|SPRING, JOHN - Washington State University|
|BURKE, IAN - Washington State University|
Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2016
Publication Date: 9/28/2016
Citation: Spring, J.F., Boydston, R.A., Burke, I.C. 2016. Photosystem II inhibitor resistance in the Columbia Basin of Washington State. Weed Technology. 30:783-792.
Interpretive Summary: Potato and mint (peppermint and spearmint) are commonly produced in the irrigated regions of the Pacific Northwest and both crops rely heavily on herbicides that inhibit photosystem II (PSII) in plants; metribuzin (in potato) and terbacil (in mint) for weed management. Weeds have developed resistance to this group of herbicides when they are used repeatedly and frequently in crop rotations with 98 different weed species being reported word-wide. From a management perspective, it is important to determine if weed control failures result from the presence of herbicide resistance or from other factors. No systematic investigation for herbicide resistance to these herbicides in potatoes and mint has previously been conducted in Washington State. Seed was collected from Powell amaranth, redroot pigweed, and common lambsquarters from escape weeds in potato and mint production fields in Washington and tested for resistance to metribuzin and terbacil. Initial screening indicated that 9 of 14 Powell amaranth samples, 16 of 33 redroot pigweed samples, and 8 of 22 common lambsquarters samples were resistant to either metribuzin or terbacil. The vast majority of accessions were resistant to both herbicides. Dose response studies determined that it required 2 to 104 times more metribuzin and 2 to 40 times more terbacil to control the resistant plants compared to the susceptible plants. A common mutation was present in 88% of the resistant redroot pigweed samples and in all of the resistant common lambsquarter. Other herbicides registered in potato and mint with different mechanisms of action were able to control the PSII resistant plants. When possible, growers should eliminate weeds that escape herbicide treatments to prevent seed production and delay development of herbicide resistant populations. Tank mixing and rotating with herbicides having a different mechanism of action along with hand weeding of escape weeds should be practiced both in season and through crop rotations to deter further development of herbicide resistant weeds.
Technical Abstract: Potato and mint (peppermint and spearmint) are commonly produced in the irrigated regions of the Pacific Northwest and both crops rely heavily on photosystem II (PSII) inhibitor herbicides metribuzin (potato) and terbacil (mint) for weed management. Seed was collected in 2010 from Powell amaranth, redroot pigweed, and common lambsquarters in potato and mint production fields in central Washington and tested for resistance to metribuzin and terbacil. Initial screening indicated that 9 of 14 Powell amaranth accessions, 16 of 33 redroot pigweed accessions, and 8 of 22 common lambsquarters accessions were resistant to either metribuzin or terbacil. Dose response trials confirmed the results of the initial screening and that all but one redroot pigweed and one Powell amaranth accession were cross-resistant to metribuzin and terbacil. All 8 of the PSII resistant common lambsquarters accessions were cross resistant to both herbicides. Resistance index (RI) based on GR50 for weed biomass varied from 2 to 104 for metribuzin and 2 to 16 for terbacil in the Powell amaranth and redroot pigweed accessions. RI varied from 23 to 83 for metribuzin and 18 to 40 for terbacil in the common lambsquarters accessions. A Ser264Gly mutation in the chloroplast psbA gene was present in 7 of the 9 resistant Powell amaranth accessions, 15 of the 16 resistant redroot pigweed accessions, and in all 8 of the resistant common lambsquarters accessions. The level of resistance was lower in three resistant Powell amaranth and redroot pigweed accessions without the Ser264Gly mutation (RI ranging from 4 to 7 for metribuzin and 1 to 3 for terbacil). Other mechanism of action herbicides registered in potato and mint with activity on these three weed species were able to control all PSII resistant accessions.