Herbicide Alternatives Research - Executive Office of Transportation

Mowing. Clearly, the most common cultural practice employed along roadsides is mowing,
particularly in Zone 2, the Safety Clear Zone. The frequency and height of mowing varies from
one state to another. Connecticut and Rhode Island maintain a minimum mowing height of 3
inches. Mowing begins when vegetation reaches a height of 6 inches. Generally, this practice
results in mowing 2 to 3 times per year. New Hampshire mows grass areas along open highways
at a cutting height of 6 inches, but in more traveled areas near population centers, cutting height
is reduced to 2 inches (Giunta, 2004). For most New Hampshire highways, grassed areas are
mowed twice per year.
It is generally accepted that mowing high, at least 4 to 6 inches, can reduce stress on grass plants.
Mowing at high-cutting levels improves vigor of grass growth and reduces the frequency of
mowing to twice a year or less. High-cut grass also retards growth of weed species and hinders
the establishment of woody species. Gover (2003) suggested that too many highway managers
are overly concerned with the aesthetics of roadside plantings and mow too frequently at too-low
cutting heights. This perception, he contends, complicates roadside vegetation management and
interferes with the control of weeds.
Mowing is also the primary method for eliminating many invasive species that may establish in
Safety Clear zones.
Brushing. The Maine DOT does not favor mechanical methods such as bush hogging (mowing
of brush with heavy-duty, power-driven, rotary cutters). The 2001 report from the Maine DOT
(Moosman, 2001), stated that mechanical methods of brush control (mowing or bush hogging)
are more expensive than spraying and result in higher stem counts over time from regrowth of
brush if no treatment of cut stems is done. However, hand removal of brush (brush cutting) is
more expensive than mowing with the added issue of worker safety. Also, mechanical and handcutting
methods with the use of power equipment increase the potential for environmental risk
from fuels and oils (Moosmann, 2001). Maine is using a growth regulator, Krenite S (du Pont,
Wilmington, Del.), to control brush (Moosman 2003).
An example of an integrated vegetation management approach to brush control is described by
Gover et al. (2004). They describe mechanical, cultural, and chemical options for controlling
tree-of-heaven (Ailanthus altissima Swingle). Similar management options apply to species such
as black locust (Robinia pseudoacacia L.), sassafras (Sassafras albidum Nees.), and sumac (Rhus
typhina Turner) that occur along roadsides and that regrow readily form sprouts on cut stumps.
In a study investigating mechanical, chemical, and combination of mechanical and chemical
brush control in Ontario, Canada, Puttock (1994) concluded that cutting followed by the
application of herbicide to the cut surfaces or regrowth was the most cost-effective systems for
reducing the density and proportion of stems greater than one-yard tall.
Thermal. Principles of using heat to control weeds are discussed by Daar (2004). Currently
none of the New England states are using flame or steam-hot water techniques along highways.
However, Vermont has run trials using wet infrared thermal technology along railroad rights of
way (Burnham et al., 2003). This report notes that wet infrared thermal treatment exposes weeds
to high temperatures, thereby denaturing proteins and rupturing cell walls. The resultant injuries
disable normal plant functions and destroy shoots. The treatment can be effective in killing
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