Volunteer potato control in a range of vegetable crops (2006 - 2009)

Reducing herbicide use in row crops with targeted application methods treating detected weeds in small patches or spots (2010 - 2012)

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Volunteer potato control in a range of vegetable crops (2006 - 2009 )

 Losses resulting from pesticide reviews and customer pressure are reducing selective herbicide options to the point that for some situations there are no products available.  For example, the ’Essential Use’ of post emergence metoxuron (Dosaflo) used to kill potatoes in a wide variety of vegetable crops expired at the end of 2007.  Volunteer potatoes are a particular problem as they are competitive and not very susceptible to mechanical methods.  Furthermore, surviving volunteer potatoes provide a bridge for potato disease, notably blight, which is a concern for potato growers.

In the absence of selective herbicides the targeted application of total herbicides to weed potatoes is an attractive option providing good control with low cost chemicals that have a low environmental impact.  The only available commercial application technique using wipers relies solely on height differential between crop and weed and has important limitations in some circumstances.

 The aim of this initiative was to develop and demonstrate a computer vision based technology that uses weed detection and targeted application of minimal quantities of a total herbicide (e.g. Glyphosate) to control volunteer potatoes in a range of vegetable crops particularly in onions and carrots.

Initial Horticultural Development Council funded work conducted jointly by The Arable Group’s (TAG) spray unit at Silsoe and THT showed great promise and so a follow on Hort Link project was undertaken.  Discrimination between live plant material and background was on the basis of colour as developed in earlier projects.  The discriminators of weed from crop that were investigated included a combination of factors including plant size, shape, height (using optical flow), and position relative to crop rows.  In the final implementation crop height  was not measured as the relatively high steep downward camera view that allowed best determination of the other parameters was not well suited to accurate height measurement by optical flow.

 Spot spraying of individual plants requires novel spray solutions as the required combination of narrow fan angles, low drift and relatively low volumes are rare amongst agricultural spray nozzles.  These factors coupled with the need to form a spray immediately and to stop it without dripping for pulses of down to 30ms duration provide a challenging specification.  The consortium has therefore been evaluating and developing novel nozzle technologies which meet this specification.

Field plot trials in 2008 were conducted in commercial onion and carrot crops.  A single bed width spray boom fitted with spot spray nozzles was fitted to a toolframe tractor equipped with a camera and computing equipment for image processing, target tracking and nozzle control.  Overall results showed promise with a very high proportion (95-75%) of volunteer potatoes being killed, though there was sometimes crop damage in the area immediately around target.  Very low levels of crop loss may be tolerable in commercial situations.

A new experimental spot sprayer spanning three 1.8m beds was developed for the 2009 season.  This was based on a disc steered self levelling front mounted toolframe built by Garford Farm Machinery.  Normally this type of toolframe would be fitted with intra or inter-row cultivation blades, but in this case it was fitted with three spray bars each consisting of a 2m long extruded aluminium section with mounting faces on all four sides.  This allowed mounting brackets, electronic boxes and hoses to be conveniently mounted on the bar whilst allowing unrestricted lateral adjustment of nozzles mounted along the forward face.  Hypro EU Ltd provided "Alternator" nozzles especially designed for this application. These nozzles feature narrow (13°) fan angles and produce droplets well suited to the spot application of glyphosate.  The machine was equipped with three cameras connected to a Core Duo PC that processed images, tracked weeds and interfaced with a network of CAN equipped microcontrollers that controlled toolframe functions such as steering and levelling as well as the on/off control of individual nozzle solenoids.  An additional cab mounted PC provided a user interface and display of live images.

The three bed experimental machine performed well in trials covering several hectares through the 2009 season.  The maximum speed was 5 kph and good control of volunteer potatoes was achieved with low levels of damage that were acceptable to growers. Click on this link to see a 31 second, 4 MB Windows Media File format videoof the experimental spot sprayer in action

Trial crops showing automatically spot treated to the left and untreated to the right (onions above parsnips below)

This project was conducted under the Horticulture Link Programme with Defra and the Chemical Regulation Directorate as co-sponsors. The project was part funded by the Horticultural Development Council and The Potato Council and had the following additional partners: TAG,  Robydome Limited, Garford Farm Machinery , Micron Sprayers, Allium & Brassica Centre, Hypro EU Ltd, Monsanto, Hunterpac Ltd, F B Parrish and Sons, A Findlay.

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EU legislation (e.g. the revision of 91/414 EEC and the Water Framework Directive) is reducing herbicide availability - the limited range of herbicides remaining does not cover the weed spectrum encountered and for some weed species there is, or soon will be, no means of control.  Mechanical weed control is now more widely practised, but there are a number of circumstances when these methods are unsatisfactory – in wet weather, and for control of perennial weeds and species with a strong tap root.  Flame and steam weeding are damaging to invertebrates and consume large amounts of energy.  Hand labour has now become expensive and scarce.  Targeted application of herbicides to weeds that are difficult to control mechanically is an attractive option potentially providing good control with minimum chemical quantities and thus a low cost and environmental impact.

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