roadsides where the disturbance of the roadside environment is favorable to their growth. This enhances the spread of invaders along roads, exactly where the transport mechanism occurs, and also where their subsequent spread can do the most damage. Roadside weed control and prevention of spread should be a high priority for road managers.

F. Use quarantines and vehicle washing, e.g., of tractors, cattle and logging trucks that may have just passed through a weed-infested site and are planning to go to a new site.

G. Eliminate the cause, not the symptoms, of the spread of invaders, i.e., control soil disturbances such as logging, grazing, and mining, until weed spread is stopped.

A. Make a list of targeted user groups.

B. Provide weed identification information distribution at central locations.

C. Post public relations / media / local displays at central locations. Sponsor a "Weed of the Week" in a local newspaper.

E. Establish a weed sighting report form.

F. Sponsor research projects that study invasive species (Morrison, 1997). Projects should include a set of study goals; replicate sampling; randomization; controls; preliminary sampling; and sampling authentication. Projects might include setting thresholds for measurement; coherent problem questions; area division; appropriate sample sizes; data distribution tests.

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