Survey of weed flora and management relative to cropping practices in the north-eastern grain region of Australia

The main weeds and weed management practices undertaken in broad acre dryland cropping areas of north-eastern Australia have been identified. The information was collected in a comprehensive postal survey of both growers and agronomists from Dubbo in New South Wales (NSW) through to Clermont in central Queensland, where 237 surveys were returned. A very diverse weed flora of 105 weeds from 91 genera was identified for the three cropping zones within the region (central Queensland, southern Queensland and northern NSW). Twenty-three weeds were common to all cropping zones. The major common weeds were Sonchus oleraceus, Rapistrum rugosum, Echinochloa spp. and Urochloa panicoides. The main weeds were identified for both summer and winter fallows, and sorghum, wheat and chickpea crops for each of the zones, with some commonality as well as floral uniqueness recorded. More genera were recorded in the fallows than in crops, and those in summer fallows exceeded the number in winter. Across the region, weed management relied heavily on herbicides. In fallows, glyphosate and mixes with glyphosate were very common, although the importance of the glyphosate mix partner differed among the cropping zones. Use and importance of pre-emergence herbicides in-crop varied considerably among the zones. In wheat, more graminicides were used in northern NSW than in southern Queensland, and virtually none were used in central Queensland, reflecting the differences in winter grass weed flora across the region. Atrazine was the major herbicide used in sorghum, although metolachlor was also used predominantly in northern NSW. Fallow and inter-row cultivation were used more often in the southern areas of the region. Grazing of fallows was more prominent in northern NSW. High crop seeding rates were not commonly recorded indicating that growers are not using crop competition as a tool for weed management. Although many management practices were recorded overall, few growers were using integrated weed management, and herbicide resistance has been and continues to be an issue for the region.

Impact of tillage and residues from rotation crops on the nematode community in soil and surface mulch during the following sugarcane crop.

The impact of three cropping histories (sugarcane, maize and soybean) and two tillage practices (conventional tillage and direct drill) on plant-parasitic and free-living nematodes in the following sugarcane crop was examined in a field trial at Bundaberg. Soybean reduced populations of lesion nematode (Pratylenchus zeae) and root-knot nematode (Meloidogyne javanica) in comparison to previous crops of sugarcane or maize but increased populations of spiral nematode (Helicotylenchus dihystera) and maintained populations of dagger nematode (Xiphinema elongatum). However the effect of soybean on P zeae and M. javanica was no longer apparent 15 weeks after planting sugarcane, while later in the season, populations of these nematodes following soybean were as high as or higher than maize or sugarcane. Populations of P zeae were initially reduced by cultivation but due to strong resurgence tended to be higher in conventionally tilled than direct drill plots at the end of the plant crop. Even greater tillage effects were observed with M. javanica and X. elongatum, as nematode populations were significantly higher in conventionally tilled than direct drill plots late in the season. Populations of free-living nematodes in the upper 10 cm of soil were initially highest following soybean, but after 15, 35 and 59 weeks were lower than after sugarcane and contained fewer omnivorous and predatory nematodes. Conventional tillage increased populations of free-living nematodes in soil in comparison to direct drill and was also detrimental to omnivorous and predatory nematodes. These results suggest that crop rotation and tillage not only affect plant-parasitic nematodes directly, but also have indirect effects by impacting on natural enemies that regulate nematode populations. More than 2 million nematodes/m(2) were often present in crop residues on the surface of direct drill plots. Bacterial-feeding nematodes were predominant in residues early in the decomposition process but fungal-feeding nematodes predominated after 15 weeks. This indicates that fungi become an increasingly important component of the detritus food web as decomposition proceeds, and that that the rate of nutrient cycling decreases with time. Correlations between total numbers of free-living nematodes and mineral N concentrations in crop residues and surface soil suggested that the free-living nematode community may provide an indication of the rate of mineralisation of N from organic matter.