Developing a Detection Method for New Invaders at the Landscape Scale

By Lisa C. Jones and Timothy Prather, University of Idaho. Presented at the Western Society of Weed Science Annual Meeting, 2018.

Abstract: The ability to predict plant invasions and detect them early in the process are important considerations for invasive plant management. While agencies and landowners typically take the approach of on-the-ground searches and some may utilize habitat suitability models, these tools may not facilitate detection of incipient infestations when the species is unknown. We set out to develop a method to identify where to look for a new invader to assist managers in focusing search efforts to areas more prone to invasion. We used habitat suitability models (also referred to as species-specific susceptibility models) of seven plant species to investigate whether creating weed “hotspots” of overlapping models was an effective tool to infer areas more invaded within the boundaries of a 4,200-ha ranch in southern Idaho. We tested this by sampling vegetation cover by species, in five, 0.125 m2 quadrats placed along each of 24 transects located in areas modeled to be suitable habitat for either zero, two, four, or six weed species located in the northeast section of the ranch. Since it is well-documented that roads and trails provide corridors for dispersal, we located transects either near (within 60 m) or far (more than 60 m) from unimproved roads. We hypothesized that non-native species richness and/or cover would be higher in hotspots where a greater number of suitability models overlapped closer to roads. Of the 46 unique species in our quadrats, five species (11%) were non-native, of which Japanese brome (Bromus japonicus) and downy brome (Bromus tectorum) were the most abundant. Among non-native species, there was no significant difference in richness or foliar cover between hotspots or proximity to roads. Among native species, richness and foliar cover were not significantly different between hotspots, but they were curiously greater in transects closer to roads. To further aid the development of a detection method for new invaders, we examined indicator species that are positively or negatively associated with Japanese and downy brome. Notably, when downy brome cover was high, two perennial native forbs were in greater abundance, and when downy brome was not present, Sandberg’s bluegrass (Poa secunda) cover was high. There were no positive indicator species for Japanese brome, though there were 11 native species negatively associated with it. Overall, our initial foray to develop a detection method using existing weed habitat suitability models was not successful in identifying areas at greater risk of invasion as evidenced by current diversity and cover of non-native species. However, we recognize the limits of our small sample size and narrow extent of the area surveyed (15% of the ranch). Identifying sites at high risk to invasion when the life history traits and environmental niche of the invader is unknown is a complex challenge, but one that has the potential to help land managers prioritize areas for invasive plant monitoring. Future tests will investigate if there are specific modeled weed species combinations that are suggestive of areas generally susceptible to invasion; for example, more non-native species were along transects located where leafy spurge (Euphorbia esula) habitat was predicted. Further, indicator species may be used to reveal which models are better candidates for estimating invasibility.

Timing Aminopyralid to Prevent Seed Production, Control Medusahead (Taeniatherum caput-medusae), and Increase Forage Grasses

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By Matthew J. Rinella, Josh S. Davy, Guy B. Kyser, Fadzayi E. Mashiri, Susan E. Bellows, Jeremy J. James and Vanelle F. Peterson

Presented at Western Society of Weed Science Annual Meeting, 2018.

Abstract: Exotic annual grasses such as medusahead [Taeniatherum caput-medusae (L.) Nevski] and downy brome (Bromus tectorum L.) dominate millions of hectares of grasslands in the western United States. Applying picloram, aminopyralid, and other growth regulator herbicides at late growth stages reduces seed production of most exotic annual grasses. In this study, we applied aminopyralid to T. caput-medusae to determine how reducing seed production in the current growing season influenced cover in the subsequent growing season. At eight annual grassland sites, we applied aminopyralid at 55, 123, and 245 [ 1 ] g ae ha −1 spring just before T. Caput-medusae heading. The two higher rates were also applied pre-emergence (PRE) in fall to allow comparisons with this previously tested timing. When applied in spring during the roughly 10-d period between the flag leaf and inflorescence first becoming visible, just 55 g ae ha −1 of aminopyralid greatly limited seed production and subsequently reduced T. caput-medusae cover to nearly zero. Fall aminopyralid applications were less effective against T. caput-medusae, even at a rate of 245 g ae ha −1. The growing season of application, fall treatments, but not spring treatments, sometimes reduced cover of desirable winter annual forage grasses. The growing season after application, both spring and fall treatments tended to increase forage grasses, though spring treatments generally caused larger increases. Compared with other herbicide treatment options, pre-heading aminopyralid treatments are a relatively inexpensive, effective approach for controlling T. caput-medusae and increasing forage production.


[ 1 ] Aminopyralid rates of 55, 123 and 245 grams ae/ha are equivalent to Milestone® specialty herbicide at 3, 7 and 14 fluid ounces per acre respectively.

Canada Thistle Affects Herbage Production in the Northern Great Plains

Canada Thistle (Cirsium arvense) Affects Herbage Production in the Northern Great Plains (2017). Travis R.Carter and Rodney G.Lym. Invasive Plant Science and Management.  

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Abstract: Canada thistle can cause greater than 50% yield loss in small grain crops, but little is known about production losses when the weed invades pasture and wildlands. Change in grass, forb, and woody species production from Canada thistle infestations was evaluated in two separate studies in North Dakota. The first measured change in production following aminopyralid applied at 120 g ha−1 to control Canada thistle at two prairie sites. In general, grass, broadleaf, woody, and total plant yields were similar between treated and untreated prairie, regardless of the near-complete control of Canada thistle following aminopyralid application. Grass yield increased by 365 kg ha−1 the year after treatment at one location, with no change in forb or woody species production. Plant production was also estimated at 20 ungrazed wildland preserves located within two Major Land Resource Areas (MLRAs). Similar to the prairie sites, minimal differences in production between Canada thistle–infested and noninfested sites were observed. The only exception was an increase in grass production of 425 kg ha−1 at one of the MLRAs, with no change in broadleaf or woody species production between the Canada thistle–infested and non-infested sites. In contrast to cropland, pasture and wildland production of other species was not consistently reduced by Canada thistle.

[CLICK HERE TO SEE FULL LIST OF REFERENCES]


economic threshold for control of canada thistle with aminopyralid

 FIGURE: Economic threshold for control of Canada thistle with aminopyralid applied at 120 g ha-1 based on forage response at Fargo and the Rolling Soft Shale Plains in North Dakota in 2015 and 2016.  Maximum stem density at the study sites was 27 stems m-2 in Fargo and 35 stems m-2 in the Rolling Soft Shale Plains. Gray segments were an extrapolation beyond observed Canada thistle densities to estimate cost-effective stem density required for treatment based on forage response. The standard error of the mean was 10.1 and 8.3 at the Fargo and Rolling Soft Shell Plains locations, respectively (Rod Lym, personal communication 2018).

FIGURE: Economic threshold for control of Canada thistle with aminopyralid applied at 120 g ha-1 based on forage response at Fargo and the Rolling Soft Shale Plains in North Dakota in 2015 and 2016.  Maximum stem density at the study sites was 27 stems m-2 in Fargo and 35 stems m-2 in the Rolling Soft Shale Plains. Gray segments were an extrapolation beyond observed Canada thistle densities to estimate cost-effective stem density required for treatment based on forage response. The standard error of the mean was 10.1 and 8.3 at the Fargo and Rolling Soft Shell Plains locations, respectively (Rod Lym, personal communication 2018).


For information on the Impact of Canada Thistle Cover on Plant Community Structure in Early Stage Prairie Restoration go to bit.ly/CanadaThistleImpact

Constructing Standard Invasion Curves from Herbarium Data—Toward Increased Predictability of Plant Invasions

by Pedro M. Antunes and Brandon Schamp. Invasive Plant Science and Management, 10(4):293-303. 2017.

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Is it possible to predict which nonnative plant species will become invasive weeds and when? Authors explore challenges related to developing invasion curves for plants using herbarium data.  The goal is to better position herbaria and researchers to assist natural resource managers in prioritizing needs, supporting management decisions and developing prevention and monitoring programs.  

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Secondary Invasion and Reinvasion after Russian-Olive Removal and Revegetation

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Erin K. Espeland, Jennifer M. Muscha, Joseph Scianna, Robert Kilian, Natalie M. West, and Mark K. Petersen. Invasive Plant Science and Management October-December 2017 Vol. 10, No0. 4: 340-349.

Cut-stump application of triclopyr provided 96% control of Russian olive the year following treatment.  Seeded native species did not have trouble establishing once adequate spring moisture occurred in the second growing season after Russian-olive removal, indicating that removal did not present substantial obstacles to successful revegetation. Follow-up control of Russian-olive is critical after initial treatment. [ READ FULL ABSTRACT. ]

Forest Roads Facilitate the Spread of Invasive Plants

 Photo by Chuck Bargeron, University of Georgia, Bugwood.org

Photo by Chuck Bargeron, University of Georgia, Bugwood.org

David A. Mortensen and others. Invasive Plant Science and Management 2(3):191-199.

This large-scale survey highlights the importance of roads in predicting the presence of invasive plants, also revealing that one invasive plant, Japanese stiltgrass (Microstegium vimineum), has spread rapidly since its introduction. READ FULL ABSTRACT HERE 

Plains Cottonwood’s Last Stand: Can It Survive Invasion of Russian Olive onto the Milk River, Montana Floodplain?

 www.mt.nrcs.usda.gov

www.mt.nrcs.usda.gov

Pearce and Smith. 2001. Environmental Management Vol. 28, No. 5, pp. 623–637

The eventual replacement of native plains cottonwood (Populus deltoides) forests by Russian olive (Elaeagnus angustifolia) is a serious threat to biodiversity on floodplains in western North America. Low palatability  of Russian olive saplings and trees, easily dispersed seed, and three-year seed viability give Russian olive a competitive advantage over native woody riparian plants. Read entire article here.

Propagule pressure and environmental conditions interact to determine establishment success of an invasive plant species, glossy buckthorn (Frangula alnus), across five different wetland habitat types

Berg, J.A., Meyer, G.A. & Young, E.B. Biol Invasions (2016) 18: 1363. Brief Abstract.

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Many invasive plant species are able to establish within a wide range of community types. This study aimed to investigate interactions between propagule pressure and environmental resistance to seedling recruitment of the invasive shrub, glossy buckthorn (Frangula alnus Mill.), over a range of wetland habitat types. Results showed that drier habitats supported more woody species and provided more raised hummock surfaces essential for successful buckthorn recruitment and establishment; and provides empirical evidence that environmental resistance can be overcome by higher propagule pressure.

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