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United States Department of Agriculture

Animal and Plant Health Inspection Service

Plant Protection and Quarantine

Review of Petition to Add Genetically 

Engineered Glyphosate-tolerant Kentucky Bluegrass to the 

Federal Noxious Weed Regulations

June 30, 2011

Emergency and Domestic Programs

Contact Person: David T. Kaplan, Ph. D.
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Introduction 

The Plant Protection Act (PPA, 7 U.S.C. 7701 et seq.), authorizes the Secretary of 

Agriculture to prohibit or restrict the importation, entry, exportation, or movement in 

interstate commerce of any plant, plant product, biological control organism, noxious weed, 

article, or means of conveyance if the Secretary determines that the prohibition or restriction is 

necessary to prevent the introduction of a plant pest or noxious weed into the United States or 

dissemination of a plant pest or noxious weed within the United States. 

The PPA defines “noxious weed” as “any plant or plant product that can directly or 

indirectly injure or cause damage to crops (including nursery stock or plant products), livestock, 

poultry, or other interests of agriculture, irrigation, navigation, and the natural resources of the 

United States, the public health, or the environment.” 

Under the authority of the PPA, the Animal and Plant Health Inspection Service (APHIS) 

administers the regulations in 7 C.F.R. Part 360, “Noxious Weed Regulations,” which prohibit or 

restrict the importation and interstate movement of those plants that we have designated as 

regulated noxious weeds in § 360.200 (the Federal noxious weed list). The Secretary of 

Agriculture has discretion in determining which plants should be regulated under these 

regulations. Generally, plants regulated as listed noxious weeds are those plants that are 

determined likely to be aggressively invasive, have significant negative impacts, and are 

extremely difficult to manage or control once established. If APHIS determines that a plant 

poses a level of harm that would warrant its designation as a Federal noxious weed, APHIS may 

place the plant on the Federal noxious weed list and regulate it under 7 C.F.R. Part 360.

This document provides APHIS’s review of a petition to list herbicide tolerant Kentucky 

bluegrass as a regulated Federal noxious weed under 7 CF.R. Part 360.

Background

APHIS does not currently regulate Kentucky bluegrass, Poa pratensis L., as a Federal 

noxious weed. In 2002, APHIS received a petition from the International Center for Technology 

Assessment and the Center for Food Safety (the petitioners) requesting that the Agency list in 

its Federal noxious weed regulations, two types of Genetically Engineered (GE) turf grass 

species (Kentucky bluegrass and creeping bentgrass) that are tolerant to the herbicide 

glyphosate. 

In 2003, APHIS completed a weed risk assessment (WRA) and determined that GE 

glyphosate-tolerant creeping bentgrass did not meet the criteria to be regulated as a Federal 

noxious weed. The Center for Food Safety challenged APHIS’ decision in Federal Court, which 

remanded the WRA back to the Agency in 2007. 
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APHIS now has prepared a new weed risk assessment (WRA) and has conducted a 

review of the petition, which is described in this document, to determine whether the Kentucky 

bluegrass species, Poa pratensis L., which encompasses both Kentucky bluegrass that has been 

genetically engineered for tolerance to the herbicide glyphosate and non-herbicide-tolerant 

Kentucky bluegrass, should be listed and regulated as a Federal Noxious Weed.

Noxious Weed Regulatory Program History

The Federal Noxious Weed Act (FNWA) was passed in 1974 to establish a USDA program 

to address weeds that were having significant impacts on both plant and animal agricultural 

operations. The Act allowed USDA to regulate as a noxious weed “any living stage (including 

but not limited to, seeds and reproductive parts) of any parasitic or other plant of a kind, or 

subdivision of a kind, which is of foreign origin, is new to or not widely prevalent in the United 

States, and can directly or indirectly injure crops, other useful plants, livestock, or poultry or 

other interests of agriculture, including irrigation, or navigation or the fish and wildlife 

resources of the United States or the public health.” THE FNWA gave USDA authority to 

designate plants as noxious weeds by regulation, and the movement of all such weeds in 

interstate or foreign commerce was prohibited except under permit. USDA was also given 

authority to inspect, seize and destroy products, and to quarantine areas, if necessary to 

prevent the spread of such weeds.

Witchweed was the first weed targeted for regulation, and was actually addressed via a 

Federally funded program prior to APHIS’s existence in 1957. Witchweed, and the first 22 

weeds (including hydrilla and a number of parasitic weeds) were first regulated under FNWA in 

1976. A Technical Committee to Evaluate Noxious Weeds was formed in 1979, and the next set 

of weeds was regulated in 1981. Historically, weeds regulated under FNWA authority were 

highly competitive with crops, or damaging to natural areas or aquatic habitats, or waterways.

In 2000, the PPA altered the definition of “noxious weed” by expanding the applicability 

of the definition to include aquatic weeds and weeds in natural areas, and by removing the

limitation on listing weeds that are “new to or widely prevalent” in the United States. 

Originally much of the control/eradication work to address listed and regulated noxious 

weeds was done by APHIS, but now most efforts are funded through Cooperative Agreements 

with state or private stakeholders. Today, the vast majority of program funding is dedicated to 
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addressing a small number of targeted Federal noxious weed priorities, including the following 

examples of listed noxious weeds:

Asian dodder (Cuscuta japonica)

Caulerpa - Med. clone (Caulerpa taxifolia) Eradicated

Cogongrass (Imperata cylindrica)

Common Broomrape (Orobanche minor)

Branched Broomrape (Orobanche ramosa)

Giant Hogweed (Heracleum mantegazzianum)

Giant Salvinia (Salvinia molesta)

Goatsrue (Galega officinalis)

Hydrilla (Hydrilla verticillata)

Onionweed (Asphodelus fistulosus)

Tropical Soda Apple (Solanum viarum) 

Tropical Spiderwort, aka Benghal Dayflower (Comelina benghalensis)

Witchweed (Striga asiatica)

Wormleaf salsola (Salsola vermiculata)

Each of these listed noxious weeds has proven to have significant impacts in areas where they 

have been introduced, and the damage several of them cause is described later in this 

document. 

Kentucky Bluegrass

Kentucky bluegrass is grown throughout the United States; it is commonly known as a 

turf crop that can provide dense green sod that is especially adapted for parks and home lawns. 

It is highly prized and significant investments are made by citizens to maintain a healthy 

Kentucky bluegrass lawn. Kentucky bluegrass is often encountered in pasture and prairie plant 

communities; where it would be considered a forage crop. It can also become established in 

semi-open woodlands and rangelands. Kentucky bluegrass can also volunteer in agricultural 

production systems (e.g. row crops, fruit trees, nurseries). 

Established weed management practices are used throughout the United States to 

maintain the desired balance of plant species within the plant communities in agricultural, 

horticultural and rangeland/prairies systems. Kentucky bluegrass is a preferred pasture grass in 

some areas of the country and considered a less desirable and potentially weedy plant in other 

portions of the country where it can compete with native grassland species; management 

systems for Kentucky bluegrass vary dependent upon the ecosystem under consideration. 

Kentucky bluegrass is effectively managed through use of standard practices that have multiple 
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benefits; implementation of these measures is not solely triggered by the presence of Kentucky 

bluegrass. Management options include the measured use of animals for grazing, mowing, 

mechanical removal and prescribed burns; the latter of which is renowned for many benefits it 

affords to prairie/pasture/rangeland systems that go well beyond benefits derived from 

Kentucky bluegrass management alone. In certain instances, herbicides may be used to control 

Kentucky bluegrass. There are several registered herbicides that are available that provide 

effective control.

In 2009, Kentucky bluegrass yielded sales receipts at $52.4 million nationwide, nearly 

half of which resulted from exports. Export market values in the last five years averaged 

approximately $25 million.

For the purposes of most of our review of the petition, we will refer to Kentucky 

bluegrass, generally, to mean both herbicide tolerant and non-tolerant types. Both are the 

same species, and our analysis shows that the only distinction between the two is glyphosate 

tolerance. This suggests that in the field, GE and non-GE Kentucky bluegrass will behave exactly 

the same, except that the glyphosate tolerant Kentucky bluegrass will survive glyphosate 

treatment, while the non-tolerant Kentucky bluegrass will not. The GE type would be 

theoretically more difficult to control were it not for the fact that alternative management 

practices would continue to be effective for the control of Kentucky bluegrass regardless of its 

ability to tolerate glyphosate treatment. We have concluded, on the basis of our WRA, that the 

risks posed by Kentucky bluegrass regardless of whether it has been genetically engineered for 

glyphosate tolerance are essentially the same. Thus, consistent with the provisions of the PPA 

which provide APHIS authority to regulate noxious weeds, it has been the Agency’s policy to 

regulate at the species level. As such, any decision to regulate GE Kentucky bluegrass as a 

Federal noxious weed would obligate us to do the same for both types of Kentucky bluegrass. 

The minor distinction in risk between the two is reflected in the results of the Weed Risk 

Assessment (described in more detail below); the Impact Potential scores differ by only one 

point, and that difference is again due specifically to glyphosate tolerance.

Considerations for Decisionmaking

In evaluating a request to list a proposed species as a noxious weed, we ask two 

overarching questions:

1. Does the species proposed for listing meet the PPA definition of a noxious weed? 

2. If the answer to question 1 is yes, then should the species be listed as a noxious weed 

and regulated by the Secretary?

Our evaluation of the petition within the framework of these two questions is described in 

detail below.
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Does the species proposed for listing meet the PPA definition of a noxious weed?

In order to be considered for listing, the plant must meet the definition of a noxious 

weed. The term “noxious weed” means any plant or plant product that can directly or 

indirectly injure or cause damage to crops (including nursery stock or plant products), livestock, 

poultry, or other interests of agriculture, irrigation, navigation, the natural resources of the 

United States, the public health, or the environment.

The first consideration in determining if a plant is a noxious weed is identifying what 

direct injury or damage (physical harm) the plant may cause. If direct harm or damage is 

possible, the next consideration is to evaluate any indirect damage the plant may cause to 

interests of agriculture, irrigation, navigation, the natural resources of the United States, the 

public health, or the environment. 

We prepared a weed risk assessment (WRA), entitled “Weed Risk Assessment for nonherbicide resistant and herbicide resistant types of Poa pratensis L.” The purpose of the weed 

risk assessment was to evaluate the weediness of non-herbicide tolerant (non-genetically 

engineered, or non-GE) and herbicide tolerant (GE) types of Kentucky bluegrass, and determine 

whether or not the species (which encompasses both types) is a candidate for listing as a 

Federal noxious weed. While the analysis was based solely on field observations using non-GE 

Kentucky bluegrass (glyphosate susceptible), we consider that the two types will behave in a 

similar manner to other crops that differ solely with respect to GE-glyphosate tolerance. In the 

field, GE and non-GE Kentucky bluegrass are expected to behave exactly the same, except that 

the glyphosate tolerant type will survive glyphosate treatment, while the non-tolerant type will 

not. The WRA does not by itself draw conclusions about whether a species should be 

considered a Federal noxious weed, but provides an analysis to policymakers to inform their 

consideration of regulatory decision making. 

To determine whether or not Kentucky bluegrass is a candidate for listing, we used a 

weed risk assessment tool that was validated using data on 204 plant species with known 

noxious behavior in the United States. This validated weed risk assessment tool predicts weed 

risk potential based on scores for Impact Potential (i.e., harm), and Establishment/Spread 

Potential. The model estimates Impact Potential with 18 scored questions related to the types 

of damage to crops or the environment that a species may cause (e.g., reducing crop yields, 

requiring control, changing community function or structure, adverse effects on human health). 

We assess Establishment/Spread potential using 27 scored questions on species biology and 

history (e.g., invasiveness elsewhere, dispersal mechanisms, likelihood of being a contaminant, 

reproduction). The model was developed to assess basic invasiveness of plants, however, and 

not to distinguish between plant types with different genotypes. 
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The Establishment/Spread Potential scores for the two types of Kentucky bluegrass 

were 23 for the non-GE type, and 24 for the GE type, which are high on the scale of -25 to 32. 

The one point difference, which is not significant, is due entirely to the glyphosate tolerance of 

the GE type. 

For Impact Potential, both types scored 2.5 on a scale of 1 to 5.1. That score exceeds all 

those for non-invasive species in the validation dataset, but is low or moderate when compared 

with scores for High risk species. The most harmful species in the validation dataset (e.g., 

Canada thistle, Cirsium arvense) have Impact Potential scores of 4 or greater. In this case, 

because the model is qualitative, the score for Impact Potential may overestimate the true 

damage this species can cause. For example, although Kentucky bluegrass can act as a weed in 

U.S. agricultural systems, we found very few reports. It is also reported to be a weed of 

production crops in only two other countries, despite a wide distribution throughout Europe 

and Asia. Some recent studies indicate that Kentucky bluegrass can invade U.S. prairie or 

grassland ecosystems, but general weed management programs are typically recommended in 

such situations. Finally, no states regulate Kentucky bluegrass or have it prioritized for control.

Based on those scores, the predictive logistic regression model indicated that both the 

non-GE and GE types have High weed risk potentials. Our uncertainty about these findings was 

small because of the abundance of information about the biology, behavior, and performance 

of non-GE Kentucky bluegrass in the United States. The analysis concludes that Kentucky 

bluegrass species P. pratensis (including GE and non-GE) can be considered for regulation as a 

Federally listed noxious weed. 

Our review of the WRA shows that there is evidence that Kentucky bluegrass has caused 

some problems in grassland or prairie ecosystems, when such areas are not managed properly 

(e.g., Grant et al., 2009). Kentucky bluegrass spreads aggressively (Nature Serve, 2011; Weber, 

2003). It has escaped cultivation into native prairies (Grant et al., 2009). The WRA also found 

that Kentucky bluegrass can act as a weed in U.S. agricultural systems (e.g., Bridges, 1992) and

is reported to be a weed of production crops in two other countries, despite a wide distribution 

through Europe and Asia. It is listed as an arable weed in Japan (Holm et al., 1979; Morita, 

1997), and in Australia, it is an agricultural weed. Given that Kentucky bluegrass shows 

potential to cause damage to crops and natural resources of the United States, we conclude 

that Kentucky bluegrass meets the PPA definition of “noxious weed.”
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Should the species be listed as a noxious weed by the Secretary?

The distinction between a weed and a noxious weed warrants emphasis. “Weeds,” in 

the broadest sense of the word, could include any plant growing where and/or when it is 

unwanted; even plants that are desirable in some settings may be considered weeds in others. 

In a narrower sense, weeds are invasive, often non-native, plants which impact natural and 

managed ecosystems, often with significant negative consequences due to lost yields, changes 

in management practices, altered herbicide use, etc. Only a fraction of these problematic 

weeds are considered to be so invasive, so harmful, and so difficult to control that Federal 

regulatory intervention to prevent their introduction or dissemination is justified, and these are 

the focus of the regulatory controls placed on them by APHIS. The Plant Protection Act 

commits the decision to list a weed as a noxious weed to the discretion of the Secretary. In 

general, federally listed noxious weeds are species that are likely to be aggressively invasive, 

have significant negative impacts, and are extremely difficult to manage or control once 

established.

APHIS currently lists 98 aquatic, terrestrial, or parasitic plant taxa as noxious weeds. The 

species included in the list illustrate the kinds of plants APHIS considers to be sufficiently 

invasive, damaging, and difficult to control to be deemed noxious weeds. Table 1 describes 

some specific examples from the Federal noxious weed list and the kinds of negative impacts 

noxious weeds can have, to illustrate the types of effects APHIS will be looking for when 

evaluating whether plants reviewed under the PPA to have any potential noxious weed traits. 

Table 1.—Examples of impacts caused by federally listed noxious weeds

Impact Description of impact Example species

Lost 

productivity 

of crop fields

Noxious weeds may 

directly compete with 

crop plants for limited 

resources, dramatically 

reducing yields.

Cogongrass (Imperata cylindrica) infests 

over 20 crop species; it releases chemicals 

into the soil that suppress crop growth and 

causes damaging puncture wounds to plant 

roots, bulbs, and tubers. Other examples 

include Benghal dayflower (Commelina

benghalensis), red rice (Oryza spp.), and 

kikuyugrass (Pennisetum clandestinum). 
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Impact Description of impact Example species

Parasitic 

damage to 

crops

Parasitic plants can cause 

significant reductions in 

yield by attaching 

themselves to a host 

plant, removing 

nutrients and ultimately 

killing it.

Federally listed noxious parasitic plants 

include the dodders (Cuscuta spp.)—with 

common names like strangleweed, devil’sguts, hellbine, and witch’s hair— and 

witchweed (Striga spp.), which causes 

devastating losses in corn, sorghum, and 

rice. 

Reduced 

productivity 

of pasture 

Grazing animals may 

avoid noxious weeds and 

consume the more 

favorable pasture 

species, resulting in 

increased noxious weed 

populations at the 

expense of more 

favorable species. 

Noxious weeds may also 

outcompete desirable 

pasture species. 

Serrated tussock (Nassella trichotoma) has 

heavily infested large areas, leaving them 

completely incapable of supporting 

livestock.

Injury to 

humans or 

livestock 

Many noxious weeds are 

toxic, harming humans 

or livestock either when 

consumed or by direct 

contact.

Cape tulip (Homeria spp.) contains a 

cardiac glycoside, which can be fatal to 

livestock. Contact with giant hogweed 

(Heracleum mantegazzianum) causes 

painful skin blisters. Three-cornered jack 

(Emex australis) and devil’s thorn (Emex

spinosa) both bear spiny fruits that can 

cripple or cause injury to livestock or other 

animals.

Unchecked 

overgrowth

Noxious weeds may be 

capable of completely 

dominating the 

landscape and 

preventing the use of 

cultivated or pasture 

lands for agriculture.

Mile-a-minute vines (Mikania cordata and 

M. micrantha) can entirely smother fields 

and forests in a dense, tangled mass of 

vines. A single plant of the aquatic weed 

giant salvinia (Salvinia spp.) can blanket 40 

square miles in 3 months, and produce an 

underwater mat 3 feet thick.
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Impact Description of impact Example species

Physical 

obstructions

Growth rate and habit of 

some noxious weeds 

may physically hamper 

the movement of 

livestock and humans, or 

interfere with navigation 

of waterways. 

Certain mesquites (Prosopis spp.), jointed 

prickly pear (Opuntia aurantiaca), and 

African boxthorn (Lycium ferocissimum) 

form impenetrable thickets filled with 

thorns or needles, blocking the movement 

of grazing animals, injuring them or 

preventing access to food and water.

Disruption of 

water flow

Aquatic noxious weeds 

may disrupt water flow, 

adversely affecting 

irrigation, drainage and 

flood control canals, city 

water intakes, and 

recreational water use. 

Notable examples include hydrilla (Hydrilla

verticillata), giant salvinia (Salvinia spp.), 

and Chinese waterspinach (Ipomoea

aquatica). Dense mats of oxygen weed 

(Lagarosiphon major) can completely shut 

down operation of hydroelectric plants.

Habitat 

alteration

Noxious weeds may 

severely alter water 

quality by changing 

oxygen and nutrient 

content, may 

dramatically lower local 

water tables, or could so 

significantly outcompete 

or overgrow other 

vegetation resulting in a 

complete ecological shift 

of the habitat. 

Infestation of lakes and ponds with hydrilla 

(Hydrilla verticillata) can alter aquatic 

ecosystems so drastically that native plants 

are entirely eliminated, rendering the 

habitat unsuitable for fish and other 

wildlife.

Certainly, some noxious weeds can cause physical harm to the health of humans or 

livestock and other animals. In general, these impacts occur when individuals come into direct 

contact with the noxious plants or plant parts, which may cause physical injury or are toxic or 

otherwise harmful when consumed. Conceivably, noxious weeds growing in crop fields could 

potentially threaten public health, for example, if toxic parts of the noxious weeds are 

harvested and inadvertently enter the food supply. If such toxic or otherwise harmful noxious 

weed parts were found in food and caused the food to be “adulterated” within the meaning of 

the FFDCA, FDA could take regulatory action against the food. 

Our review of the WRA and analysis above shows that Kentucky bluegrass has not 

caused the kinds of impacts that we see from currently listed Federal noxious weeds. The WRA 
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found that although Kentucky bluegrass can act a weed in U.S. agricultural systems, that is only 

reported by Bridges (1992) for a total of three crops—apples, spearmint, and peppermint—out 

of the hundreds of crops grown in the United States. In apples, we have found no evidence of it 

being a significant weed (e.g., listed but with no indication of severity in Rifai et al., 2002 [Nova 

Scotia, Canada]). Another report has volunteer bluegrass as a weed in bluegrass seed plots (Lee, 

1978). Given both the long history of Kentucky bluegrass in the United States and the paucity of 

domestic reports about weedy behavior under a diverse range of weed management strategies, 

it seems highly unlikely that it is a significant weed in managed agricultural systems in the 

United States.

The WRA also found that Kentucky bluegrass is reported to be a weed of production 

crops in only two other countries, despite a wide distribution through Europe and Asia. It is 

listed as an arable weed in Japan (Holm et al., 1979; Morita, 1997), but is not regulated or 

heavily controlled (NIES, 2011). In Australia, it is an agricultural weed, but was not ranked as 

either a noxious weed, or a serious, high impact weed (Randall, 2007).

Most of the evidence gathered through the WRA process for invasiveness by Kentucky 

bluegrass comes from grassland or prairie ecosystems. When it invades native prairies, the 

recommended management is typically to apply general, adaptive (i.e., location specific) 

programs to control multiple species, not just Kentucky bluegrass (e.g., Grant et al., 2009; 

Hendrickson and Lund, 2010). Preferred methods of control are grazing and controlled burns 

(FEIS, 2009). Fire is usually a successful method of control for Kentucky bluegrass in these 

systems (Sather, 1996). When herbicides are used in such situations, invasive Kentucky 

bluegrass populations can be reduced to low levels in one or two seasons (Waller and Schmidt, 

1983). The tolerance of Kentucky bluegrass to glyphosate would not affect the ability of land 

managers and farmers to manage it.

The WRA found that Kentucky bluegrass has demonstrated value in some natural areas, 

however. For example, it can be an important part of the diet of wildlife (e.g., elk, bighorn 

sheep) (FEIS, 2009), and Kentucky bluegrass is one of the most important forage species for 

cattle and sheep summering in mountain meadows in eastern Oregon (McInnis and Vavra, 

1986). The WRA also notes that Kentucky bluegrass is a recommended pasture grass in some 

eastern and western states (e.g., Tregoning, N/D; Wiedmeier et al., 2005), and is widely grown 

as a turfgrass species in all 50 United States. 

Given the very limited reports of domestic damage caused by Kentucky bluegrass 

despite substantial plantings all over the country, together with the apparent lack of interest at 

the state or local government level in managing it as a weed that poses unique or challenging 

control strategies, Kentucky bluegrass does not appear to warrant listing and regulation as a 

Federal noxious weed.
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Funding for federal regulatory response for Kentucky bluegrass is unlikely to be available 

at a time when our noxious weed program is facing funding limitations, and the required 

response would be beyond the combined federal and state regulatory capacity.

Furthermore, the PPA does not provide authority to hold, seize, quarantine, treat, apply 

other remedial measures to, destroy, or otherwise dispose of any noxious weed being imported 

or moving in interstate commerce unless the noxious weed is “new to or not known to be 

widely prevalent” in the United States. Kentucky bluegrass is neither. Therefore, the 

widespread prevalence of Kentucky bluegrass regardless of glyphosate tolerance would 

preclude any sort of eradication effort or other effective regulatory response. 

APHIS has little authority to take regulatory actions related to preventing the evolution 

of herbicide-tolerant weeds. While the PPA gives APHIS the authority to regulate noxious 

weeds, to date APHIS has never regulated a weed as “noxious” due to its resistance to an 

herbicide alone, nor has it ever taken action to prevent the evolution of noxious weeds.

Herbicide resistant weeds are not an issue exclusively associated with the use of 

herbicides on genetically engineered herbicide tolerant crops. Many weed species have 

evolved resistance to a wide variety of herbicides, long before the advent of GE crops, resulting 

from the common use of herbicides in agriculture for decades.

We have no evidence, whether in the WRA or otherwise, that Kentucky bluegrass poses 

a threat to irrigation, navigation, or public health. There are no states that have regulations or 

have published weed risk analyses for Kentucky bluegrass, which suggests that control of 

Kentucky bluegrass is not a priority for States. 

Conclusion

For all these reasons, APHIS has determined that Kentucky bluegrass Poa pratensis L.,

whether GE or not, should not be listed as a noxious weed in 7 CFR Part 360 pursuant to the 

PPA and the regulations.

Literature Cited

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Society of America, Champaign, Illinois, USA.

FEIS. 2009. USDA Forest Service-Fire effects information center. USDA Forest Service. 

http://www.fs.fed.us/database/feis/. (Archived at PERAL).

Grant, T. A., B. Flanders-Wanner, T. L. Shaffer, R. K. Murphy, and G. A. Knutsen. 2009. An 

Emerging Crisis across Northern Prairie Refuges: Prevalence of Invasive Plants and a Plan 

for Adaptive Management. Ecological Restoration 27(1):58-65.

Hendrickson, J. R., and C. Lund. 2010. Plant Community and Target Species Affect Responses to 

Restoration Strategies. Rangeland Ecology & Management 63:435-442.

Holm, L. G., J. V. Pancho, J. P. Herberger, and D. L. Plucknett. 1979. A Geographical Atlas of 

World Weeds. Krieger Publishing Company, Malabar, Florida, U.S.A. 391 pp.
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Lee, W. O. 1978. Volunteer Kentucky bluegrass (Poa pratensis) control in Kentucky bluegrass 

seed fields. Weed Science 26(6):675-678.

McInnis, M.L., and M. Vavra. 1986. Summer diets of domestic sheep grazing mountain 

meadows in northeastern Oregon. Northwest Science. 60(4): 265-270.

Morita, H. 1997. Handbook of Arable Weeds in Japan. Niimura Printing Co., Ltd., Tokyo. 128 pp.

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System (NAPPFAST). 

http://www.nappfast.org/databases/NAPPFAST%20Databases.htm. (Archived at 

PERAL).

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Biology and Ecosystem Studies, National Institute for Environmental Studies, Ibaraki, 

Japan. http://www.nies.go.jp/biodiversity/invasive/DB/detail/80770e.html (Archived at 

PERAL)

Randall, J. M. 2007. The introduced flora of Australia and its weed status. CRC for Australian 

Weed Management, Department of Agriculture and Food, Western Australia, Australia.

Rifai, M.N., T. Astatkie, M. Lacko-Bartosova, and J. Gadus. 2002. Effect of two different thermal 

units and three types of mulch on weeds in apple orchards. Journal of Environmental 

Engineering and Science. 1: 331–338.

Sather, N. 1996. Element Stewardship Abstract for Poa pratensis, Poa compressa. The Nature 

Conservancy, Minneapolis, MN. 21 pp.

Tregoning, D. No date.Pasture Renovation and Seeding. Montgomery County Cooperative 

Extension, Maryland. 

http://www.equinestudies.umd.edu/documents/UMSeminar/Tregoning.pdf (Archived 

at PERAL)

Waller, S. S., D.K. Schmidt. 1983. Improvement of eastern Nebraska tallgrass range using 

atrazine or glyphosate. Journal of Range Management. 36(1): 87-90. 

Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental 

Weeds. CABI Publishing, Wallingford, UK. 548 pp.

Wiedmeier, R.D., D.R. ZoBell, A.C. Young, and P.R. Schmidt. 2005. Yearly Forage Production of 

Irrigated Pastures Grazed by Cow-Calf Pairs as Affected by the Timing of Sprinkler 

Irrigation Application. Department of Animal, Dairy and Veterinary Sciences, Utah State 

University, Logan.