Seeding Rate, Planting Date, and Herbicides for Dormant Seeded Safflower in Utah

Dryland crop production in the Intermountain West is largely limited by the amount of precipitation received. Increasing dryland safflower (Carthamus tinctorius L.) production yields in a semi-arid climate is possible with a dormant planting but is not well understood. A two-year (2020-22) project was designed to gain an understanding of the effects of variety, seeding rate, and planting date, on dormant seeded safflower. Chemical weed control options for safflower were also evaluated. One study, conducted at three Utah State University research farms near Blue Creek, Clarkston, and Kaysville, UT, evaluated four varieties, S-208, S-333, 7325 and Hybrid-446, seeded at five rates and planted in the fall and spring. Safflower was sown at 6.7 (spring only), 13.5, 20.2, 26.9, 33.6, and 40.4 (fall only) kg ha-1. Fall seeded safflower had lower plant densities but an increase in pods per plant when comparing identical seeding rates of both planting dates. At Kaysville, all four varieties displayed an increase in seed yield with fall planting during both years of the study. Seed quality differed in oil content among varieties with Hybrid-446 being lower (32-34%). Planting at lower seeding rates tended to result in higher seed oil content. Greatest yields for fall planting were achieved with a seeding rate of 20.2 kg ha-1. Another experiment conducted at Blue Creek and Clarkston, UT, evaluated chemical weed control options. Treatments comprised of herbicide(s) used, timing of application and rate applied. In general, fall applications gave the same, and at times better, control of Russian thistle (Salsola tragus L.), prickly lettuce (lactuca serriola L.), kochia (Bassia scoparia L.) and volunteer wheat (Triticum aestivum L.), compared to spring applications. Overall, liquid ethalfluralin or the highest rates of sulfentrazone (280 to 560 g ha-1) applied in the fall, demonstrated reasonable control of weeds. Greatest yields (515 kg ha-1) came from plots treated with highest rates of sulfentrazone following planting in the fall. Results suggest an optimal seeding rate of 20.2 kg ha-1, with ethalfluralin or sulfentrazone effectively managing weeds. Compared to spring, fall planting will have reduced stand establishment, but increased pods plant-1, which may result in increased yield.