Evaluating different rates of activated carbon in commercially produced seed coatings in laboratory and field trials

Abstract

Pre‐emergent herbicides, commonly employed for managing invasive annual plants, often fail to meet restoration targets due to the absence of remnant perennial plants, which leaves sites vulnerable to re‐invasion and hinders effective control of annual grasses. Combining an herbicide treatment with seeding is therefore desirable, but seeded plants can also be negatively impacted by pre‐emergent herbicides. Herbicide protection (HP) seed technologies use activated carbon to adsorb herbicide near seeds and have shown promise for allowing simultaneous deployment of herbicide and seed, but recent research recommends numerous additional refinements be tested. We addressed some of these recommendations through one laboratory and a field trial replicated at multiple sites to explore whether commercially produced, single‐seed HP coatings with two different rates of activated carbon can prevent herbicide‐related damage to two perennial bunchgrasses native to the western United States. We also investigated how these coated prototypes compare in performance to the multi‐seed extruded herbicide protection pellets (HPPs) tested in prior research. In the laboratory, neither coating treatment reduced total emergence, emergence rate, survival, or biomass in the absence of herbicide. In the presence of herbicide, both provided several‐fold higher survival and aboveground biomass compared to untreated bare seed, but this represented incomplete protection from herbicide. In field trials where conditions were harsher than the laboratory, we found no evidence of HP from any treatment, and HPPs reduced seedling count for one species. We conclude that the tested HP coating prototype is an improvement over HPPs but requires additional refinements and testing.