A survey of fallow practices and weed floras in wheat stubble and grain sorghum in northern New South Wales.

A survey undertaken in northern New South Wales after the 1989 wheat harvest investigated the effects of cultural practices used by dryland farmers on summer weed flora. Only 50% of fallow paddocks surveyed between December and February were weedfree, and by mid January 65% had inadequate stubble cover (<1000 kg/ha) for protection from soil erosion, mainly because of excessive tillage. By February, only 10% of paddocks were being sprayed with a herbicide to control weeds. Examination of 65 uncultivated fallow wheat stubble paddocks and 25 grain sorghum crops identified 87 and 51 different weed species, respectively. In fallow paddocks where no herbicide had been used, 69 and 61 species were found in ungrazed and grazed paddocks, respectively. Where glyphosate had been used the number of species was 37 (grazed) and 39 (ungrazed), and for glyphosate plus atrazine, 23 and 18 species. The number of weed species found in grain sorghum was 29 for cultivated without atrazine, 35 for cultivated with atrazine, and 35 for no-tillage with atrazine, The most important weeds found in fallow were liverseed grass, native millet, common sowthistle, wireweed, and barnyard grasses. Black bindweed was a problem where atrazine had not been used. Native millet was the most abundant species where atrazine had been applied. In grain sorghum the most common broadleaf weeds for cultivated paddocks with no atrazine treatment were Tribulus spp., Australian bindweed, pigweed, and Bathurst burr, while the most common grass weeds were barnyard grasses, liverseed grass, stinkgrass, and native millet. When cultivation plus atrazine was used, barnyard grasses, native millet, wild oats, and liverseed grass were the most common weeds. In minimum tillage or no-tillage paddocks treated with atrazine, native millet, Queensland blue grass, liverseed grass, common sowthistle, Australian bindweed, and windmill grass were the most common weeds.