Perennial pastures for marginal farming country in southern Queensland. 2. Potential new grass cultivar evaluation

Trials in the Condamine-Balonne basin, Australia, compared 11 promising perennial pasture grass accessions (4 Bothriochloa, 2 Cenchrus, 2 Urochloa and 1 each of Digitaria, Eragrostis and Panicum species) against the best similar commercial cultivars on the basis of ease of establishment from seed, persistence once established, forage yield and ease of seed production. Accessions sown at a site were determined by prior experience with them on a range of soils. High quality seed was relatively easy to produce for both Urochloa species and for Eragrostis curvula CPI 30374 but problematic for the Bothriochloa spp. Once established, all accessions persisted for 3–5 years and most were well grazed, but adequate establishment was sometimes a problem with Panicum stapfianum and Bothriochloa ewartiana. The dry matter yield ratings of the non-commercial lines were similar to those of the commercial equivalents of the same species. While agronomically valuable, none of the promising new grasses was considered worthy of commercialization at this point because their strengths did not warrant the setting up of a seed-production business in competition with current commercial enterprises. Long-standing cultivars such as Gayndah buffel and Nixon sabi grass continued to exhibit their superior pasture qualities.

Weed dynamics as influenced by tillage system, sowing time and weed competition duration in dry-seeded rice

Cultural practices alter patterns of crop growth and can modify dynamics of weed-crop competition, and hence need to be investigated to evolve sustainable weed management in dry-seeded rice (DSR). Studies on weed dynamics in DSR sown at different times under two tillage systems were conducted at the Agronomic Research Farm, University of Agriculture, Faisalabad, Pakistan. A commonly grown fine rice cultivar 'Super Basmati' was sown on 15th June and 7th July of 2010 and 2011 under zero-till (ZT) and conventional tillage (CONT) and it was subjected to different durations of weed competition [10, 20, 30, 40, and 50 days after sowing (DAS) and season-long competition]. Weed-free plots were maintained under each tillage system and sowing time for comparison. Grassy weeds were higher under ZT while CONT had higher relative proportion of broad-leaved weeds in terms of density and biomass. Density of sedges was higher by 175% in the crop sown on the 7th July than on the 15th June. Delaying sowing time of DSR from mid June to the first week of July reduced weed density by 69 and 43% but their biomass remained unaffected. Tillage systems had no effect on total weed biomass. Plots subjected to season-long weed competition had mostly grasses while broad-leaved weeds were not observed at harvest. In the second year of study, dominance of grassy weeds was increased under both tillage systems and sowing times. Significantly less biomass (48%) of grassy weeds was observed under CONT than ZT in 2010; however, during 2011, this effect was non-significant. Trianthema portulacastrum and Dactyloctenium aegyptium were the dominant broad-leaved and grassy weeds, respectively. Cyperus rotundus was the dominant sedge weed, especially in the crop sown on the 7th July. Relative yield loss (RYL) ranged from 3 to 13% and 7 to16% when weeds were allowed to compete only for 20 DAS. Under season-long weed competition, RYL ranged from 68 to 77% in 2010 and 74 to80% in 2011. The sowing time of 15th June was effective in minimizing weed proliferation and rectifying yield penalty associated with the 7th July sowing. The results suggest that DSR in Pakistan should preferably be sown on 15th June under CONT systems and weeds must be controlled before 20 DAS to avoid yield losses. Successful adoption of DSR at growers' fields in Pakistan will depend on whether growers can control weeds and prevent shifts in weed population from intractable weeds to more difficult-to-control weeds as a consequence of DSR adoption.

Integrated weed management approach to improve weed control efficiencies for sustainable rice production in dry-seeded systems

Weed management is the major challenge to the success of dry-seeded rice (DSR). A field study was conducted during the dry seasons of 2013 and 2014at the International Rice Research Institute to evaluate the performance of herbicides combined with mechanical weeding in DSR. The lowest weed density and biomass were found in the treatment oxadiazon followed by (fb) fenoxaprop+ethoxysulfuron fb 2,4-D fb mechanical weeding (MW) at 42 days after sowing (DAS). However, this treatment had similar weed density and biomass to the treatments oxadiazon fb bispyribac-sodium fb fenoxaprop+ethoxysulfuron fb 2,4-D,oxadiazon fb bispyribac-sodium fb 2,4-D, and oxadiazon fb MW (28 DAS) fb MW (42 DAS). The highest weed density and biomass were recorded in the treatment oxadiazon fb MW (28 DAS) and oxadiazon fb 2,4-D. Higher grain yield (5.3-5.8tha-1) was produced in the plots that received oxadiazon fb fenoxaprop+ethoxysulfuron fb 2,4-D fb MW(42 DAS) and oxadiazon fb bispyribac-sodium fb fenoxaprop+ethoxysulfuron fb 2,4-D. The results of this study provide sustainable weed management options to farmers growing DSR.

Agronomic indices, growth, yield-contributing traits, and yield of dry-seeded rice under varying herbicides

Dry-seeded rice (DSR) is an emerging resource-conserving technology in many Asian countries, but weeds remain the major threat to the production of DSR systems. A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI), Los Baños, Philippines, to evaluate the performance of sole and sequential applications of preemergence (oxadiazon and pendimethalin), early postemergence (butachlor + propanil and thiobencarb + 2,4-D), and late postemergence herbicides (bispyribac-sodium and fenoxaprop + ethoxysulfuron) with different modes of action in comparison to manual weeding in DSR. The sequential applications of all preemergence and postemergence herbicides reduced weed density and biomass by 80–100% compared to the nontreated plots. The sole application of postemergence herbicides reduced weed density by only 44–54% and weed biomass by 51–61%, whereas oxadiazon alone reduced weed density and biomass by 96–100%. All herbicide treatments and manual weeding significantly affected tiller number, biomass, crop growth rate, agronomic indices, yield-contributing parameters (panicle density and filled grains), and yield (biological and grain) of rice. The highest grain yield was obtained in the manually weeded plots (5.9–6.1 t ha−1) and the plots treated with oxadiazon alone (5.4–5.6 t ha−1) and oxadiazon followed by postemergence herbicides (5.2–5.8 t ha−1). The lowest paddy yield (0.22 t ha−1) was achieved in the nontreated plots followed by the plots treated with the sole application of bispyribac-sodium and fenoxaprop + ethoxysulfuron. The results suggest that oxadiazon is the best broad-spectrum and economically effective herbicide when applied alone or in combination with other effective postemergence herbicides with different modes of action, depending on the weed species present in the field.

Efficacy and phytotoxicity of different rates of oxadiargyl and pendimethalin in dry-seeded rice (Oryza sativa L.) in Bangladesh

A field study was established to evaluate oxadiargyl and pendimethalin during the wet seasons in Bangladesh in 2012 and 2013. The study evaluated the following treatments: oxadiargyl applied at 80, 120, and 160 g ai ha−1; pendimethalin at 800, 1200, and 1600 g ai ha−1; partial weedy; and weed-free. Rice plant density was greatly affected by weed control treatment. Lower density and lower uniformity of the rice plant stand occurred as a result of increased rates of herbicides. Increased rates of pendimethalin were more toxic than increased rates of oxadiargyl. Both herbicides effectively controlled Digitaria ciliaris, Echinochloa colona, and Phyllanthus niruri; however, they were unable to control Murdannia nudiflora. Oxadiargyl controlled Cyperus rotundus across rates by 31–55%, but pendimethalin was completely ineffective on it, and higher rates of both herbicides had no effect in controlling this weed. Both herbicides at higher rates reduced total weed biomass significantly. Among herbicide treatments, the highest yield (3.7–4.0 t ha−1) was recorded in plots treated with oxadiargyl at 160 g ai ha−1 and the lowest yield (2.4–2.8 t ha−1) was in plots treated with pendimethalin at 1600 g ai ha−1. Results from our study suggest that a higher rate of oxadiargyl can increase yield by suppressing weeds in dry-seeded rice systems. Similar to the results of oxadiargyl, pendimethalin at higher rates also greatly suppressed weeds; however, yield decreased due to phytotoxicity to rice seedlings.

Weed control in dry direct-seeded rice using tank mixtures of herbicides in South Asia

Dry direct-seeded rice (DSR) faces with complex weed problems particularly when farmers missed pre-emergence herbicide applications. Thus, an effective and strategic weed control in DSR is often required with available options of post-emergence herbicides. In such situations, tank mixtures of herbicides may provide broad spectrum weed control in DSR. Field experiments were conducted in the wet seasons of 2013 and 2014 to study weed control in response to tank mixtures of herbicides currently applied in DSR in South Asia. Results revealed that the tank mixtures of the currently available herbicides (azimsulfuron plus bispyribac or fenoxaprop, bispyribac plus fenoxaprop, and azimsulfuron plus bispyribac plus fenoxaprop; all applied as post-emergence) rarely resulted in antagonistic effects. Highest weed control efficiency (∼98%) was recorded with the tank mixture of azimsulfuron plus bispyribac plus fenoxaprop during both the years. This treatment also produced highest grain yield (7.2 t ha−1 in 2013 and 7.9 t ha−1in 2014), which was similar to the grain yield in the plots treated with the tank mix of azimsulfuron plus fenoxaprop, pendimethalin (applied as pre-emergence) followed by (fb) bispyribac, pendimethalin fb fenoxaprop, as well as pendimethalin fb azimsulfuron. Plots treated with the post-emergence application of single herbicide (i.e., azimsulfuron, bispyribac, or fenoxaprop) had lower grain yield (3.0–5.2 t ha−1 in 2013 to 3.5–6.1 t ha−1in 2014) than all the sequential herbicide treatments and tank mixtures (azimsulfuron plus fenoxaprop and azimsulfuron plus bispyribac), owing to a broad spectrum weed control. The study suggested that if farmers missed the pre-emergence application of herbicides (e.g., pendimethalin) due to erratic rains or due to other reasons, good weed control and high yield can still be obtained with tank mix applications of azimsulfuron plus fenoxaprop or azimsulfuron plus bispyribac plus fenoxaprop in DSR.

Seed bank longevity and age to reproductive maturity of Calotropis procera (Aiton) W.T. Aiton in the dry tropics of northern Queensland

Understanding the reproductive biology of Calotropis procera (Aiton) W.T. Aiton, an invasive weed of northern Australia, is critical for development of effective management strategies. Two experiments are reported on. In Experiment 1 seed longevity of C. procera seeds, exposed to different soil type (clay and river loam), pasture cover (present and absent) and burial depth (0, 2.5, 10 and 20 cm) treatments were examined. In Experiment 2 time to reach reproductive maturity was studied. The latter experiment included its sister species, C. gigantea (L.) W.T. Aiton, for comparison and two separate seed lots were tested in 2009 and 2012 to determine if exposure to different environmental conditions would influence persistence. Both seed lots demonstrated a rapid decline in viability over the first 3 months and declined to zero between 15 and 24 months after burial. In Experiment 1, longevity appeared to be most influenced by rainfall patterns and associated soil moisture, burial depth and soil type, but not the level of pasture cover. Experiment 2 showed that both C. procera and C. gigantea plants could flower once they had reached an average height of 85 cm. However, they differed significantly in terms of basal diameter at first flowering with C. gigantea significantly smaller (31 mm) than C. procera (45 mm). On average, C. gigantea flowered earlier (125 days vs 190 days) and set seed earlier (359 days vs 412 days) than C. procera. These results suggest that, under similar conditions to those that prevailed in the present studies, land managers could potentially achieve effective control of patches of C. procera in 2 years if they are able to kill all original plants and treat seedling regrowth frequently enough to prevent it reaching reproductive maturity. This suggested control strategy is based on the proviso that replenishment of the seed bank is not occurring from external sources (e.g. wind and water dispersal).

Native Phloem and Wood Borers in Australian Mediterranean Forest Trees

Native Mediterranean forests in Australia are dominated by two tree genera, Eucalyptus and Acacia, while Pinus and Eucalyptus dominate plantation forestry. In native forests, there is a high diversity of phloem and wood borers across several families in the Coleoptera and Lepidoptera. In the Coleoptera, cerambycid beetles (Cerambycidae), jewel beetles (Buprestidae), bark, ambrosia and pinhole beetles (Curculionidae) and pinworms (Lymexelidae) are some of the most commonly found beetles attacking eucalypts and acacias. In the Lepidoptera, wood moths (Cossidae), ghost moths (Hepialidae) and borers in the Xyloryctidae (subfamily Xyloryctinae) are most common. In contrast to native forests, there is a much more limited range of native insects present in Australian plantations, particularly in exotic Pinus spp. plantations, although eucalypt plantations do share some borers in common with native forests. This chapter reviews the importance of these borers in Australian forests primarily from an economic perspective (i.e. those species that cause damage to commercial tree species) and highlights a paucity of native forest species that commonly kill trees relative to the large scales regularly seen in North America and Europe.

Fine root dry matter relative to mango (Mangifera indica) tree scion size grafted on size-controlling rootstocks, is negatively related to scion growth rate

Knowledge of root dry matter (DM) allocation, in relation to differing vigour conferred by rootstock cultivars, is required to understand the structural relationships between rootstock and scion. We investigated the mass of roots (four size classes up to 23 mm diameter) by coring proximal to five polyembryonic mango rootstock cultivars known to differ in their effects on the vigour and productivity of scion cultivar ‘Kensington Pride’, in a field trial of 13-year-old trees. Significant differences in fine (<0.64 and 0.64–1.88 mm diameter) and small (1.88–7.50 mm) root DM contents were observed between rootstock cultivars. There was a complex relationship between the amount of feeder (fine and small size classes) roots and scion size (trunk cross sectional area, TCSA), with intermediate size trees on rootstock MYP having the most feeder roots, while the smallest trees, on the rootstock Vellaikulamban had the least of these roots. Across rootstock cultivars, tree vigour (TCSA growth rate) was negatively and significantly related to the ratio of fine root DM/scion TCSA, suggesting this may be a useful indicator of the vigour that different rootstocks confer on the scion. In contrast non-ratio root DM and scion TCSA results had no significant relationships. The significant rootstock effects on orchard root growth and tree size could not be predicted from earlier differences in nursery seedling vigour, nor did seedling vigour predict root DM allocation.