Yellow Starthistle Information
Mech control
-hand
-tillage
-mowing
Cultural control
-grazing
-burning
-re-vegetation
Biocontrol
-insects
-biocontrol table
-plant pathogens
Chem control
- risks
--spray
--water
--toxicology
--herbicide
resist
--effects
-herbicides
--preemergence
--postemergence
--late season
--pre- & post-
--imazapic
--clopyralid
--picloram
Management
Cultural control (continued)
Re-vegetation
Before the introduction of annual grasses, perennial bunchgrasses were the primary natives species in rangelands west of the Rocky Mountains. This included Festuca idahoensis, Poa secunda, Festuca kingii, Pseudoroegneria spicata, Leymus cinereus, Elymus elymoides, Achnatherum hymenoides, Hesperostipa comata, and Achnatherum occidentalis. These perennial grass species do not have high seedling vigor nor do they readily recover from overgrazing (Callihan and Evans 1991). With the introduction of exotic annual grasses and livestock, native perennial grass plants were overgrazed and quickly replaced by introduced winter annual grasses (Young and Longland 1996).
During the past half-century, many noxious broadleaf species have expanded their range in the western United States. Although this can be associated with soil disturbance by human activities, it is also due to selection by livestock overgrazing the annual grasses. Spiny broadleaf species, including yellow starthistle tend to be avoided by livestock. This can favor a rapid shift in the dominant species within these communities (Callihan and Evans 1991). In many cases, these broadleaf species produce an extensive taproot system that can extract more moisture from deep within the soil profile. Thus, they remain green longer into the dry season than do the annual grasses. In addition, these invasive broadleaf species typically produce a large number of seeds (Roché et al. 1994).
In a re-vegetation program designed to suppress noxious weeds, a major limitation is choosing a species, or combination of species, that is more vigorous than the invasive weed. Only a limited number of species have proven to be aggressive enough to displace invasive species, and the proper species choice varies depending on the location and objective. Perennial bunchgrasses are among the most common species used for re-vegetating western grasslands, but broadleaf species such as legumes can also be used in re-vegetation programs to suppress rangeland weeds. In addition to using a competitive species, seeded species also need to be adapted to the soil conditions, elevation, climate, and precipitation level of the site (Jacobs et al. 1999). In the absence of adequate surface soil moisture during the critical spring growing season, re-vegetation programs are likely to fail (Roché et al. 1997). The method of re-vegetation can also determine the level of success. Re-vegetation can be accomplished by broadcast seeding or interseeding forage grasses and/or legumes into existing communities or by drill seeding into plowed, disked, herbicide-treated, or no-till rangeland (Jacobs et al. 1999). Drill seeding programs are considerably more successful than those utilizing broadcast seeding techniques.
Choice of species that best fit the intended use of the site is also important. For example, if livestock grazing is the primary objective of a re-vegetation program, a perennial grass with high forage production may be the appropriate choice (Jacobs et al. 1999). Though perennial grasses have been shown to be most successful in competing with rangeland weeds, using a combination of species with various growth forms and ecological traits may be best, although quite expensive. In other regions of the country, seed mixtures of grasses with legumes improved the rate of microbial and soil structure recovery compared to grasses alone (Jacobs et al. 1999). Using seed mixtures, however, may limit the options for noxious weed control (e.g., using selective herbicides). Thus, a re-vegetation program may require initial seedling with perennial grasses during the weed management phase followed by subsequent re-seeding with broadleaf species. Under this condition, re-vegetation programs may require several years to successfully accomplish.
Re-vegetation programs for yellow starthistle control generally rely on re-seeding with native species or perennial grasses (Callihan et al. 1986, Johnson 1988, Larson and McInnis 1989a, Lass and Callihan 1995a, Northam and Callihan 1988a, 1988b, 1988c, 1990a, 1990b, Prather et al. 1988, Prather and Callihan 1989a, 1989b, 1990, 1991). Consequently, these programs are not only trying to eliminate starthistle, but also the invasive annual grasses that have created a susceptible ecosystem for starthistle invasion. Re-vegetation with desirable and competitive plant species can be the best long-term sustainable method of suppressing weed invasions, establishment, or dominance, while providing high forage production. In western states, other than California, competitive grasses used in re-vegetation programs for yellow starthistle management include crested wheatgrass (Agropyron desertorum), intermediate wheatgrass (Elytrigia intermedia [=Agropyron intermedium], = Thinopyrum intermedium), thickspike wheatgrass (Agropyron dasystachyum), big bluegrass (Poa ampla), Bozoisky Russian wildrye (Psathyrostachys juncea), sheep fescue (Festuca ovina), tall oatgrass (Arrhenatherum elatius), or orchardgrass (Dactylis glomerata) (Borman et al. 1991, Ferrell et al. 1993, Prather and Callihan 1991, Sheley et al. 1999b). These species provide good livestock forage and a sustainable option for rangeland maintenance.
Because of California's Mediterranean climate, re-vegetation programs for control of yellow starthistle are more difficult that those in other western states where summer rainfall is critical to the establishment and survival of native perennial grasses. In the most desirable cases, competitive, endemic, native species should be re-established. This may not always be possible depending on the objective of the land use and the location of the site. In many cases non-native perennial grasses or legumes with high forage quality and quantity are used in re-vegetation programs.
For example, in a study underway near Yreka (Siskiyou County, California) Enloe et al. (1999a, 1999b, 2000) have combined herbicides, biological control, and competitive perennial grass reseeding, using pubescent wheatgrass ('Luna' Thinopyrum intermedium). To establish the perennial grass they employed a late winter glyphosate treatment for annual grass control in the first year and one to three consecutive years' treatment with clopyralid for starthistle control. In the first year, pubescent wheatgrass was spring drill seeded following the herbicide treatments. The goal of this re-vegetation project is to develop sustainable high quality range conditions, improve wildlife habitat, and provide long-term starthistle control without the need for continued herbicide treatments.
Their results showed a first year only treatment with clopyralid and glyphosate was sufficient to allow wheatgrass establishment. In this case, the wheatgrass provided some level of starthistle control in subsequent years, but was not as effective as two or three years of clopyralid treatment with wheatgrass (Enloe et al. 2000). Plots treated with clopyralid and not seeded with pubescent wheatgrass were dominated by introduced annual species, particularly grasses (e.g. downy brome). They also showed that yellow starthistle infestations could deplete soil moisture to a greater degree than rangeland dominated by introduced annual grasses or pubescent wheatgrass. Wheatgrass was able to utilize soil moisture at shallow and intermediate soil depths, whereas starthistle depleted soil moisture at the shallow and deeper soil levels. Heavy infestations of yellow starthistle led to inadequate deep soil moisture recharge after the rainy season. The investigators concluded that on severely degraded rangeland an integrated combination of clopyralid treatment and wheatgrass seeding can suppress yellow starthistle seed production and provides a more effective long-term solution than applying clopyralid alone.
In Oregon, subterranean clover (Trifolium subterraneum) was used for re-seeding programs in foothill ranges (Sheley et al. 1993). This species was effective in annual grass dominated rangelands because of its rapid germination and establishment. However, results were inconsistent in yellow starthistle dominated grasslands, as starthistle has a similar pattern of initial growth.
In California studies, Thomsen et al. (1996a, 1997) and Thomas (1996, 1997) tested several legume (Fabaceae) species for their competitive effect on yellow starthistle. Thomsen et al. (1996a, 1997) found subterranean clover varieties to be the best. In addition to providing some competitiveness against yellow starthistle when combined with grazing and mowing, they were also palatable, self-seeding, and produced flowers and seeds below the bite of grazing animals. Used as a sole control option, however, subterranean clovers did not provide adequate seasonal control of starthistle. Thomas (1996, 1997) used a combination of subterranean clover and/or crimson clover (Trifolium incarnatum) as a cover crop in starthistle infested pasture. In a completely infested field, he reported an 80 to 90% reduction in yellow starthistle one year after planting with crimson clover.
In any re-vegetation program utilizing non-native species, it is important to ensure that an introduced species will not itself become invasive. For example, Harding grass (Phalaris aquatica) is a perennial bunchgrass native to the Mediterranean region. It was commonly planted as high value pasture forage, but has escaped to colonize wildland areas and displace native species (Harrington and Lanini 2000). Even the use of native species in re-vegetation efforts can present potential problems. Native seed collected in one area of the state but used in a re-vegetation program in a different region may be genetically different, due to ecotypic variability. It has been argued that over time, as a result of genetic contamination, the native population may lose its adaptive advantage in its evolved ecosystem (Knapp and Rice 1997).
Because of the ecological diversity within California, no single species or combination of species will be effective under all circumstances. Although pubescent wheatgrass has proved successful in Siskiyou County, it may not be appropriate in most other areas of the state that lack summer rainfall. Unfortunately, few studies have been conducted on the restoration of yellow starthistle infested grasslands, particularly with native species. Major questions yet to be addressed include what combination of species to use in various environments, which species or combination will aggressively compete with yellow starthistle, and how to economically establish these species. The best re-vegetation strategy is likely to include the use of several species occupying a wide variety of niches in the grassland ecosystem.
