Dicamba-resistant (DR) kochia [Bassia scoparia (L.) A. J. Scott] has been reported in six U.S. states and one Canadian province. To develop effective B. scoparia control tactics, it is necessary to understand the seed germination pattern of DR B. scoparia. The objective of this study was to compare the germination characteristics of DR versus dicamba-susceptible (DS) B. scoparia populations from Montana and Kansas under constant (5 to 35 C) and/or alternating temperatures (5/10 to 30/35 C). DR B. scoparia lines from Montana were generated after three generations of recurrent selection of field-collected populations with dicamba. Seeds of DR or DS lines from Kansas were obtained after one generation of restricted self-pollination. DR B. scoparia lines from both Montana and Kansas had a lower maximum cumulative germination than the DS lines across all temperature treatments. A majority of DR B. scoparia lines from Montana showed a temperature-mediated seed germination response, with a higher thermal requirement (30 to 35 C or 25/30 to 30/35 C) to attain the maximum cumulative germination compared with DS lines. Germination rates at 5 to 30 C were lower for DR versus DS B. scoparia lines from Kansas. All DR lines from Montana took more time than DS lines to initiate germination at 5 and 10 C or 5/10 and 20/25 C. Similarly, there was a delayed onset of germination of the DR versus DS line from Kansas at 5, 10, 15, and 20 C. Furthermore, the DR B. scoparia from both Kansas and Montana had a slower germination pattern relative to the DS B. scoparia. Diversified crop rotations using winter wheat (Triticum aestivum L.), fall-sown cover crops, or early-spring planted crops (e.g., wheat or barley [Hordeum vulgare L.]) that are competitive against lateemerging B. scoparia in conjunction with strategic tillage and late-season weed control tactics should be used to facilitate depletion of DR B. scoparia seedbanks.
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Vol. 66 • No. 6