Development of a method to aid decision making on herbicide use for Australian Canegrowers : SRDC final report BSS186
This project successfully met its objectives. It demonstrated the strong competition effect weed growth has on the yield of sugarcane, developed a robust protocol for the rapid assessment of cane variety reaction to herbicides, and produced a decision aid for growers in the form of a herbicide manual.The importance of controlling weeds in the early crop growth stage of sugarcane was highlighted in all regions from Innisfail to Bundaberg. In trials, it was shown that weed growth early in the crop establishment phase causes significant loss in cane yield of the order of 13% to 50% depending on the period of competition, the weed population and the climatic conditions. Of particular note was the potential crop loss due to weed growth in the first four weeks following emergence of the cane plant. Losses from weed competition were similar over the 1997/98 and 1998/99 seasons.The concept of approaching weed control in young plant cane from the stance of accepting an economic threshold of weed infestation was not achieved. As rainfall has a major influence on windows of opportunity for spraying activity, and therefore the potential for uncontrolled weed growth to influence cane yield, growers are unprepared to accept the potential risk. Growers' attitudes to weed control were assessed through focus groups. They expressed a good qualified, but not quantified, knowledge of weed competition effects. Project results will overcome this deficiency. Growers expressed valid reasons for embracing a zero tolerance to weeds in young plant cane (see section 4.3.1) and why a quadrat would be unsuitable as a decision aid tool (section 188.8.131.52.).A robust technique to evaluate rapidly the phytotoxic effect of herbicides on sugarcane varieties was developed. The technique is valuable because previous methods (large-scale field trials) were resource intensive, subject to a large number of uncontrollable variables, costly and took up to 15 months to complete. The technique was tested over two seasons of trials and is now being used from Tully to Bundaberg as a standard component of the BSES process to develop new sugarcane cultivars. It involves spraying sugarcane setts growing in pots at the 3-4 leaf stage with the candidate herbicides and measuring tillering, shoot elongation and biomass. The completion of trials by 10 weeks allows for the rapid assessment of new herbicides and varieties in a much shorter time frame.The success of the weed competition trials in plant cane resulted in the production of a 'slide-rule' to provide growers with an indication of potential crop and income losses resulting from weed competition. The slide-rule gives a crop yield and income loss for a range of sugar prices and weed-free periods. This brings to growers' attention the magnitude of potential loss due to weeds and has assisted growers with decisions on weed control.A comprehensive manual, intended as the main decision aid tool for canegrowers when making decisions on weed control, was developed, printed and provided to the canegrowing community. It is durable, in a format that allows regular updates, and covers herbicide selection at various stages of growth of the crop, herbicide information and application techniques.