Kochia (Bassia scoparia) harvest date impacts nutrient composition, in vitro degradability, and feed value more than pre-harvest herbicide treatment or herbicide resistance traits

Abstract Kochia is a summer-annual tumbleweed that is drought, saline, and heat tolerant, and often resistant to several herbicides. Glyphosate-resistant kochia exhibits indeterminate growth and remains green during senescence, making it difficult to harvest crops that are contaminated with this weed. Removing dense patches of kochia from contaminated crops can aid in downstream harvest operations while also generating a potential source of livestock feed. This study evaluated the effects of two kochia populations [glyphosate-resistant (GR) and glyphosate-susceptible (GS) kochia] with or without pre-harvest treatment using glyphosate + saflufenacil [untreated (UN) vs treated 10 d pre-harvest (PRE)] on nutrient composition and in vitro degradability when it was harvested at advancing maturities. Kochia (GR-UN, GR-PRE, GS-UN, and GS-PRE) was harvested on 6 dates (HD) corresponding to pre-bloom (HD 1), mid-bloom (HD 2), full-bloom with 50% open flowers (HD 3), developing seeds (HD 4), mid-mature seeds (HD 5) and fully mature seeds (HD 6). In most cases, harvest date affected the chemical composition and in vitro degradability to a greater extent than the kochia population or herbicide treatment. The dry matter (DM) yield increased (P