Assessment of multiple herbicide protection seed treatments for seed-based restoration of native perennial bunchgrasses and sagebrush across multiple sites and years

Abstract

The invasion of exotic, annual plant species is a leading contributor to ecological degradation in drylands globally, and the use of pre-emergent herbicide to control these species is common. Pre-emergent herbicides pose challenges for seed-based restoration due to toxicity to the seeds of desired species. Herbicide protection (HP) technologies pose a potential solution by using activated carbon seed treatments to protect desirable seeds from herbicide exposure. In the sagebrush steppe ecosystem of North America, we used an adaptive small plot design over three planting years to test for effects on seeding outcomes (seedling density and size) of large and small multi-seed HP pellets, several single-seed HP coatings, and carbon banding treatments at geographically dispersed sites for several perennial bunchgrasses and the keystone perennial shrub, Wyoming big sagebrush. We also compared different methods of seed delivery and litter pre-seeding management. Seeding success was low overall, especially for sagebrush, and it was clear that other, often less predictable barriers to establishment than herbicide exposure, such as inadequate spring moisture, were strong drivers of seeding outcomes. Despite this, HP treatments were associated with higher seedling density than bare seed in multiple instances, most notably for grasses. The large HP pellet occasionally outperformed the small HP pellet, and several HP coatings performed similarly to the small pellet. Surprisingly, we did not see consistent negative effects of pre-emergent herbicide on unprotected bare seed. We conclude that HP seed treatments show some promise to improve seeding success in the presence of herbicide, but that consistent success will require further improvements to HP treatments as well as integration with other innovations and approaches.

Evaluating Seed Enhancement Technology’s Effects on Seed Viability during Multi-Year Storage: A Case Study Using Herbicide Protection Pellets

“…The seed of A. tridentata germinated better after storage as bare seed than when made into and recovered from new HPPs or recovered from old HPPs produced before storage, though old HPPs had the smallest decline in germinability. This generally supports the findings of prior studies incorporating A. tridentata seeds into HPPs, which have also observed overall negative effects of the technology on this small-seeded, perennial shrub species [18,21]. Interestingly, our findings imply that even though storage of bare seed in refrigerated conditions is recommended for this species and resulted in the maintenance of relatively high germinability of bare seed (75%), this may not be needed once the seed is made into pellets.…”

“…The future of HPP technology as an at-scale tool for restoration of many species is unclear, with additional trials and refinements still needed [8,12,18]. Additionally, another method to apply activated carbon to seeds, namely seed coating, is under investigation [16][17][18]23].…”

“…This treatment is designed to allow seedling establishment during the period of maximum herbicide efficacy and, thus, lowest competition with targeted weeds [12,13]. Production of this technology involves combining seed with activated carbon and other binders into either multi-seed pellets via a wet extrusion pelleting process identical to the production of pasta [13][14][15], or into single-seed coatings [16][17][18] via rotary or pan coating techniques commonly used in the application of other seed coatings [9].…”

Delayed seeding and nutrient amendment seed enhancement technology: potential to improve sagebrush establishment?

“…Seedlings in the dust treatments showed no such cost, with similar emergence to bare seed, while pellet treatments had an average emergence 6.3 times lower than bare seed. This reduction in emergence could be due to insufficient sunlight reaching the seeds, compaction of the seeds, or a physical barrier preventing seedlings from sprouting, and are consistent with other trials using similar treatments (Baughman et al 2023; Eshleman & Riginos 2023). Multiple results now indicate that extruded pellets do not effectively deliver amendments to sagebrush.…”

“…We installed plots on northern slopes to take advantage of greater moisture throughout the growing season. Three furrows, 2.5 cm wide and 1.25–2 cm deep, were dug by hand lengthwise in each plot based on previous trials showing that sagebrush has more success growing from furrows than from broadcasted seed (Baughman et al 2023). Treatments were applied randomly across plots at a rate of 200 pure live seeds (PLS) per plot, and all seed treatments were applied on the soil surface within the furrows.…”