Grass Response to Picloram and Clopyralid Applied Before Seeding¹

Abstract

Reduction of weed competition using herbicides is critical to the successful revegetation of weed-infested rangeland. However, little is known about the influence of persistent broadleaf herbicides on the establishment of many desired grasses. The objective of this study was to determine the influence of various rates and times of application of picloram and clopyralid before seeding on two native and two nonnative grasses important to western United States rangeland. The study was conducted in 1997 and 1998 in Wyoming, Montana, and Washington. Five herbicide treatments (none, picloram at 0.14, 0.28, 0.56 kg ai/ha, clopyralid at 0.14, 0.56 kg ai/ha), three timings of herbicide application (44, 24, and 0 d prior to seeding[DPS]), and four grass species (Idaho fescue, bluebunch wheatgrass, crested wheatgrass, and pubescent wheatgrass) were factorially arranged in a randomized split-plot design with three blocks. The whole-plots were the seeded grass species, and the subplots were the herbicide treatments and timings of application. Treatments were performed in the spring of 1997. Treatment effects on grass vigor (1997) and biomass (1998) depended on grass species, herbicide and rate, and timing. Idaho fescue established at low densities, and it was not possible to determine the treatment effects. In general, crested and pubescent wheatgrass had higher vigor estimates and biomass than did bluebunch wheatgrass. Herbicide applied 24 or 44 DPS had less effect on grass vigor and biomass than did herbicide applied at seeding. Picloram at 0.28 and 0.56 kg/ha tended to reduce vigor and biomass more when compared with the 0.14 kg/ha rate and with both rates of clopyralid. On the basis of these experiments, applying picloram or clopyralid at rates as high as 0.56 kg/ha 24 d or more before seeding bluebunch wheatgrass, pubescent wheatgrass, or crested wheatgrass may allow effective weed control and long-term management through grass competition.

Effect of picloram herbicide on physiological responses of Eupatorium adenophorum Spreng

“…Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) is a systemic chlorinated herbicide, known as a synthetic auxin. This herbicide is widely used in many countries because of the high efficiency in the control of broadleaf weed and woody plants in pasture, wheat, rice, barley, sugarcane, and other crop fields (Sheley et al, 2002;Nelson and Lym, 2003;Dos Santos and Masini, 2007). As a selective herbicide, many researchers have studied its mechanisms of action on plants (Ortega and Pearson, 2011;Smitha and Nair, 2011).…”

Timing of seeding after herbicide application influences rates of germination and seedling biomass of native plants used for grassland restoration

“…In contrast, in the greenhouse all of these species had significantly lower germination in treated compared to control pots, even when seeded into soil that had been treated nearly 1 year before seeding. Results of previous studies of the short‐term effects of herbicides on germination in field settings have been variable: some investigators have found that herbicide treatments did not significantly impact the germination of subsequent seed additions (Sheley et al ; Douglass et al ), while others reported negative effects (Lym & Messersmith ; Ortega & Pearson ; Endress et al ). The difference in results between our greenhouse and field environments, coupled with variable findings from other field studies, suggests that results from greenhouse experiments may represent a maximum potential impact for aminopyralid and picloram treatments at the germination stage, while field results may represent realized and more variable effects of those herbicides for particular field sites.…”

“…To our knowledge, the only other study that addressed timing of herbicide treatments and seeding of native species in a natural area also found that timing was important for seedling establishment. Sheley et al (), in a 44‐day study of effects of herbicides on graminoids, reported that delaying seeding by 24 or 44 days after herbicide application improved the vigor of several desirable species by 40% in comparison to seeding immediately after application. The positive effect of seeding delay on seed performance of some of the species found in our study adds to a small but growing body of evidence that suggests that timing of integrated management strategies may be critical for successful establishment of species seeded for restoration in invaded areas.…”

“…Herbicide damage to graminoids at the seed stage may be due to lack of morphological features, such as leaf sheaths that protect adults from the herbicides (Cobb & Reade ). Despite observed adverse effects on both forbs and graminoids, there is also some evidence that at low concentrations synthetic auxin herbicides can have positive effects on some species at certain life stages due to increased protein synthesis or increased cytoplasmic streaming and stem elongation (Hsueh & Lou ; Chang & Foy ; Sheley et al ). As broadleaf‐selective herbicides are among the most commonly used for invasive plant reduction for natural areas management and restoration (Wagner et al ) and because these chemicals often remain active in soil long enough to impact timely seed additions, it is imperative that managers better understand the implications of using these herbicides in areas where recovery of native plant populations is a goal.…”

Native Grass Establishment using Journey®Herbicide

“…Introduction and establishment of competitive native plants is critical for the sustainable management of weed infestations and the rehabilitation of desirable ecosystems (Jacobs et al 1999). Seeding perennial grasses following herbicide application can increase establishment and provide sustained weed control through grass competition (Bornman et al 1991;Sheley et al 2002;Barnes 2004;.…”