Crop rows oriented at a right angle to sunlight direction (i.e., east–west within the winter cropping system in Western Australia) may suppress weed growth through greater shading of weeds in the interrow spaces. This was investigated in the districts of Merredin and Beverley, Western Australian (latitudes of 31° and 32°S) from 2002 to 2005 (four trials). Winter grain crops (wheat, barley, canola, lupines, and field peas) were sown in an east–west or north–south orientation. Within wheat and barley crops oriented east–west, weed biomass (averaged throughout all trials) was reduced by 51 and 37%, and grain yield increased by 24 and 26% (compared with crops oriented north–south). This reduction in weed biomass and increase in crop yield likely resulted from the increased light (photosynthetically active radiation) interception by crops oriented east–west (i.e., light interception by the crop canopy as opposed to the weed canopy was 28 and 18% greater in wheat and barley crops oriented east–west, compared with north–south crops). There was no consistent effect of crop row orientation in the canola, field pea, and lupine crops. It appears that manipulation of crop row orientation in wheat and barley is a useful weed-control technique that has few negative effects on the farming system (i.e., does not cost anything to implement and is more environmentally friendly than chemical weed control).

Postdispersal weed seed predation by animals during the summer fallow period may lead to a reduction in the number of weeds that grow in the following winter cropping season. In this study, we investigated the patterns of weed seed removal, the influence of crop residue cover on seed removal, the types of granivores present and their seed preferences in a 16-ha postharvest cropping field in Western Australia during the summer months over 2 yr. Seed removal from caches was extremely variable (from 0 to 100%). Removal rates were generally highest along the edges of the field near bordering vegetation and lowest in the center of the field and within the bordering vegetation. However, there were many deviations from this general pattern. There was no change in rates of predation with different levels of residue cover. Ants or other small invertebrates were found to remove the most seeds. However, seed removal by other animals, such as rodents, was also evident. Annual ryegrass seeds were preferred over wild oat seeds, followed by wild radish pod segments. Seed harvesting was lowest in late January, peaked in February, and decreased in March. Results from this study suggest seed harvesters could reduce the number of surface seeds in the field, reducing the weed seed bank. Management options that increase the activity of the seed harvesters may lead to less variability in seed predation and could, therefore, be incorporated into an integrated weed management program.

PRE herbicides are less effective in the zero-tillage system because of increased residual crop stubble and reduced soil incorporation. However, since weeds are not physically controlled in the zero-tillage system, reliance on efficacy of PRE herbicides is increased. This research investigated the impact of carrier volume and droplet size on the performance of PRE herbicides (in wheat crops at four sites in 2010) to improve herbicide efficacy in conditions of high stubble biomass in zero-tillage systems. Increasing carrier volume from 30 to 150 L ha−1increased spray coverage on water-sensitive paper from an average of 5 to 32%. Average control of rigid ryegrass by trifluralin (at Cunderdin and Merredin sites) and trifluralin or pyroxasulfone (at Wickepin and Esperance sites) improved from 53 to 78% with increasing carrier volume. Use of ASABE Medium droplet size improved spray coverage compared with ASABE Extremely Coarse droplet size, but did not affect herbicide performance. It is clear that increased carrier volume improves rigid ryegrass weed control for nonwater-soluble (trifluralin) and water-soluble (pyroxasulfone) PRE herbicides. Western Australian growers often use low carrier volumes to reduce time of spray application or because sufficient high-quality water is not available, but the advantages of improved weed control justifies the use of a high carrier volume in areas of high weed density.

Summary1. Abscission of seeds in some plant species occurs as a result of strong wind gusts that exert sufficient drag forces to liberate the seed from its parent. This may be an adaptive feature, as release into stronger wind gusts has been shown to lead to greater dispersal distances, which is likely to have evolutionary advantages. 2. We test the hypotheses that (i) seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations and (ii) that the preferential abscission of seeds into upward wind gusts will result in the dispersal of seeds over greater distances. 3. As a case study, we studied the abscission dynamics of Conyza bonariensis (L.) Cronquist (fleabane), which is an important weed with global distribution. Using abscission data obtained through a series of seed release experiments, we confirm that abscission of seeds in C. bonariensis is most likely to occur during strong and upward wind gusts. 4. We demonstrate that, for a given wind speed, seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations. We also show that preferential release into upward wind gusts has some influence on the distance travelled, but the strength of this influence is dependent on the correlation between wind orientation and wind speed. For this particular study, the sensitivity of release to the horizontal wind speed seems to have a larger effect on the distance travelled than sensitivity to wind orientation.

Summary1. It has been established that the timing of abscission has a major impact on the dispersal distances achieved by individual seeds, and yet there is little information available on seed release thresholds. 2. The current research used Conyza bonariensis to examine seed release thresholds of seed heads at varying ages and at varying orientations (in relation to the direction of the air flow). 3. Wind speeds of 0-70 m s À1 were used to remove the seeds from seed heads harvested directly prior to exposure to wind. Seed head age at the time of harvest from the plant (0-10 days old, where day 0 is the day on which the seed head opens) and seed head orientation (in relation to the direction of air) were altered. 4. While seed loss increased with increasing wind speed, average loss from seed heads increased from 49·4% on the day they opened to 92·8% from seed heads open for 10 days. Further, there was an average seed loss of 76·4%, 72·5%, 73·9%, 65·3% and 58·8% for wind orientations of 0, 45, 90, 135 and 180°, where 0°indicates wind directed up towards the base of the hemispherical seed head (simulating an updraft), 90°indicate wind directed towards the side of the seed head (horizontal wind) and 180°indicate wind directed down towards the top of the seed head (simulating a downdraft). 5. Seeds were released in the strongest wind events and were more likely to be released in updrafts or horizontal winds rather than downdrafts. Both of these factors interact with seed aging in a way that will increase the potential dispersal distance. Given that minor changes to abscission can have major impacts on maximum dispersal distance; these factors need to be taken into account when formulating models on dispersal. 6. This research supports the theory that where greater dispersal confers an evolutionary advantage, wind-dispersed plants would be likely to evolve strategies to ensure maximum dispersal capability.