The Effects of Temperature and Soil Moisture on Chickpea ('Cicer arietinum L.') Genotype Sensitivity to Isoxaflutole
Isoxaflutole at 75 g ai ha⁻¹ is registered in Australia for the control of several broadleaf weeds in chickpea ('Cicer arietinum L.'). Although isoxaflutole provides satisfactory control of problematic weeds, under certain conditions crop injury can occur. Higher air temperature and moisture content of soil are reported to affect the metabolism of soil applied herbicide. Controlled environment experiments were used to determine the tolerance of chickpea to isoxaflutole under a range of temperature and soil moisture levels. For the soil moisture study, the variables examined were two desi chickpea genotypes (Kyabra as a tolerant cultivar and Yorker as a sensitive cultivar), three soil moisture levels [50 % field capacity (FC), 75 % FC and FC] with three herbicide rates [0, 75 (recommended rate) and 300 g ai ha⁻¹]. For the temperature by soil moisture study, the variables examined were two other desi chickpea genotypes (97039-1275 as a tolerant line and 91025-3021 as a sensitive line), three temperature regimes (20/5, 30/15 and 35/25 °C), two soil moisture conditions (50 % FC and FC) with the same three herbicide rates. The results demonstrated that the chickpea genotypes exhibited differential tolerance to isoxaflutole, but that differences in response were affected by rate, temperature and soil moisture. Increasing temperature and soil moisture content made the susceptible chickpea genotype more vulnerable to isoxaflutole damage. Injury to the susceptible genotype in terms of increased leaf chlorosis and reduction in shoot height and dry matter production increased as soil moisture increased from 50 % FC to FC and temperature increased from 20/5 to 35/25 °C. Overall damage of the sensitive genotype from increasing rates of isoxaflutole also increased when soil moisture content increased from 50 % FC to FC within the fixed temperature regime of 30/15 °C. The sensitivity of chickpea to isoxaflutole depends on existing temperature and moisture content and the chances of crop damage were enhanced with increasing temperature and moisture levels.
Improving competitive ability of chickpea with sowthistle
An experiment was conducted to examine the extent of root and canopy interference of chickpea with sowthistle. In this experiment sowthistle was surrounded with either two or eight chickpea plants according to the following partitioning regimes: full competition, shoot competition, and root competition. The performance of sowthistle grown in full competition with two chickpea plants was the same as those grown in root competition only. Also, there were no significant differences between sowthistle grown under the canopy of two chickpeas and the control ones, where there was no competition. On the other hand sowthistle grown with eight chickpea plants were significantly suppressed in full, canopy or root competition. It was concluded that the roots of the chickpea cultivar tested were sufficient to suppress the growth of sowthistle, whereas canopy interference from chickpea was insufficient to suppress sowthistle growth. In order to improve the competitive ability of chickpea with sowthistle, either the seeding rate should be increased or the canopy of individual varieties should be manipulated.
Comparing the predatory performance of green lacewing on cotton bollworm on conventional and Bt cotton
We compared the survival of 'Helicoverpa armigera' (Hübner) (Lepidoptera: Noctuidae) eggs and larvae on Bt and conventional cotton, in the presence or absence of the generalist predator, green lacewing larvae, 'Mallada signatus', (Schneider) (Neuroptera: Chrysopidae). In small arenas, green lacewings consumed a similar number of 'H. armigera' eggs (ave. 15.8 ± 1.3 on conventional, 12.6 ± 1.4 on Bt cotton per predator over 24 h) and larvae (ave. 6.8 ± 0.7 conventional, 6.5 ± 0.8 Bt per predator over 24 h) whether on Bt or conventional cotton leaves. Likewise, similar numbers of eggs were consumed by each lacewing larva searching whole plants of either Bt (ave. 15.5 ± 0.6 of 49 over 24 h) or conventional (ave. 13.6 ± 1.1 of 49 over 24 h). On conventional plants over 72 h, survival of 'H. armigera' larvae was 72.8% and decreased to 37.7% when lacewings were present, giving a net consumption rate of 35.1% (8.6 prey per predator over 72 h). On Bt cotton plants, 13.6% of the 'H. armigera' larvae survived after 72 h and this decreased to 1.7% when lacewings were present. This combination of mortality factors operated synergistically. 'Helicoverpa armigera' larvae moved to fruiting structures on conventional or Bt cotton but failed to survive in the squares (young flower buds) when the impacts of Bt and lacewings were combined. The removal of first to second instar 'H. armigera' larvae from squares of Bt cotton by predators has the potential to reduce immediate pest damage and, perhaps more importantly, remove potentially Bt-resistant genotypes.
Weed Management for the Australian Vegetable Industry: Final Report
Weeds are a persistent problem for many vegetable producers in Australia. The common features of vegetable cropping systems, including frequent cultivation, irrigation, and the addition of large quantities of nutritional inputs, mean that the potential for weed growth is high. Weeds have a significant impact on crop profitability, yield and quality, and crop management. In consultation with the Australian industry we sought to identify the most important weed species in Australian vegetable production and the methods currently used to control them, gaps in current knowledge of weed control, potential lessons from other industries, and the most important research, development and extension (RD&E) issues. The project involved a review of the literature, a national survey of vegetable farmers, focus groups and farm visits in major vegetable producing regions across Australia, and key informant interviews. ... The primary output of this project was a series of recommendations for weed control RD&E, to guide future investment.
Interactions of temperature and water potential in displacement of 'Fusarium pseudograminearum' from cereal residues by fungal antagonists
'Fusarium pseudograminearum' (Fp) is a stubble-borne fungus that causes crown rot in wheat and barley. Displacement of 'Fp' from stubble by other fungi was explored. Fungi were isolated from field collections of stubble and identified using morphological and molecular methods. The most abundant species were 'Alternaria' sp., Sterile sp. 1 and 'Fp'. Representative isolates of all species were screened in dual culture with 'Fp' to select candidates for detailed experiments on displacement. 'Trichoderma harzianum (Th), Alternaria infectoria (Ai), Fusarium equiseti (Fe) and Fusarium nygamai (Fn)' were chosen as representing the range of interaction types found. The effects of temperature (5–35 °C) and water potential (-0.3 to -5 MPa) on growth rates, displacement of 'Fp' from infested barley straw and dual culture interaction with Fp were determined. Th was the strongest antagonist overall, but displaced 'Fp' very poorly at the lowest temperatures and water potentials. It was more antagonistic than expected from effects on growth at high temperature and less antagonistic than expected at low temperature. 'Fe' and 'Fn' showed consistent mutual antagonism with 'Fp' on contact in dual culture and gave moderate displacement of 'Fp' from straw, with 'Fe' being the most effective antagonist under cool dry conditions. 'Ai' gave very poor displacement of 'Fp' from straw, despite being the most common straw fungus, confirming that displacement was due to antagonism and not just the presence of other fungi. The type of interaction in dual culture was consistent with degree of displacement from straw and could be used to indicate which environmental conditions were most limiting for an antagonist. The ability to displace 'Fp' under cool dry conditions appears to be critical.
Nutritional constraints on displacement of 'Fusarium pseudograminearum' from cereal straw by antagonists
Displacement of the fungus 'Fusarium pseudograminearum' from stubble by antagonists is a potential means of biocontrol of crown rot in cereals. The role of carbon and nitrogen nutrition in interactions between the pathogen and the antagonists 'Fusarium equiseti', 'Fusarium nygamai', 'Trichoderma harzianum' and the non-antagonistic straw fungus 'Alternaria infectoria' was investigated. Sole carbon source utilization patterns on Biolog plates were similar among the three 'Fusarium' species, suggesting a possible role for competition. However, carbon niche overlap was unlikely to be important in antagonism by 'T. harzianum'. Straw medium supplemented with sugars generally reduced the inhibitory effect of antagonists on growth of 'F. pseudograminearum' in dual culture, indicating that availability of simple carbon sources does not limit antagonism. Adding nitrogen as urea, nitrate or ammonium to straw medium had little effect on antagonism by 'F. equiseti' and 'F. nygamai', but ammonium addition removed the inhibitory effect of 'T. harzianum' on growth of 'F. pseudograminearum'. Displacement of 'F. pseudograminearum' from straw by all fungi in a Petri dish assay was greater when urea or nitrate was used as a nitrogen source than with ammonium. All forms of nitrogen significantly increased displacement of 'F. pseudograminearum' from straw under simulated field conditions when straws were either inoculated with 'T. harzianum' or exposed to resident soil microbes. However, in 2 out of 3 experiments urea and nitrate were more effective than ammonium. The results suggest that availability of nitrogen, but not carbon, is limiting the activities of antagonists of 'F. pseudograminearum' in straw, and the way nitrogen is applied can influence the rate of displacement and mortality of the pathogen in host residues.
Impacts of 'Hyparrhenia hirta' (L.) Stapf (Coolatai grass) on native vegetation in a travelling stock route in northern New South Wales
'Hyparrhenia hirta' (L.) Stapf (Coolatai grass, tambookie grass) is an invasive grass from Africa and the Middle East that has infested large areas of northern New South Wales (NSW) and also occurs in other Australian states. Ten plots were set up for this monitoring study in white box/yellow box/Blakely's red gum woodland, an endangered ecological community, on a travelling stock route near Manilla. Five plots were in an area infested by 'H. hirta' and the rest were in an area where infestations had previously been controlled by spot spraying with glyphosate. Vegetation surveys were conducted in these plots in autumn 2003 and spring 2005. In both surveys 'H. hirta' dominated ground cover in all infested sites and greatly reduced the species richness of native flora, but was absent from the controlled sites. The presence of 'H. hirta' reduced native species richness by about 48% in 20 x 20 m plots and 59% in 6 x 5 m plots in 2003. Results were similar in 2005. Projected cover of 'H. hirta' greatly exceeded that of all native ground-cover species combined in the infested plots. The results are consistent with those of McArdle et al. (2004) from Kwiambal National Park and demonstrate that the impact of this weed on species richness in travelling stock routes, which are intermittently grazed, may be as severe as those in conservation reserves, where domestic livestock grazing is excluded.
Ecological studies of 'Hyparrhenia hirta' (L.) Stapf in northern New South Wales
'Hyparrhenia hirta' (L.) Stapf (Coolatai grass) is a summer active, C4 perennial grass, native to southern Africa and the Mediterranean region. In recent years its range has expanded rapidly and there are now populations of H. hirta in all states and Territories of Australia except Tasmania. It invades native grassy and open woodland communities, including roadsides and travelling stock routes, national parks and pastures. There is little published information on the biology and ecology of 'H. hirta' in the summer rainfall environment of northern New South Wales. This study aimed to increase our understanding of key aspects of the ecophysiology, population dynamics and community ecology of 'H. hirta' to assist in control and management.
Phytotoxic response and yield of chickpea ('Cicer arietinum') genotypes with pre-emergence application of isoxaflutole
Balance® (75% a.i. isoxaflutole) at 100 g/ha is registered in Australia for the control of several broadleaf weeds in chickpea. Polyhouse and field experiments were carried out to examine the tolerance of chickpea genotypes to isoxaflutole. Seven rates of isoxaflutole [0, 18.75, 37.5, 75 (recommended rate), 150, 300 and 600 g a.i./ha] were applied to 20 genotypes in the first polyhouse experiment while in the second experiment, 16 genotypes were tested. In the field, six genotypes were treated with five herbicide rates (0, 37.5, 75, 150 and 300 g a.i./ha). There was a strong dose response in the polyhouse experiments in visual injury ratings, plant height, and shoot and root dry weight. In general, there was less herbicide injury to the kabuli genotypes than in the desi chickpea genotypes. Chickpea genotypes Yorker, Howzat, Amethyst, Gully, 91025-3021, Jimbour, S 95425 and FLIP 94-92C exhibited higher overall mean injury rating in experiment 1. Among these genotypes, shoot dry matter was reduced significantly in Amethyst, Jimbour, 91025-3021 and S 95425. Root dry matter in Amethyst, Jimbour, Yorker, 91025-3021 and S 95425 was also reduced significantly. Height was reduced significantly in all of the above eight genotypes. Although there was less overall injury level in the second polyhouse experiment, which was at lower temperatures, Howzat, Yorker, 91025-3021, FLIP 94-92C and S 95425 again recorded high overall mean injury ratings and should be regarded as more susceptible to isoxaflutole than the other strains. In comparison, 97039-1275 and Kyabra recorded very minor injury symptoms in all the experiments and can be regarded as the most tolerant. The herbicide injury to the genotypes in the field was less than in the polyhouse although Yorker and 91025-3021 showed injury symptoms at early stages of growth. The injury symptoms were temporary and did not produce significant effects on the overall crop growth and yield. It is suggested that plant breeding programs take into account the relative susceptibility of new chickpea genotypes to isoxaflutole.
Effect of night cultivation on the emergence and competition of weeds in buckwheat
The objective of this research project was to identify the effect of night cultivation as a weed management practice to reduce weed populations and their competitive effects within a cropping system. The type of cultivation method used and the degree of soil inversion has been found to alter the number of seeds that are triggered to germinate by a brief exposure to light. For this reason, the project also compared disc tillage and zero tillage systems on potential weed seedling emergence. Buckwheat ('Fagopyrum esculentum' Moench) was chosen as the crop in which to test these effects. The results of the research indicated the potential for short-term reductions in weed seedling emergence when light is excluded during the process of cultivation and sowing. For example, there was a significant reduction in the number of bladder ketmia ('Hibiscus trionum' L.) and amaranth ('Amaranthus' sp.) seedlings that emerged within 24 days following night soil cultivation and sowing. However, this difference was not observed when measured 37 DAS and later. Disc tillage had significantly higher weed densities and biomasses throughout the experiment than the zero-tillage treatments. The buckwheat crop also suppressed weed populations, such that weeding the crop did not increase yield. These results suggest that night cultivation may yet prove beneficial in an integrated weed management system.