Advancing splatter gun technology for rangeland weeds

To determine whether more rangeland weeds could be susceptible to low-volume highconcentration herbicide applications (e.g., splatter guns), trials were initiated on gamba grass (Andropogon gayanus), rubber vine (Cryptostegia grandiflora), prickly acacia (Vachellia nilotica), and Chinee apple (Ziziphus mauritiana). For gamba grass, a rate response trial (0, 9, 18, 27, 36, 45 and 54 g a.i./L of mixture) of glyphosate has shown that 100% mortality can be achieved at rates ≥ 36 g a.i./L of mixture. A rubber vine trial is comparing the effect of timing of applications (between December and May) of two herbicides. Six months after treatment (MAT), Grazon™ Extra (triclopyr/picloram/aminopyralid) recorded the highest (i.e. December application) but most variable efficacy (0-80%) compared to 40-70% for Brush-off® (metsulfuron-methyl). The optimum way to spray plants using Hotshot™ (aminopyralid/fluroxypyr) is being investigated in a prickly acacia trial. Preliminary results, six MAT suggest that more severe damage occurs if the amount applied is calculated on the basis of the whole surface area of plants (i.e. both sides), but spraying from one side appears to be sufficient. For Chinee apple, a screening trial of five herbicides and two rates is showing that Brush-off® (metsulfuron-methyl) and Stinger™ (aminopyralid/metsulfuron-methyl) are the best performing herbicides, but only on smaller plants (< 2 m high) and at the highest applied rates 12 MAT. While promising, the variability in results indicates that many factors may affect efficacy, including the health, size and density of plants, herbicide choice and mixture/application rate, presence/absence of biological control agents and climatic conditions

Foliar herbicide control of sticky florestina (Florestina tripteris DC.)

Sticky florestina (Florestina tripteris DC.) is an annual exotic weed that has become naturalised near the townships of Tambo and Barcaldine in central western Queensland, Australia. Three experiments conducted near Barcaldine identified foliar herbicides effective in killing sticky florestina plants and in providing residual activity to reduce recruitment from the soil seed bank. An initial chemical screening experiment evaluated the efficacy of 28 herbicide treatments. The most promising herbicides were then further evaluated in two response-rate experiments. Overall, 2,4-D/picloram, aminopyralid/fluroxypyr, clopyralid, metsulfuron-methyl and triclopyr/picloram proved to be the most effective selective herbicides. Two of these, metsulfuron-methyl at 18 g active ingredient (a.i) ha–1 and 2,4-D + picloram at 900 g a.i. ha–1 + 225 g a.i. ha–1 have now been included in a minor use permit (PER11920) with the Australian Pesticides and Veterinary Medicines Authority (APVMA) for the control of sticky florestina in pasture, stock route, roadside and non-crop situations using both spot and boom-spray applications (APVMA 2010). The permit also allows the use of 2,4-D amine for the control of seedlings only

Herbicide Options to Control Naturalised Infestations of Cereus uruguayanus in Rangeland Environments of Australia

While there are many high profile Opuntioid cactus species invading rangeland environments in Australia, Cereus uruguayanus Ritt. ex Kiesl. has also naturalised and formed large and dense infestations at several locations. With no herbicides registered for control of C. uruguayanus in Australia, the primary aim of this study was to identify effective herbicides to control it using a range of techniques. This involved a large screening trial of twelve herbicides and four techniques, followed by a rate refinement trial for cut stump applications and another to test residual herbicides. Despite most treatments (except monosodium methylarsonate (MSMA)) taking a long time to kill plants, at least one effective herbicide was identified for basal bark (triclopyr/picloram), cut stump (aminopyralid/metsulfuron-methyl, glyphosate, metsulfuron-methyl, triclopyr/picloram, triclopyr/picloram/aminopyralid), stem injection (glyphosate, MSMA, triclopyr/picloram/aminopyralid) and foliar applications (aminopyralid/metsulfuron-methyl, MSMA, triclopyr, triclopyr/picloram/aminopyralid) due to their ability to kill both small and large plants. Ground application of residual herbicides was less conclusive with neither hexazinone nor tebuthiuron causing adequate mortality at the rates applied. This study has identified effective herbicides for the control of C. uruguayanus using several techniques, but further research is needed to refine herbicide rates and develop integrated management strategies for a range of situations and infestation sizes and densities

Foliar herbicide control of sticky florestina (Florestina tripteris DC.)

Sticky florestina (Florestina tripteris DC.) is an annual exotic weed that has become naturalised near the townships of Tambo and Barcaldine in central western Queensland, Australia. Three experiments conducted near Barcaldine identified foliar herbicides effective in killing sticky florestina plants and in providing residual activity to reduce recruitment from the soil seed bank. An initial chemical screening experiment evaluated the efficacy of 28 herbicide treatments. The most promising herbicides were then further evaluated in two response-rate experiments. Overall, 2,4-D/picloram, aminopyralid/fluroxypyr, clopyralid, metsulfuron-methyl and triclopyr/picloram proved to be the most effective selective herbicides. Two of these, metsulfuron-methyl at 18 g active ingredient (a.i) ha–1 and 2,4-D + picloram at 900 g a.i. ha–1 + 225 g a.i. ha–1 have now been included in a minor use permit (PER11920) with the Australian Pesticides and Veterinary Medicines Authority (APVMA) for the control of sticky florestina in pasture, stock route, roadside and non-crop situations using both spot and boom-spray applications (APVMA 2010). The permit also allows the use of 2,4-D amine for the control of seedlings only

Weed leucaena and its significance, implications and control

Leucaena (Leucaena leucocephala) is widely recognized in many countries as a commercially valuable plant, particularly when used as a nutritious fodder in subtropical and tropical regions. However, it is also considered an environmental weed in some countries due to its ability to form dense infestations in disturbed areas, where it is not proactively managed or grazed. These different perspectives have made leucaena a contentious species. Ideally, landholders and relevant jurisdictions in charge of invasive species need to work together to minimize its spread as a weed and manage existing infestations. To date, the response has been varied, ranging from no action through to some jurisdictions formally recognizing leucaena as an environmental weed within relevant legislation and applying requirements to minimize its impact. Between these extremes, there are initiatives such as an industry Code of Practice (i.e. The Leucaena Network in Australia), recommending that those growing leucaena adhere to certain principles and practices to minimize the risk of spread from their operations. The biology of weed leucaena (e.g. large seed production, relatively long-lived seed banks) and the situations in which it spreads (e.g. roadsides and riparian systems) pose management challenges to landholders and relevant jurisdictions. Adaptive management and experimental research are necessary to identify effective control strategies for a range of situations. © 2019, Centro Internacional de Agricultura Tropical (CIAT)

Developing additional herbicide control options for rubber vine (Cryptostegia grandiflora R. Br.)

Herbicide control of rubber vine (Cryptostegia grandiflora R.Br.), a Weed of National Significance in Australia, can be effectively achieved in most situations using a range of chemicals and various techniques, including basal bark, cut stump, foliar and aerial applications. Nevertheless control in areas with poor access and with native vegetation still poses difficulties for some land managers, particularly doing so in a cost effective manner. The successful incorporation of low-volume high-concentration herbicide applications into control programs for several woody weeds in recent years prompted further testing of this technique for control of rubber vine. The efficacy of single rates of four herbicides plus a combination of two herbicides was compared against an untreated control. The herbicide treatments tested contained the active ingredients aminopyralid/ metsulfuron-methyl (375/300 g a.i. kg−1), metsulfuron-methyl (600 g a.i. kg−1), metsulfuronmethyl + glyphosate (600 + 360 g a.i. kg−1), triclopyr/ picloram (300/100 g a.i. kg−1) and triclopyr/picloram/ aminopyralid (200/100/25 g a.i. kg−1). Two years after application, triclopyr/picloram was the only treatment to have given 100% mortality, but statistically it was not significantly different (P >0.05) to aminopyralid/metsulfuron-methyl, metsulfuronmethyl or triclopyr/picloram/aminopyralid, which averaged between 82–91% mortality. The metsulfuronmethyl + glyphosate treatment performed poorly (49% mortality): this appears to be associated with some antagonistic effect given that metsulfuron-methyl on its own performed much better. Based on these results, two more trials have been initiated to refine rates for metsulfuron-methyl and triclopyr/picloram and to compare low-volume high-concentration applications against traditional foliar spraying using the same herbicide (triclopyr/picloram) (in terms of efficacy and cost)

Estimating tropical weed seed longevity with a laboratory test

Longevity of weed seeds in the soil drives the cost and duration of weed control activities. Traditional methods for estimating weed seed longevity, such as repeated field soil sampling and buried packet trials can take many years and substantial resources to complete. A laboratory process, a Controlled Ageing Test (CAT) exposes seeds to an ‘ageing environment’ of 45 oC temperatures and 60% humidity. Data from this test is used to sort species into relatively transient, short lived or long-lived categories of weed seed longevity. This paper reports on examples from a series of trials that seek to correlate the data from CAT batches with longevity data from buried packet trials

The factors influencing weed seed longevity in buried packet trials

Since 2008, a series of trials have studied weed seed longevity by burying packets of seeds in a field research enclosure and retrieving them over time. This paper overviews the results of the completed species where the results have been published by past researchers; Andropogon guyanus, Calotropis procera, Casabella thevetia, Leucaena leucocephala, Stevia ovata, and Ziziphus mauritiana. Completed trials of several species (Azadirachta indica, Lantana camara, Parthenium hysterophorus, Tecoma stans, Prosopis pallida and Vachellia nilotica) are unpublished, but are also summarised. Over 1 to 13 years, seeds of each weed species have been subject to different soil, ground cover and depth treatments. This paper summarises the predominant treatment effects on the seed longevity of each species. Results are presented in terms of a percent (%) reduction in viable weed seed to provide decision makers with relative risk-based information on which to base feasible weed management strategies

The depletion of weed seeds in the soil seed bank

SThe fate of weed seeds in the soil seed bank depends on the processes of emigration, desiccation, predation, and germination. We summarise an ongoing trial on multiple tropical weed species that investigates the emergence of seedlings (successful germination) at a field research site. Intact fruiting structures were placed enclosed in wire mesh cages, on two different soil surfaces and with two different ground covers, and the emergence of seedlings was regularly recorded. By understanding the processes determining the fate of seed, practitioners can plan the duration and timing of control activities. Emergence is still being recorded from most of the seed lots, and the trial demonstrates the persistence that follows a large single reproductive episode