CropLife Australia 2016 Guidelines for Group B Herbicides – Clearfield® Technology High Resistance Risk
Group B resistance exists in Australia in annual ryegrass, barley grass, brome grass, wild oats, paradoxa grass and crabgrass and in at least seventeen broadleaf weeds including wild radish, common sowthistle, black bindweed, charlock, Indian hedge mustard, prickly lettuce, Mediterranean (wild) turnip and turnip weed. Resistance has developed in broadacre, rice and pasture situations. In respect to rice three broadleaf weeds, namely dirty dora, arrowhead and starfruit, are known to have Group B resistant populations.
Research has shown that as few as four applications to the same population of annual ryegrass can result in the selection of resistant individuals and as few as six applications for wild radish. A population can go from a small area of resistant individuals to a whole paddock failure in one season.
A significant challenge facing growers managing Group B resistance is the control of brome grass and barley grass in winter cereal crops. Group B herbicides are presently the only in-crop herbicides that provide effective control of these grass weeds and this poses a severe risk of Group B resistance for growers with cereal dominant rotations.