Harvest weed seed control: is there a role in northern region farming systems?

Harvest weed seed control (HWSC) is a new approach which targets weed seed removal and/or destruction during the crop harvest operation. The success of HWSC is dependant upon weed seed retention at harvest. To identify and define the potential value of HWSC in northern farming systems, we conducted a field survey. In total 1400 transects across 70 paddocks assessed weed distribution, density and seed production at harvest time in wheat, chickpea and sorghum crops. Seventy weed species were identified, of which many had large seed numbers retained at crop harvest. The most prevalent included common sowthistle, flaxleaf fleabane, awnless barnyard grass, wild oat, and African turnip weed. Our field survey has shown there is a role for HWSC in the northern farming system. Therefore the efficacy of specific HWSC systems on problematic weeds should be evaluated in the northern region

An Evaluation of Growth Characteristics of Faba Bean Cultivars

Resistance to herbicides and the lack of new herbicide options have led researchers to explore alternate methods to manage weed populations in large-scale cropping systems. Crop competition is an effective weed management approach that can reduce the pressure on herbicides. Faba bean (Vicia faba L.) is an important winter legume crop in Australia. Crop traits such as, height, biomass, growth rate, tillering capacity, leaf area, and root growth have been suggested as indicators of the competitive ability of crops against weeds. Based on pot studies at Narrabri and Toowoomba, we assessed the growth traits (biomass, height, leaf area, relative growth rate, and branch number) of six faba bean cultivars and ranked them for their potential ability to compete with weeds. PBA Marne and PBA Zahra were identified as highly competitive faba bean cultivars based on their higher overall ranking score achieved at both locations. PBA Nasma and PBA Samira were ranked highly and moderately competitive at Narrabri and Toowoomba sites, respectively. At Narrabri, PBA Nanu was ranked poorly competitive based on its lower biomass, height, and leaf area than the other cultivars. The weed suppressive ability of these cultivars needs to be assessed in the presence of weeds under field conditions

Emergence of Sonchus oleraceus (common sowthistle) is favoured under zero tillage farming systems

The impact of different tillage treatments and seed burial depth on the emergence of S. oleraceus was evaluated in two fi eld trials. Increasing soil disturbance reduced S. oleraceus emergence and buried a greater proportion of seed below 2 cm than zero tillage or single operation tillage treatments. S. oleraceus seed emergence was greatest from depths of 0 and 1 cm, however a small amount emerged from a depth of 2 cm while no seedlings emerged from 5 and 10 cm depths. This study highlights that S. oleraceus emergence is favoured in zero tillage systems and that burial of seed through tillage below 2 cm will inhibit emergence of this weed

Response of wild oats to environmental stresses

Take home message • When under heat and water stress, wild oat plants can mature 3 weeks earlier than non-stressed plants • Stressed plants produce 30% fewer seeds; additionally, these seeds are 40% smaller and show less dormancy than seeds from non-stressed plants • Seed dormancy can differ between biotypes and between the two types of seeds (primary and secondary) produced by wild oat plants • Early plant maturation can cause early seed shedding depending on the severity of heat and water stress • If the occurrence of late season environmental stresses becomes more frequent as forecast under a changing climate, the efficacy of strategies such as harvest weed seed control may further diminish for wild oats

Impact of Soil Water Stress at Seed Development Stage on Phenology, Fecundity and Seed Dormancy of Avena sterilis ssp. ludoviciana

Wild oat (Avena sterilis ssp. ludoviciana (Durieu) Nyman) is considered the most difficult-to-control winter weed in the northern grain region (NGR) of Australia particularly following the adoption of no-till conservation agriculture and the enhanced reliance on herbicides for weed control. A diversity of survival mechanisms is responsible for its persistence in no-till conservation cropping. Among them long-term, variable seed dormancy is the most important. A number of environmental stresses (for example drought) are known to affect the seed dormancy status. We hypothesized that the increasing frequency of hot and dry period in late winter/early spring season in the NGR might help to mature and shed less dormant wild oat seeds before the wheat crop is harvested. This early shedding of highly germinable seed better aids persistence in no-till conservation cropping systems. Our research showed that soil water stress applied at seed development stage resulted in lower number (16–22% less) of early maturing (5–20 days earlier) less dormant (28% less) seeds compared with control plants. This observation was made for a number of biotypes either coming from within one location or between locations within the NGR. Thus, the frequent hot and dry period at the time of seed development in the NGR is responsible for production of less dormant Avena sterilis ssp. ludoviciana seeds where no-till conservation cropping is helping to retain these seeds on the top soil. Under favourable germination conditions in the following season these less dormant seeds will immediately be available to re-infest the autumn/winter-sown wheat crop

Crop competition effects on weeds and crops

Take home message • There is convincing evidence that increased crop competition in sorghum, mungbean, faba bean and chickpea resulting from narrower row spacing and/or increased crop density reduces growth and seed production of feathertop Rhodes grass and sowthistle • Importantly, in most instances, narrower row spacing and increased plant density did not have a negative impact on grain yield. In situations where resources (e.g. water) were not limiting, more competitive crops resulted in higher yield • In general, when there is low yield potential (usually due to limited resources) growing a crop at a narrow row spacing or increased crop density is more likely to result in yield loss. In contrast, when there is a high yield potential, crops grown at wide row spacing are likely to result in yield loss when compared to narrow row spacing

Imazapic and diuron availability and toxicity in different soils

Take home message • Herbicide residue levels can be measured in soil, but to interpret what soil analysis results mean for the subsequent crop, information about crop toxicity thresholds, and soil-specific herbicide availability is needed. • An approach has been developed to derive toxicity thresholds and predict herbicide availability in different soils to provide a prediction of safety for cropping. • Soil analysis for herbicide residues is not a replacement for using herbicides according to label requirements. • Additional ground truthing of this proof-of-concept research across a wider range of soil types and environments will strengthen the predictions

Herbicide resistance survey results of the Northern cropping region

Take home message • Glyphosate resistant weeds are present in the northern region. Glyphosate failed to control all of the fleabane populations tested. Glyphosate resistance was also prevalent in feathertop Rhodes grass, windmill grass and awnless barnyard grass, with resistance detected in 68%, 58% and 36% of populations, respectively. Only 14% of sowthistle populations were resistant to glyphosate • Evolved herbicide resistance to haloxyfop was also detected in feathertop Rhodes grass, albeit at a low frequency • Other herbicides such as 2,4-D amine, propaquizafop and clethodim provided good control of the broadleaf and grass weeds tested • Farmers and agronomists should incorporate non-chemical weed management tactics to ensure sustainability of current herbicides • These survey results provide a first glimpse into the state of herbicide resistance in key crop weeds for Queensland and the Northern region

Growing competitive sorghum and mungbean crops to suppress summer weeds

Take home message • Feathertop Rhodes grass (FTR) and awnless barnyard grass (ABG) are both difficult to control summer grass weeds with both species prone to herbicide resistance evolution • Growing a competitive sorghum or mungbean crop can reduce growth and seed production of FTR and ABG • ABG is more susceptible to the impacts of crop competition than FTR • Sorghum competitiveness can be increased by growing the crop at a narrow row spacing (50 cm) and increased density (10 to 15 plants/m2) • Mungbean competitiveness is most effectively increased through the use of narrow row spacing (25 and 50 cm) • Consider growing a competitive summer crop to take pressure off relying solely on in-crop herbicides for summer grass control

Germination behaviour of Avena sterilis subsp. ludoviciana under a range of light and temperature regimes

Context: Avena sterilis subsp. ludoviciana (wild oats) is one of the major winter weeds of the Northern Grains Region of Australia. The abundance of this weed increased dramatically after the adoption of no-tillage conservation agriculture (NTCA). However, information is lacking on the germination characteristics of the two types of seed (i.e. primary and secondary) that it produces.Aims: We aimed to determine the light and temperature requirements for germination and the time to germination of primary and secondary seeds of A. ludoviciana, in order to find ways to manage this weed effectively under NTCA systems.Methods: Primary and secondary seeds and caryopses from two southern and two northern biotypes were exposed to a range of temperature and light regimes in the glasshouse, and germination was assessed.Key results: All biotypes had ∼25% higher germination from primary than secondary seeds. Removing the hull increased caryopsis germination by ∼70%. The use of a light/dark photoperiod stimulated germination of both types of seed and caryopses compared with continuous darkness. Based on data for caryopses, 7°C and 9°C were found to be optimal germination temperatures for southern and northern biotypes, respectively. At optimum germination temperature, primary caryopses germinated 7–20 days earlier than secondary caryopses. In addition, a light/dark environment resulted in germination 2–6 days earlier than continuous darkness.Conclusions: In the Northern Grains Region, seeds retained on or close to the soil surface (i.e. in NTCA systems) can undergo maximum germination during May–June (late autumn–winter), when long-term average temperatures match optimum germination temperatures. This coincides with winter crop plantings.Implications: The seasonal timing of germination and the difference in germination timing between primary and secondary seeds, which help to stagger emergence of this weed, are major issues that need to be addressed in NTCA systems