Photosystem II Inhibitor Resistance in the Columbia Basin of Washington State

Abstract

Weed management in potato and mint rely heavily on two Group 5 photosystem II–inhibiting herbicides, metribuzin and terbacil, respectively. Seed from weed escapes was collected in 2010 from 69 potato and mint production fields in Washington State and tested for resistance to metribuzin and terbacil. Of the seed screened, 26 of 51 Powell amaranth and redroot pigweed accessions and 8 of 23 common lambsquarters accessions tested expressed at least some degree of resistance to one or both herbicides. A Ser264Gly mutation in the chloroplastpsbA gene was present in all but three resistant accessions. Herbicides with other mechanisms of action registered in potato and mint controlled all identified photosystem II–resistant accessions when applied at typical labeled rates.