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

Abstract

Natural resource managers commonly use herbicides to control invasive weeds. This practice, however, can lead to secondary invasion by other invasive plants, unless measures such as seeding are taken to promote natives. Although there is evidence that seeding immediately after herbicide treatment adversely affects germination, there is little information on optimal timing between spraying and seeding or variation among species in herbicide sensitivity. We investigated effects of picloram and aminopyralid on seed performance of 10 native plants. We separated the herbicide application and seeding by 0, 3, 6, 9, and 11 months in a greenhouse, and recorded the rates of germination and germinant biomass after 6 weeks. In addition, we installed 72 field plots to test the effects of fall-and spring-treated plots on seed performance. In the greenhouse, herbicides negatively impacted germination of four species over the entire 11-month trail whereas six showed less sensitivity over time. Results from spring-treated field plots were largely consistent with those from the greenhouse: rates of germination and biomass were lower in herbicide-treated plots than those in control plots for 75% of seeded species. In fall-sprayed plots, however, the adverse effects of herbicides were only apparent for 25% of seeded species. Results from greenhouse and field studies combined indicate that herbicides can have strong adverse effects on germination, but that actual effects in field settings will be based on complex interactions between species traits, field conditions, and management choices. Thus, site-specific trials will ultimately be the best method for making inference to particular restoration sites. Key words: aminopyralid, invasive plants, natural areas management, nontarget effects, picloram, secondary invasion Implications for Practice• Our finding of species-specific variation in magnitude and duration of herbicide-treatment impacts suggests the need for herbicide-specific seed mixes that include species observed to have greater tolerance to growing in herbicide-treated soils. • Results from the greenhouse and field indicate that using aminopyralid-based products over picloram-based products to control target invaders, when appropriate, may reduce the severity and duration of herbicide residual effects on seeded species. • Observed differences in herbicide impacts on seeds between the greenhouse and field trials suggest that while greenhouse studies can reveal maximum potential effects, field trials are needed to determine potential realized effects on each target species, due to complex interactions between field conditions, management choices, and soil type.

Evaluating winter annual grass control and native species establishment following applications of indaziflam on rangeland

“…Revegetation is not only very costly and labor-intensive, but often fails in western climates where moisture events are scarce and unpredictable (Ethridge et al 1997;Mangold and Parkinson 2015;Young 2000). Herbicides used in the restoration process can also negatively impact desirable seeded species, preventing successful establishment (Lym et al 2017;McManamen et al 2018;Morris et al 2009;Sbatella et al 2011;Shinn and Thill 2004).…”

Do No Harm: Efficacy of a Single Herbicide Application to Control an Invasive Shrub While Minimizing Collateral Damage to Native Species

“…As a dominant exotic is reduced in abundance, biotic filters may be relaxed as niche space becomes available. In addition, if appropriate control of an exotic is obtained, supplemental seed additions of native species may drive establishment of a diverse native community resistant to reinvasion of the exotic [10,11]. Such seed additions can offer an opportunity to increase the abundance of desirable species [12].…”

Inoculation with native grassland soils improves native plant species germination in highly disturbed soil

“…Zhang et al, 2021). Furthermore, restoration strategies to eradicate nonnative plants often include mechanical or chemical removal of the invasive species, and these intensive management practices may also impede germination of native species (Hu et al, 2021;McManamen et al, 2018;Wagner & Nelson, 2014). While it is well documented that anthropogenic disturbances have adverse effects on soil microbial communities, the importance of re-establishing native microbial communities is seldom considered in ecological restorations (Koziol et al, 2021), and few studies have assessed effective strategies to enhance germination of desirable species in highly degraded soils.…”