Papers by Charles N Merfield
Weed Research, 2016
Summary While machines called weeding robots are now commercially available and many more designs... more Summary While machines called weeding robots are now commercially available and many more designs are being actively researched, I contend that current machines are not truly robotic weeders, rather they are essentially self-guiding vehicles carrying weeding tools. I consider true robotic weeders to be a far more difficult objective. While advances in robotics have been outstanding, the weeding component often appears to be an afterthought. I contend that the weeding is as complex as the robotics. A genuine weeding robot should be able to: (i) monitor the crop, weeds, weather and soil, (ii) decide when the crop should be weeded, (iii) choose the optimal weeder, (iv) take the weeder to the field, (v) adjust the weeder for optimal performance, (vi) continuously monitor the entire weeder for blockages and mechanical breakages and fix them in the field, (vii) continuously monitor and adjust the weeder's performance, (viii) return the weeder to the farmyard and (ix) clean, maintain and store the weeder, that is replace all human intervention. This ten-point list both defines and is a guide to what is required for completely autonomous robotic weeding. Currently, this list is far beyond current technology and it may be decades before it is realisable. The aim of this study therefore was not to disparage the achievements of agricultural roboticists, rather it is to highlight the complexity and demands of mechanical weeding and therefore describe what is really required to create a true robotic weeder. I therefore hope it will guide and expedite research and lead to more rapid success for robotic weeding.
Teagasc Organic Production …, 2008
An organic rotation trial was established at Oak Park in 2000. The crop sequence in the seven yea... more An organic rotation trial was established at Oak Park in 2000. The crop sequence in the seven year rotation was: two years grass-clover, winter wheat, potatoes, winter oats, lupins and spring barley. The grass-clover, which supplies nitrogen to the system, also provides vegetation which of late is cut and mixed with cereal straw to produce compost. The compost replaced sheep manure which was available up to 2007. Manure was applied to potato plots prior to cultivation for the period 2002 to 2007 and to barley plots from 2005 to 2007. The average yield of crops over the period of the rotation was: winter wheat 5.9 t/ha, potatoes 32.7 t/ha, winter oats 5.8 t/ha, lupins 2.4 t/ha and spring barley 4.5 t/ha. Triticale, which was grown in one of the plots designated for winter wheat, had an average yield of 7.5 t/ha. Lupins have been unsatisfactory due to uncompetitiveness with weeds and lateness of maturity.
Any discussion of the farm of the future has to be more philosophical than scientific. Science is... more Any discussion of the farm of the future has to be more philosophical than scientific. Science is unequivocal that predicting the outcome of complex systems is impossible, and the days of experts prophesying the future are over. Further, I concur with John Gray, the British political philosopher, that the days of grand utopian visions are over, along with the monolithic philosophies that spawned them. If we are to plot the future, it has to be brick by brick. Therefore, this is not a prediction, but an analysis of the issues that I believe matter for farms in the future.
New Zealand Journal of Crop and Horticultural Science, Mar 29, 2017
This study examined the effects of organically-derived plant growth promoters (PGPs) on vegetativ... more This study examined the effects of organically-derived plant growth promoters (PGPs) on vegetative growth of Pinot noir cuttings under glasshouse conditions for 8 weeks. Solutions of 10 products were applied four times, 2 weeks apart, as a soil drench. In standard potting mix, none of the products caused significant increases in vegetative growth. In low-nutrient potting mix, three products (Synerlogic, Actavize, Just Fish) increased aspects of growth, such as leaf number, shoot length and shoot and root dry weight. These products were relatively high in NPK, and therefore cutting growth was positively correlated to concentrations of NPK in the added solutions. The results imply that addition of PGPs does not by default enhance growth of grape cuttings, and that the mechanism of growth enhancement appears to be simple nutrient provision, rather than by a more complex physiological route involving plant hormones or hormone mimics.
Field trials were conducted on commercial organic farms over three years to study the effects of ... more Field trials were conducted on commercial organic farms over three years to study the effects of post-emergence thermal weeding in onions (Allium cepa). The results demonstrated the potential of both flame and steam weeding for post-emergence use in onions provided the operation was timed carefully. Early post-emergence thermal weeding is more effective because weeds are smaller, but onions should have at least two leaves to withstand the heat. Following a pre-emergence thermal weeding, two post-emergence passes of either a flame or steam weeder at the 3-leaf and 5leaf growth stage of onions gave economical weed control. This strategy gave a significant yield improvement over the control. In experiments where hand weeding was used to remove mid-season weeds, yields were similar, but labour required for hand weeding after thermal weeding, was reduced by up to 80%. Onion bulb size was also significantly greater in plots that had two post-emergence passes of thermal weeding provided one was at the 3-leaf onion growth stage. None of the thermal treatments used increased the incidence of neck rot in onions. The 3-leaf growth stage appears to be a key timing for effective weed control in onions.
New Zealand Plant Protection, Aug 1, 2003
Most weed management research has been based on synthetic chemicals since the introduction of syn... more Most weed management research has been based on synthetic chemicals since the introduction of synthetic herbicides in the 1940s. In organic agriculture, mechanical methods are often used in place of chemicals. The work described here concerns a three-year field programme in which three methods of mechanical weed control were compared. The work took place on the Heinz Wattie's Organic Farm at Lincoln University ("Kowhai Farm"). The experiment took place in each of the four cropped paddocks and comprised a linear randomised complete block design with three treatments and a control replicated five times (20 plots/paddocks). The treatments were tine, spoon and inter-row weeding. The yield of borage seed did not differ significantly between the three treatments. However, for linseed, both spoon and tine weeding improved yield compared with the control. In beans, highest yields were obtained with the spoon weeder and inter-row hoe.
Weed Research, Jul 6, 2016
Summary While machines called weeding robots are now commercially available and many more designs... more Summary While machines called weeding robots are now commercially available and many more designs are being actively researched, I contend that current machines are not truly robotic weeders, rather they are essentially self-guiding vehicles carrying weeding tools. I consider true robotic weeders to be a far more difficult objective. While advances in robotics have been outstanding, the weeding component often appears to be an afterthought. I contend that the weeding is as complex as the robotics. A genuine weeding robot should be able to: (i) monitor the crop, weeds, weather and soil, (ii) decide when the crop should be weeded, (iii) choose the optimal weeder, (iv) take the weeder to the field, (v) adjust the weeder for optimal performance, (vi) continuously monitor the entire weeder for blockages and mechanical breakages and fix them in the field, (vii) continuously monitor and adjust the weeder's performance, (viii) return the weeder to the farmyard and (ix) clean, maintain and store the weeder, that is replace all human intervention. This ten-point list both defines and is a guide to what is required for completely autonomous robotic weeding. Currently, this list is far beyond current technology and it may be decades before it is realisable. The aim of this study therefore was not to disparage the achievements of agricultural roboticists, rather it is to highlight the complexity and demands of mechanical weeding and therefore describe what is really required to create a true robotic weeder. I therefore hope it will guide and expedite research and lead to more rapid success for robotic weeding.
New Zealand Plant Protection, Jan 8, 2014
The tradescantia leaf beetle (Neolema ogloblini) was released in 2011 as a biological control age... more The tradescantia leaf beetle (Neolema ogloblini) was released in 2011 as a biological control agent for tradescantia (Tradescantia fluminensis), one of New Zealand's worst environmental weeds. Tradescantia prevents native forest regeneration by growing over and shading out native seedlings at ground level. To assess N. ogloblini's effectiveness, a glasshouse experiment compared ground level light readings before and after beetle feeding and the response of two native seedlings, kawakawa (Macropiper excelsum) and mahoe (Melicytus ramiflorus). Feeding damage caused light readings to increase above 5% of fulllight, the threshold estimated as necessary for regeneration of native plants by previous research. This resulted in a significant increase in kawakawa seedling height and leaf length. This study suggests that native forest regeneration may benefit from feeding damage to tradescantia caused by N. ogloblini in the field.
An organic rotation trial was established at Oak Park in 2000. The crop sequence in the seven yea... more An organic rotation trial was established at Oak Park in 2000. The crop sequence in the seven year rotation was: two years grass-clover, winter wheat, potatoes, winter oats, lupins and spring barley. The grass-clover, which supplies nitrogen to the system, also provides vegetation which of late is cut and mixed with cereal straw to produce compost. The compost replaced sheep manure which was available up to 2007. Manure was applied to potato plots prior to cultivation for the period 2002 to 2007 and to barley plots from 2005 to 2007. The average yield of crops over the period of the rotation was: winter wheat 5.9 t/ha, potatoes 32.7 t/ha, winter oats 5.8 t/ha, lupins 2.4 t/ha and spring barley 4.5 t/ha. Triticale, which was grown in one of the plots designated for winter wheat, had an average yield of 7.5 t/ha. Lupins have been unsatisfactory due to uncompetitiveness with weeds and lateness of maturity.
Biological Control, 2004
This paper describes field and laboratory time-lapse video analyses of the behavioral responses o... more This paper describes field and laboratory time-lapse video analyses of the behavioral responses of the groups: Arachnida: Acari, Araneae, and Opiliones; Myriapoda: Chilopoda; Hymenoptera: Formicidae; Crustacea: Isopoda; and Coleoptera: Staphylinidae to live eggs of the brown blowfly, Calliphora stygia F. (Diptera: Calliphoridae), used as factitious prey in two contrasting agricultural field margins and in the laboratory. Field video results showed that predation by mites was greatest in tree-lined boundaries while centipede numbers and activity were greater in post-and-wire boundaries. All except Staphylinidae showed clear diurnal patterns of activity and egg predation rate over the 12 h recording period. Based on the number of eggs removed, number of eggs examined, predator numbers, and predator activity, three indices were formulated that allowed predator groups to be ranked according to their effectiveness as predators. Commensal interactions between the mites and harvestmen, mediated via mite-pierced eggs, were suggested from field data and confirmed in the laboratory. Phalangium opilio preferred to feed on both manually and mite-pierced compared with untreated eggs, but showed a stronger preference for manually pierced ones than mite-pierced, consuming six times as many over the same period. This is the first demonstration of a commensal interaction between two agroecosystem predators. If commensalism is common in agroecosystems it could increase the effectiveness of biological control. It may also need to be incorporated within theoretical models and may complicate the extrapolation of laboratory-based feeding studies to field situations.
Weed Research, Aug 14, 2020
Weed management using synthetic herbicides is undergoing a global decline, necessitating a re‐eva... more Weed management using synthetic herbicides is undergoing a global decline, necessitating a re‐evaluation of existing control measures and the development of novel weed management tools. ‘Mini‐ridging’ is a non‐discriminatory, physical weeding method that functions by burying weeds in the intrarow with a laterally shifted ridge of soil. In glasshouse trials using potted plants, we found that plant recovery after soil application was influenced by plant size, which in turn was influenced by plant species, developmental stage and/or age. The likelihood of plant recovery after soil application was negatively related to the depth of soil applied: very few plants survived total coverage by soil but, conversely, survival could be substantial if some parts of the plants were not covered. The results suggest that burial under a depth of 6 cm of soil would eliminate most plants regardless of species or growth stage. Larger plants would require the application of a greater total depth of soil to achieve this 6 cm of soil cover, and weed management would, therefore, tend to be more successful and more practical if weeds were targeted when still small. This research demonstrates the potential of plant burial as a simple and reliable means of non‐chemical weed management, and re‐emphasises that, for weed control to be effective, the applied soil layer must cover the whole plant.
Environmental Science and Pollution Research, Jan 9, 2023
A small proportion of the thousands of pesticides on the market today are associated with a dispr... more A small proportion of the thousands of pesticides on the market today are associated with a disproportionately high incidence of severe acute pesticide poisoning and suicide. Paraquat stands out as one of the most lethal pesticides in common use, frequently involved in fatal incidents due to suicides or accidental exposure. Even though paraquat has been banned in over 67 countries, it is still widely used in many others, particularly in Asia and Latin America. Based on a literature review and consultations, this paper identifies options for replacing paraquat and distils practical lessons from numerous successes around the world. Our aim is to support regulators, policymakers, agronomists and the supply chain sector with practical information related to phasing out paraquat. Production data consistently failed to show any negative effects of banning paraquat on agricultural productivity. A wide range of alternative approaches to weed management and crop defoliation are available, many of which do not rely on herbicides. Over 1.25 million farmers in low-and middle-income countries (LMICs) successfully produce a range of crops for private voluntary standards (PVS) in food and fiber supply chains which prohibit paraquat use. We conclude from the findings of this study that eliminating paraquat will save lives without reducing agricultural productivity. Less hazardous and more sustainable alternatives exist. To enhance successful adoption and uptake of these methods on a wide scale, farmers require training and support within an enabling policy environment.
Grassland research and practice series,, 2010
The hypothesis that by increasing carrot (Daucus carota) plant density the contribution to seed y... more The hypothesis that by increasing carrot (Daucus carota) plant density the contribution to seed yield by the primary umbels would increase, and that therefore both seed yield and seed quality would increase, was examined in two experiments in different years in Canterbury. A radial trial design provided plant densities from 2 to 84 plants/m 2 and from 4 to 100 plants/m 2 in experiments one and two respectively. Seed yield increased with increasing plant density in both experiments, and at the highest density the primary umbels contributed 90% (experiment one) and 60% (experiment two) of the seed yield. In both experiments seeds from the primary umbels had a greater thousand seed weight and higher germination than those from the other order umbels, and for the second experiment they also had higher seed vigour. The quality of seeds from the primary umbels was consistently higher than that of seeds from the secondary umbels across all plant densities, and for the latter, both germination and seed vigour declined as plant density increased. These results therefore support the hypothesis, and densities higher than the 20 plants/m 2 currently used commercially have the potential to increase both seed yield and quality.
In the mid-1990s the organic agriculture movement started a drive for only organically grown seed... more In the mid-1990s the organic agriculture movement started a drive for only organically grown seed to be used in organic agriculture due to its growing commercialisation, the advent of transgenetic crops and to ensure authenticity. „Organic seed‟ is a multi-level concept. At its most simple, it just refers to „certified‟ planting seed produced according to organic standards, then as a proxy for organic cultivars and breeding approaches, and finishing with political and philosophical issues such as food sovereignty. The International Federation of Organic Agricultural Movements (IFOAM) finally adopted a formal position on organic seed in 2011. The drive for organic planting seed in the developed world has mostly been fulfilled through the use of progressive implementation systems whereby the amount of non-organic seed that is permitted is slowly reduced. However, these systems have had some perverse outcomes, at least initially, and the management of their implementation is somewhat h...
Organic markets in New Zealand and overseas are undergoing a major sea change. A couple of years ... more Organic markets in New Zealand and overseas are undergoing a major sea change. A couple of years ago over supply of organic product was unheard of. When it came to selling their goods producers generally had it pretty easy. If the quality was right then there was almost always a ready buyer knocking on the door. Today in Europe there are a number of organic markets where supply now easily exceeds up-front demand. Milk is a good example. In 2001 up to half of the organic milk produced in the UK was sold as conventional. Unsurprisingly there was a sharp drop in organic milk prices of over 10 cents a litre as a result. The same is now happening with organic meat in the UK prompting influential media presenter, columnist and environmental campaigner John Humphreys to examine what he sees as a reversal of the growth of the organic industry in the UK where “organic prices are quietly falling reducing the organic premium and therefore margins for organic producers”. While it is fashionable...
New Zealand Journal of Crop and Horticultural Science, 2015
Tomato potato psyllid (TPP; Bactericera cockerelli) is a serious pest of solanaceous crops in New... more Tomato potato psyllid (TPP; Bactericera cockerelli) is a serious pest of solanaceous crops in New Zealand. Control of TPP is currently dominated by synthetic biocides, although this method is curative and does not always prevent transmission of TPP-vectored plant diseases. This study evaluated mesh crop covers as non-chemical alternatives for controlling TPP in potato crops. Over two growing seasons in Canterbury, New Zealand, potatoes growing under mesh covers were found to have reduced numbers of TPP nymphs and adults, increased tuber size, increased overall yield and enhanced storage potential compared with uncovered plots. There was also a slight reduction in potato blight spores under mesh, and the actual occurrence of blight was slightly reduced in one trial. The results of this study indicate that mesh crop covers could provide a viable option for potato growers who wish to protect their crops from TPP without using chemical insecticides.
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Papers by Charles N Merfield