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National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 

Garlic Mustard (Alliaria petiolata) Early Detection 

Monitoring at Homestead National Monument of America 

Natural Resource Report NPS/HTLN/NRDS—2010/259 
ON THE COVER 

Garlic mustard plant found at Homestead National Monument of America. 

Photograph by: Jesse Bolli, Resource Management Specialist, Homestead National Monument of America. 
i 

Garlic Mustard (Alliaria petiolata) Early Detection 

Monitoring at Homestead National Monument of 

America 

Natural Resource Report NPS/HTLN/NRDS—2010/259 

Mary F. Short, Craig C. Young, and Chad S. Gross 

National Park Service, Heartland I&M Network 

Wilson’s Creek National Battlefield, 6424 West Farm Road 182, Republic, MO 65738 

Jesse M. Bolli 

National Park Service 

Homestead National Monument of America, 8523 W. State Hwy 4, Beatrice, NE 68310 

October 2010 

U.S. Department of the Interior 

National Park Service 

Natural Resource Program Center

Fort Collins, Colorado 
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This report is available from the Heartland Inventory and Monitoring Network 

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Please cite this publication as: 

Short, M. F., C. C. Young, Bolli, J. M., and C. S. Gross. 2010. Garlic mustard early detection 

monitoring at Homestead National Monument of America. Natural Resource Report 

NPS/HTLN/NRDS—2010/259. National Park Service, Fort Collins, Colorado.

NPS 368/105868, October 2010 
iii 

Contents 

Page 

Executive Summary ....................................................................................................................... iv

Introduction ..................................................................................................................................... 1

Methods........................................................................................................................................... 1

Results and Discussion ................................................................................................................... 1

Literature Cited ............................................................................................................................... 3
iv 

Executive Summary 

In the spring of 2010 a search for garlic mustard (Alliaria petiolata), a non-native invasive plant 

species, was conducted at Homestead National Monument of America. Garlic mustard occurs 

throughout eastern and south-central Nebraska, including Gage County where the park is located. 

On April 26, 2010, prior to our search, a small amount of garlic mustard was found at the 

monument and hand-pulled. Our comprehensive search of all woodland habitat in the park a few 

days later found no garlic mustard. We hope that early detection and removal efforts have 

eradicated garlic mustard from the park.
1 

Introduction 

A non-native biennial, garlic mustard (Alliaria petiolata) invades woodlands throughout the 

Eastern and Midwest regions of the United States (Anderson et al. 1996). Garlic mustard is a 

shade-tolerant species and prefers shaded habitat, including both disturbed and undisturbed 

woodland (Anderson et al. 1996, Kaul 2006). Several mechanisms have contributed to the 

success of garlic mustard invasion in North American forests (Rodgers et al. 2008). Garlic 

mustard contains secondary compounds that reduce the plant’s palatability to herbivores, thereby 

allowing garlic mustard a competitive advantage over other understory vegetation (Rodgers et al. 

2008). Furthermore, garlic mustard produces allelopathic compounds in the soil, inhibiting 

germination of other plant species and also affecting soil biota (Prati and Bossdorf 2004, 

Rodgers et al. 2008, Burls and McClaugherty 2008). Garlic mustard’s high seed production and 

rapid growth in the second growing season allow garlic mustard to successfully outcompete 

other vegetation (Anderson et al 1996, Rodgers et al. 2008). The impacts of garlic mustard on a 

habitat can include alterations to soil microbial communities, a decrease in native flora 

abundance and loss of biological diversity (Anderson et al. 1996, Rodgers et al. 2008). 

Since the first recorded occurrence of garlic mustard in Nebraska in 1975, the species has been 

found in at least 18 counties in the state, including Gage County, the location of Homestead 

National Monument of America (Kaul 2006). Recent increases in the occurrence of garlic 

mustard in eastern Nebraska demonstrate the importance of monitoring for this species at the 

monument (Kaul 2006). 

On April 26, 2010, Jesse Bolli identified a patch of garlic mustard at Homestead National 

Monument of America. The location of the patch was approximately 0683813 meters east and 

4461895 meters north (UTM, Zone 14, NAD83). The patch was approximately 2m x 3m in size 

and consisted of approximately 200 plants. Kent Pfeiffer of Nebraska Game and Parks and 

Karola Mlekush of the Heartland Inventory and Monitoring Network confirmed the 

identification. Jesse Bolli and Jake Warner then removed the plants by hand, collecting a 

volume of approximately 30 gallons. 

Methods 

After detection and removal of the plants, on April 28 and 29, Jesse Bolli Chad Gross, and Craig 

Young searched all wooded areas within Homestead National Monument of America for garlic 

mustard (Figure 1). Second-year plants would have been flowering during the search. Observers 

walked parallel transects, approximately 8 to 10 m apart, across all woodland habitat. While 

individual plants may have been overlooked, we believe that our search would have detected 

patches comparable to the one initially found on the park. Due to a GPS error in the field, we 

were unable to record our exact search paths as intended. 
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Results and Discussion 

Our thorough search of woodland habitat at Homestead National Monument of America found 

no garlic mustard on the park. We hope that the early detection and removal of this invasive 

plant eradicated garlic mustard within the park borders. In this case, early detection was a 

fortuitous finding while Jesse Bolli was conducting control of invasive tree species. Because 

prevention and early detection are principal strategies for successful invasive exotic plant 

management, monument staff should continue to work with the Heartland I&M program and 

Exotic Plant Management Team to monitor for future garlic mustard colonization. Because 

invasive exotic plants quite often undergo a lag period between introduction and subsequent 

colonization, managers can take advantage of early detection monitoring to identify invasive 

exotic species and eradicate these plants before populations become well-established. While 

there is a need for long-term suppression programs to address very high-impact species, 

eradication efforts are most successful for infestations less than one hectare in size (Rejmanek 

and Pitcairn 2002). Costs, or impacts, to ecosystem components and processes resulting from 

invasion also increase dramatically over time, making ecosystem restoration improbable in the 

later stages of invasion. Further, in their detailed review of the nonnative species problem in the 

United States, the U.S. Congress, Office of Technology Assessment (1993) stated that the 

environmental and economic benefits of supporting prevention and early detection initiatives 

significantly outweigh any incurred costs, with the median benefit-to-cost ratio being 17:1 in 

favor of being proactive. (Paragraph uses text directly from Welch 2007) 
2 

Figure 1. Search area for garlic mustard (Alliaria petiolata) at Homestead National Monument of 

America.
3 

Literature Cited 

Anderson, R.C., S.S. Dhillioni, and T. M. Kelley. 1996. Aspects of the Ecology of an Invasive 

Plant, Garlic Mustard (Alliaria petiolata), in Central Illinois. Restoration Ecology 4(2): 181-

191. 

Burls, K. and C. McClaugherty. 2008. Landscape Position Influences the Distribution of Garlic 

Mustard, an Invasive Species. Northeastern Naturalist 15(4): 541-556. 

Kaul, R.B., D. Sutherland, and S. Rolfsmeier. 2006. The Flora of Nebraska. School of Natural 

Resources, University of Nebraska-Lincoln, Lincoln, Nebraska. 

Office of Technology Assessment. 1993. Harmful non-indigenous species in the United States. 

OTA-F-565. U.S. Congress, Government Printing Office, Washington, D.C., USA. 

Prati, D. and O. Bossdorf. 2004. Allelopathic Inhibition of Germination by Alliaria petiolata

(Brassicaceae). American Journal of Botany 91(2):285-288. 

Rejmanek, M., and M. J. Pitcairn. 2002. When is eradication of exotic pest plants a realistic 

goal? Pages 249-253 in C. R. Veitch and M. N. Clout, editors. Turning the Tide: the 

Eradication of Invasive Species. IUCN SSC Invasive Species Specialist Group. IUCN, 

Gland, Switzerland and Cambridge, UK. 

Rodgers, V.L. K.A. Stinson, and A.C. Finzi. 2008. Ready or Not, Garlic Mustard is Moving In: 

Alliaria petiolata as a Member of North American Forests. Bioscience 58(5): 426-436. 

Welch, B.A. 2007. Chapter 1. Introduction. Pages 1-11 in B.A. Welch and P.H. Geissler, editors. 

Early Detection of Invasive Species Handbook, United States Geological Survey, 

unpublished darft. 
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NPS 368/105868, October 2010 
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