Nutrient uptake in tropical turfgrasses growing in winter in southern Queensland

The effects of fertilisers on 8 tropical turfgrasses growing in 100-L bags of sand were studied over winter in Murrumba Downs, just north of Brisbane in southern Queensland (latitude 27.4°S, longitude 153.1°E). The species used were: Axonopus compressus (broad-leaf carpetgrass), Cynodon dactylon (bermudagrass 'Winter Green') and C. dactylon x C. transvaalensis hybrid ('Tifgreen'), Digitaria didactyla (Queensland blue couch), Paspalum notatum (bahiagrass '38824'), Stenotaphrum secundatum (buffalograss 'Palmetto'), Eremochloa ophiuroides (centipedegrass 'Centec') and Zoysia japonica (zoysiagrass 'ZT-11'). Control plots were fertilised with complete fertilisers every month from May to September (72 kg N/ha, 31 kg P/ha, 84 kg K/ha, 48 kg S/ha, 30 kg Ca/ha and 7.2 kg Mg/ha), and unfertilised plots received no fertiliser. Carpetgrass and standard bermudagrass were the most sensitive species to nutrient supply, with lower shoot dry weights in the unfertilised plots (shoots mowed to thatch level) compared with the fertilised plots in June. There were lower shoot dry weights in the unfertilised plots in July for all species, except for buffalograss, centipedegrass and zoysiagrass, and lower shoot dry weights in the unfertilised plots in August for all species, except for centipedegrass. At the end of the experiment in September, unfertilised plots were 11% of the shoot dry weights of fertilised plots, with all species affected. Mean shoot nitrogen concentrations fell from 3.2 to 1.7% in the unfertilised plots from May to August, below the sufficiency range for turfgrasses (2.8-3.5%). There were also declines in P (0.45-0.36%), K (2.4-1.5%), S (0.35-0.25%), Mg (0.24-0.18%) and B (9-6 mg/kg), which were all in the sufficiency range. The shoots in the control plots took up the following levels (kg/ha.month) of nutrients: N, 10.0-27.0; P, 1.6-4.0; K, 8.2-19.8; S, 1.0-4.2; Ca, 1.1-3.3; and Mg, 0.8-2.2, compared with applications (kg/ha.month) of: N, 72; P, 31; K, 84; S, 48; Ca, 30; and Mg, 7.2, indicating a recovery of 14-38% for N, 5-13% for P, 10-24% for K, 2-9% for S, 4-11% for Ca and 11-30% for Mg. These results suggest that buffalograss, centipedegrass and zoysiagrass are less sensitive to low nutrient supply than carpetgrass, bermudagrass, blue couch and bahiagrass. Data on nutrient uptake showed that the less sensitive species required only half or less of the nitrogen required to maintain the growth of the other grasses, indicating potential savings for turf managers in fertiliser costs and the environment in terms of nutrients entering waterways.

Sulfur-associated polioencephalomalacia in cattle grazing plants in the Family Brassicaceae

Polioencephalomalacia was diagnosed histologically in cattle from two herds on the Darling Downs, Queensland, during July-August 2007. In the first incident, 8 of 20 18-month-old Aberdeen Angus steers died while grazing pastures comprising 60% Sisymbrium irio (London rocket) and 40% Capsella bursapastoris (shepherd's purse). In the second incident, 2 of 150 mixed-breed adult cattle died, and another was successfully treated with thiamine, while grazing a pasture comprising almost 100% Raphanus raphanistrum (wild radish). Affected cattle were either found dead or comatose or were seen apparently blind and head-pressing in some cases. For both incidents, plant and water assays were used to calculate the total dietary sulfur content in dry matter as 0.62% and 1.01% respectively, both exceeding the recommended 0.5% for cattle eating more than 40% forage. Blood and tissue assays for lead were negative in both cases. No access to thiaminase, concentrated sodium ion or extrinsic hydrogen sulfide sources were identified in either incident. Below-median late summer and autumn rainfall followed by above-median unseasonal winter rainfall promoted weed growth at the expense of wholesome pasture species before these incidents.

Recruitment and loss of juvenile stages of Helicoverpa spp. (Lepidoptera: Noctuidae) on contaminant plants in chickpea crops

The hypothesis that contaminant plants growing amongst chickpea serve as Helicoverpa sinks by diverting oviposition pressure away from the main crop was tested under field conditions. Gain (recruitment) and loss (presumed mortality) of juvenile stages of Helicoverpa spp. on contaminant faba bean and wheat plants growing in chickpea plots were quantified on a daily basis over a 12-d period. The possibility of posteclosion movement of larvae from the contaminants to the surrounding chickpea crop was examined. Estimated total loss of the census population varied from 80 to 84% across plots and rows. The loss of brown eggs (40–47%) contributed most to the overall loss estimate, followed by loss of white eggs (27–35%) and larvae (6–9%). The cumulative number of individuals entering the white and brown egg and larval stages over the census period ranged from 15 to 58, 10–48 and 1–6 per m row, respectively. The corresponding estimates of mean stage-specific loss, expressed as a percentage of individuals entering the stage, ranged from 52 to 57% for white eggs, 87–108% for brown eggs and 71–87% for first-instar larvae. Mean larval density on chickpea plants in close proximity to the contaminant plants did not exceed the baseline larval density on chickpea further away from the contaminants across rows and plots. The results support the hypothesis that contaminant plants in chickpea plots serve as Helicoverpa sinks by diverting egg pressure from the main crop and elevating mortality of juvenile stages. Deliberate contamination of chickpea crops with other plant species merits further investigation as a cultural pest management strategy for Helicoverpa spp.

The role of fruit traits of bird-dispersed plants in invasiveness and weed risk assessment

Aim: Birds play a major role in the dispersal of seeds of many fleshy-fruited invasive plants. The fruits that birds choose to consume are influenced by fruit traits. However, little is known of how the traits of invasive plant fruits contribute to invasiveness or to their use by frugivores. We aim to gain a greater understanding of these relationships to improve invasive plant management. Location: South-east Queensland, Australia. Methods: We measure a variety of fruit morphology, pulp nutrient and phenology traits of a suite of bird-dispersed alien plants. Frugivore richness of these aliens was derived from the literature. Using regressions and multivariate methods, we investigate relationships between fruit traits, frugivore richness and invasiveness. Results: Plant invasiveness was negatively correlated to fruit size, and all highly invasive species had quite similar fruit morphology [smaller fruits, seeds of intermediate size and few (<10) seeds per fruit]. Lower pulp water was the only pulp nutrient trait associated with invasiveness. There were strong positive relationships between the diversity of bird frugivores and plant invasiveness, and in the diversity of bird frugivores in the study region and another part of the plants' alien range. Main conclusions: Our results suggest that weed risk assessments (WRA) and predictions of invasive success for bird-dispersed plants can be improved. Scoring criteria for WRA regarding fruit size would need to be system-specific, depending on the fruit-processing capabilities of local frugivores. Frugivore richness could be quantified in the plant's natural range, its invasive range elsewhere, or predictions made based on functionally similar fruits.

Effect of Time of Planting and Plant Size on the Productivity of ‘Festival’ and ‘Florida Fortuna’ Strawberry Plants in a Subtropical Environment

The effect of time of planting and plant size on the performance of ‘Festival’ and ‘Florida Fortuna’ strawberry (Fragaria ×ananassa) plants was studied at Nambour in southeastern Queensland, Australia, over 2 years. The main objective of the work was to determine whether small plants yielded proportionally less than large plants as planting was delayed. First, bare-rooted transplants of ‘Festival’ were divided into small (crown diameters ranging from 6 to 10 mm) or large plants (10 to 17 mm) and planted in late March, mid-April, or late April. Second, transplants of ‘Florida Fortuna’ were divided into small (5 to 8 mm) or large plants (8 to 17 mm) and planted in early April, mid-April, or early May. The early planting for each cultivar corresponded with the time that the transplants are first available from commercial strawberry nurseries. Yields were generally greater in plants planted in late March/early April compared with plants planted later. Differences in yield between the small and large plants were consistent across the different times of planting, with the small plants always having lower yields. Small transplants are an issue for the productivity of strawberry fields in this environment whether they are planted early or late. Producers should consider paying a premium for large transplants delivered early in the season.

Protected cropping of strawberry plants in subtropical Queensland

The effect of protected cropping on the performance of two strawberry cultivars ('Festival' and 'Rubygem') and two breeding lines (Breeding Lines 1 and 2) was studied in subtropical Queensland, Australia over two years. Production in this area is affected by rain, with direct damage to the fruit and the development of fruit diseases before harvest. The main objective of the study was to determine whether plants grown under high plastic tunnels had less rain damage, less disease incidence, and higher yields than plants grown outdoors. Our studies show that marketable yields were up to 40% higher in the plants under the tunnels compared with yields of the plants outdoors. This was mainly because fruit from the plants grown under the tunnels had lower incidences of rain damage and/or grey mould. There were no consistent differences in the relative numbers of small and/or misshaped fruit in the two growing environments. This research highlights the potential of protected cropping for strawberry producers in subtropical areas that receive significant rainfall during the growing season.

Role of Diadegma semiclausum (Hymenoptera: Ichneumonidae) in controlling Plutella xylostella (Lepidoptera: Plutellidae): Cage exclusion experiments and direct observation

We evaluated the role of the larval parasitoid, Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae), in controlling Plutella xylostella (L.) (Lepidoptera: Plutellidae) by cage exclusion experiments and direct field observation during the winter season in southern Queensland, Australia. The cage exclusion experiment involved uncaged, open cage and closed cage treatments. A higher percentage (54-83%) of P. xylostella larvae on sentinel plants were lost in the uncaged treatment than the closed (4-9%) or open cage treatments (11-29%). Of the larvae that remained in the uncaged treatment, 72-94% were parasitized by D. semiclausum, much higher than that in the open cage treatment (8-37% in first trial, and 38-63% in second trial). Direct observations showed a significant aggregation response of the field D. semiclausum populations to high host density plants in an experimental plot and to high host density plots that were artificially set-up near to the parasitoid source fields. The degree of aggregation varied in response to habitat quality of the parasitoid source field and scales of the manipulated host patches. As a result, density-dependence in the pattern of parasitism may depend on the relative degree of aggregation of the parasitoid population at a particular scale. A high degree of aggregation seems to be necessary to generate density-dependent parasitism by D. semiclausum. Integration of the cage exclusion experiment and direct observation demonstrated the active and dominant role of this parasitoid in controlling P. xylostella in the winter season. A biologically based IPM strategy, which incorporates the use of D. semiclausum with Bt, is suggested for the management of P. xylostella in seasons or regions with a mild temperature.

Weed species richness, density and relative abundance on farms in the subtropical grain region of Australia

Weed management is one of the most important economic and agronomic issues facing farmers in Australia's grain regions. Weed species occurrence and abundance was monitored between 1997 and 2000 on 46 paddocks (sites) across 18 commercial farms located in the Northern Grain Region. The sites generally fell within 4 disjunct regions, from south to north: Liverpool Plains, Moree, Goondiwindi and Kingaroy. While high species richness was found (139 species or species groups), only 8 species occurred in all 4 regions and many (56 species) only occurred at 1 site or region. No species were observed at every site but 7 species (Sonchus spp., Avena spp., Conyza spp., Echinochloa spp., Convolvulus erubescens, Phalaris spp. and Lactuca serriola) were recorded on more than 70% of sites. The average number of species observed within crops after treatment and before harvest was less than 13. Species richness tended to be higher in winter pulse crops, cotton and in fallows, but overall was similar at the different sampling seasons (summer v. winter). Separate species assemblages associated with the Goondiwindi and Kingaroy regions were identified by correspondence analysis but these appeared to form no logical functional group. The species richness and density was generally low, demonstrating that farmers are managing weed populations effectively in both summer and winter cropping phases. Despite the apparent adoption of conservation tillage, an increase in opportunity cropping and the diversity of crops grown (13) there was no obvious effect of management practices on weed species richness or relative abundance. Avena spp. and Sonchus spp. were 2 of the most dominant weeds, particularly in central and southern latitudes of the region; Amaranthus spp. and Raphanus raphanistrum were the most abundant species in the northern part of the region. The ubiquity of these and other species shows that continued vigilance is required to suppress weeds as a management issue.

The chemical control of the environmental weed basket asparagus (Asparagus aethiopicus L. cv. Sprengeri) in Queensland

A replicated trial to determine effective chemical control methods for the invasive species, basket asparagus (Asparagus aethiopicus L. cv. Sprengeri) was conducted at Currumbin Hill, Queensland, from June 1999 to August 2000. Four herbicides (metsulfuron-methyl, dicamba, glyphosate and diesel) were applied at different times of the year (winter, spring, summer and autumn). Neat diesel applied to adult crowns effectively killed basket asparagus. However, germination of basket asparagus and other weeds was not prevented. An overall spray of 0.06 g metsulfuron-methyl (0.1 g Brush-Off®) + 1 mL BS 1000® L-1 water gave slower but more selective long-term control of basket asparagus when compared to diesel, especially when applied in winter and spring. High rates of foliar applied dicamba were most effective in spring and glyphosate splatter gunned on base of stems in autumn. The combination of increased selectivity, ease of application and likelihood of reduced environmental impacts on native plants, other than coast she-oak (Casuarina equisetifolia L. var. incana Benth.), of metsulfuron-methyl makes it more suitable for controlling large infestations of basket asparagus.

An evaluation of containerized plants for strawberries growing in a subtropical environment.

The productivity of containerized and bare-rooted plants of strawberry (Fragaria * ananassa) was investigated over 4 years in southeastern Queensland, Australia. In the first experiment, plants in small, 75-cm3 cells were compared with bare-rooted plants of 'Festival' and 'Sugarbaby'. A similar experiment was conducted in year 2 with these two cultivars, plus 'Rubygem'. In year 3, plants in large, 125-cm3 cells were compared with small and large bare-rooted plants of 'Festival' and 'Rubygem'. Treatments in each of these experiments were planted on the same date. In the final experiment, plants in large cells and bare-rooted plants of 'Festival' were planted in late March, early April, mid-April, or early May. The plants grown in small cells produced 60% to 85% of the yields of the bare-rooted plants, whereas the yield of plants in large cells was equal to that of the bare-rooted plants. Containerized plants are twice as expensive as bare-rooted plants (A$0.60 vs. A$0.32) (A$=Australian dollar), and gave only similar or lower returns than the bare-rooted plants (A$0.54 to A$3.73 vs. A$1.40 to A$4.09). It can be concluded that containerized strawberry plants are not economically viable in subtropical Queensland under the current price structure and growing system. There was a strong relationship between yield and average plant dry weight (leaves, crowns, and roots) in 'Festival' in the last three experiments, where harvesting continued to late September or early October. Productivity increased by about 18 g for each gram increase in plant dry weight, indicating the dependence of fruit production on vegetative growth in this environment.

Managing the grass-legume balance in Stylosanthes scabra cv. Seca pastures in central Queensland

The impacts of 4 grazing strategies (year-long grazing, summer grazing, winter grazing and winter grazing plus spring burning) on the grass:legume balance were studied between 2000 and 2006 in a pasture oversown with Stylosanthes scabra cv. Seca (Seca stylo) in central Queensland. Seasonal rainfall throughout the study was generally below average. Total pasture yields in autumn were higher in the 2 winter grazing than the 2 summer grazing treatments, largely reflecting the sampling time relative to when grazing occurred. There were few differences in Seca composition in autumn, although there was a clear trend for Seca composition to be reduced by winter grazing plus burning. Both the frequency of occurrence and plant density of Seca were higher under the 2 summer grazing treatments and there was also a trend for the density of juvenile plants (<5 cm height) to be higher in the 2 summer grazing treatments. Seca soil seed banks were generally low and were reduced in the winter grazing plus burning treatment in spring 2002. The frequency of the palatable perennial grass Pennisetum ciliaris (Biloela buffel grass) was reduced while that of the 'increaser' species Bothriochloa pertusa (Indian couch grass) and Stachytarpheta jamaicensis (snake weed) increased in the 2 summer grazing treatments compared with the 2 winter grazing treatments. Burning in spring increased soil loss in treatments grazed in winter. Differences in Seca frequency and density but not composition were explained by the 2 summer grazing treatments promoting 'gaps' in the pasture which were then colonised by Seca plants and other 'increaser' species. It was reasoned that, with time, mature Seca plants in the 2 winter grazing treatments would die so that Seca composition would eventually become higher under summer grazing regimes than under winter grazing. It was concluded that limiting grazing to particular seasons can alter legume:grass balance and that a time-frame of 5-8 years with average to good rainfall would be necessary to achieve large shifts in composition.