Abstract

It is now widely recognized that Bidens pilosa has become a problematic broadleaf weed in many ecosystems across the world and, particularly in the light of recent climate change conditions, closer management strategies are required to curtail its impact on agricultural cropping. In this investigation, experiments were conducted to evaluate the effect of environmental factors on the germination and emergence of B. pilosa, and also on the response of this weed to commonly available post-emergence herbicides in Australia. The environmental factors of particular interest to this current work were the effect of light and temperature, salinity, burial depth and moisture on B. pilosa since these are key management issues in Australian agriculture. In addition, the effects of a number of commonly used herbicides were examined, because of concerns regarding emerging herbicide resistance. In the tested light/dark regimes, germination was found to be higher at fluctuating day/night temperatures of 25/15 °C and 30/20 °C (92–93%) than at 35/25 °C (79%), whilst across the different temperature ranges, germination was higher in the light/dark regime (79–93%) than in complete darkness (22–38%). The standard five-minute temperature pretreatment required for 50% inhibition of maximum germination was found to be 160 °C, and it was further shown that no seeds germinated at temperatures higher than 240 °C. With regard to salinity, some B. pilosa seeds germinated (3%) in 200 mM sodium chloride (NaCl) but all failed to germinate at 250 mM NaCl. Germination declined from 89% to 2% as the external osmotic potential decreased from 0 to −0.6 MPa, and germination ceased at −0.8 MPa. Seeding emergence of B. pilosa was maximum (71%) for seeds placed on the soil surface and it was found that no seedlings emerged from a depth of 8 cm or greater. A depth of 3.75 cm was required to inhibit the seeds to 50% of the maximum emergence. In this study, application of glufosinate, glyphosate and paraquat provided commercially acceptable control levels (generally accepted as >90%) when applied at the four-leaf stage of B. pilosa. However, none of the herbicide treatments involved in this study provided this level of control when applied at the six-leaf stage. In summary, B. pilosa germination has been clearly shown to be stimulated by light and thus its emergence was greatest from the soil surface. This suggests that infestation from this weed will remain as a problem in no-till conservation agriculture systems, the use of which is increasing now throughout the world. It is intended that information generated from this study be used to develop more effective integrated management programs for B. pilosa and similar weeds in commercial agricultural environments which are tending toward conservation approaches.

Highlights

  • Aspects of Bidens pilosa germination were evaluated by placing experimental lots of 25 seeds in a 9 cm diameter Petri dish containing two layers of Whatman No.[1] filter paper moistened with either 5 ml of distilled water or a relevant experimental solution

  • The dishes were placed in sealed plastic bags and placed in an incubator at fluctuating day/light temperatures of 30/20 °C in light/dark conditions, unless otherwise indicated

  • The photoperiod in the incubator was set at 12 h light to coincide with the high-temperature period. In this investigation, seed germination was evaluated up to a maximum of 14 days after the start of the experiment, as no seeds germinated in a preliminary control experiment in the incubator after this period

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Summary

Results and Discussion

Effect of temperature and light on germination rate. The role of temperature in the germination of weed species is a complex issue. Notwithstanding the incomplete picture of seed emergence parameters, the greater level of surface germination strongly suggests that no-till or conservation agriculture practices would enhance B. pilosa seedling emergence This is because, in such farming systems, a large fraction of weed seeds dropped by previous infestations remain on or close to the soil surface[17]. With no-till fallow periods, application of the non-selective post-emergence herbicides at or before the four-leaf stage of B. pilosa can significantly reduce its density and prevent reseeding in the following season Knowledge gained from these studies in Australian conditions should be helpful for devising regional control measures in cropping situations and for limiting the future spread of B. pilosa. Results may differ; there is a need to conduct field trials

Material and Methods
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