Deeper seeding allows bunchgrass establishment while the pre-emergent berbicide indaziflam controls invasive annual grasses

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Restoration of annual grass-invaded rangelands is often a management priority. Pre-emergent herbicides are an effective restoration tool to reduce annual grasses but can negatively impact seeded vegetation. Hence, seeding is often delayed until herbicide activity has abated. With indaziflam, a pre-emergent with longer soil activity, seeding may need to be delayed for several years. It would be advantageous if seeded species could establish while indaziflam controls annual grasses, as competition with annual grasses would be limited, and forage production and vegetation cover of the soil surface would recover sooner. Seeding deeper in the soil may allow seeded species to largely avoid herbicide activity, but seeded species may struggle to emerge from greater seeding depths. We investigated seeding squirreltail and crested wheatgrass at 1-, 3-, 5-, and 7-cm seeding depths just prior to a fall indaziflam application at two sites in 2 yr. Seeding at ∼1-cm is the recommended practice for both bunchgrasses. Seedling density in late June was greater at the 3 and 5 cm seeding depths and likely greater at the 7 cm depths than at the 1-cm depth. Seedling height was greater at the 3-, 5-, and 7-cm depths than at the 1-cm depth. Seedling density and height did not vary among the 3-, 5-, and 7-cm depths. This suggests that indaziflam largely did not penetrate below the first centimeter or two of the soil the growing season after application. Seeding at depths of 3–7 cm is likely a viable strategy for allowing some seeded species to establish while indaziflam controls annual grasses. Additional evaluations across a gradient of soil and site characteristics, with different plant species and functional groups, and other pre-emergent herbicides are needed to refine this restoration strategy and identify its benefits and limitations.