THE IMPACT OF SOIL TYPE AND INCORPORATION WHEN USING FLAME® FOR NUTGRASS MANAGEMENT

TO EXPLAIN conflicting results obtained in field trials in the Mackay district, two pot trials on nutgrass were established in 2013 to study the impact of soil type and incorporation on the efficacy of the pre-emergence herbicide Flame® (imazapic). One pot trial focused on the efficacy of Flame® on nutgrass depending on the soil type. Four common contrasting soil types in Mackay were tested: Victoria Plains (clay, neutral pH, high CEC), Kuttabul (sandy loam, acidic), Calen (sandy clay loam, quite acidic) and Marian (sandy clay loam, low CEC and organic C). The second pot trial tested several incorporations in Marian soil: effective irrigation (to move the herbicide down the soil profile), ineffective light irrigation (herbicide not moving down the soil profile), mechanical incorporation and no incorporation. Both trials were laid out according to a RCB design with 6 replicates. Flame® achieved adequate management of nutgrass when applied in acidic conditions (Kuttabul) or in soil with low CEC and organic C (Marian): phytotoxicity on aerial parts was observed, the number of shoots was reduced by more than 85% and their size reduced by more than 90%, plant biomass was reduced by more than 54%, the production of new tubers was reduced by 99% and their viability by more than 60%. In Calen soil (less acidic, moderate CEC and organic C), Flame® did not perform well: it reduced the production of tubers by 78% and only decreased their viability by 29% whereas other measured parameters were not different to the untreated control. Flame® was not efficient when applied on clay soil with neutral pH and high CEC (Victoria Plains). The efficacy of Flame® on nutgrass varied with the quality of its incorporation. The incorporation by irrigation that moves the herbicide down to the tuber zone was the most efficient option that resulted in 76% less shoots that were 85% smaller, 67% less biomass and 98% less tubers with viability reduced by 73%. No incorporation of the herbicide was the second best option with 54% less shoots that were up to 60% smaller, 50% less biomass and 75% less tubers with viability reduced by 35%. Light incorporation and mechanical incorporation on wet soil resulted in poorer performance. These results will be used to assist growers in using Flame® where the conditions are suitable and recommend better incorporation techniques.