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  • Using Hot Foam to Control an Invasive Annual, Bromus tectorum (cheatgrass), before Seeding:Initial Observations
  • Steven O. Link (bio), Lindsay A. Chiono (bio), and Mason K. Murphy (bio)

Bromus tectorum (cheatgrass) is an invasive annual present in much of the western United States (Monaco 2011). The species results in increased fire frequency (Whisenant 1990) and reduced native-plant diversity (Daubenmire 1970) and threatens the habitat for sensitive species such as Centrocercus urophasianus (greater sage-grouse) (Connelly et al. 2000). This has engendered numerous restoration efforts using herbicides to control B. tectorum before seeding native species (Monaco et al. 2017). Unfortunately, using herbicides leads to resistance and environmental effects, such as interference with salmon olfaction when exposed to glyphosate (Tierney et al. 2006), which has been detected in precipitation and rivers (Battaglin et al. 2014). Hot foam is a nontoxic method (Wei et al. 2010) that would reduce risks to [End Page 157]


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Figure 1.

Applying hot foam to a typical study plot on 5 April 2021 using a Foamstream L12 unit (www.weeding-tech.com) in the bed of an all-terrain vehicle (Gabe Hughes, Turf Star Western). Photo credit: Steven Link

culturally important salmon (Quaempts et al. 2018) and is considered here.

We tested hot foam on a B. tectorum infestation to determine initial efficacy. We compared hot foam versus controls on the percent cover and density of B. tectorum. We consider options hot foam presents for B. tectorum control compared with glyphosate.

Testing occurred on the Confederated Tribes of the Umatilla Indian Reservation's Wanaket Wildlife Area near Umatilla, Oregon (45°5426.5608N 119°1255.0728W). The soil is a Starbuck-shallow loam (Soil Survey Staff 2022). The habitat is shrub-steppe, with an average annual precipitation of 207 mm (PRISM 2023). Winter precipitation before treatment was 56 mm, 74.7% of normal; a dry spring (7.9 mm, 13.5% of normal) and summer (5.3 mm, 23.9% of normal) followed the April 2021 hot foam treatment. Precipitation (PRISM 2023) in the fall of 2021 was 66 mm, 129% of normal, followed by a dry winter (55 mm, 73.4% of normal) and wet spring (98 mm, 168% of normal). Plant species in the old rangeland study area are primarily invasive aliens, with small amounts of the native species Amsinckia lycopsoides (tarweed fiddleneck) and Poa secunda (Sandberg bluegrass).

We randomly assigned six hot foam treatments and six controls to 1.2 m × 2.4 m plots. Hot foam (Foamstream, L12, Weeding Technologies Ltd, London) application occurred on 5 April 2021 using a triangular spray head (Figure 1). The solution is water, vegetable oil, polysaccharides from fermented glucose, and glutamic acid mixed at lethal temperatures of 57 to 95°C and applied for an average of 43 seconds/m2.

We made B. tectorum cover observations before (1 April 2021), after (14 April 2021), and one year after (20 April 2022) treatment. We determined B. tectorum density in 2022. We visually estimated cover (Daubenmire 1959) in each 1.2 m × 2.4 m plot and assigned it the mid-point of each cover range (0, 0–5, 5–25, 25–50, 50–75, 75–95, and 95–100%) after Rebele and Lehmann (2002). To determine density, we counted individual plants in a single, randomly placed 1.15 dm2 frame in each plot. [End Page 158]

Data were analyzed using JMP software (JMP v. 16.2.0. SAS Institute, Cary, NC), with α = 0.05. We transformed percentage data (Steele and Torrie 1960) as follows:

We compared transformed percent cover and B. tectorum density in treated and control plots with Student's t-test. The coefficient of variation (cv = σ/µ), where σ is the standard deviation and µ the mean, was used to examine transformed % cover and density variation. We present results with untransformed data. Error terms are one standard error of the mean (sem).

Variation in B. tectorum cover in 2022 was greater in hot foam plots (cv = 0.36) than in controls (cv = 0.11). Plots in the hot foam treatment had a wider range of B. tectorum cover (15 to 62.5%) than in controls (62.5...

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