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Spot sprayer that knows its onions

25 August 2011

Automatically detecting potato volunteers in onion and carrots crops, and spot spraying to avoid crop contamination, was the aim of a recently completed LINK-funded project. Results have indicated up to 95 per cent control, at costs and work rates competitive to existing methods.

Precision farming techniques developed by a Hort LINK project team which included the AHDB Potatoes and HDC as well as expertise from researchers; technology, electronics and machinery companies; the agrochemical industry; and growers that produce pre-pack carrot, onions and potatoes has enabled individual weed detection using innovative technology to allow spot herbicide application.
 The team included: The Arable Group (Spray Applications Unit), Tillett and Hague Technology, Garford Farm Machinery, Robydome Electronics, Micron Sprayers, Hypro EU Ltd, Allium and Brassica Centre, Monsanto, Huntapac Ltd, and the growers F B Parrish and Sons and A Findlay.

 Potato volunteers can seriously impact the yield of carrot and onion crops, restrict lifting, encourage and harbour pests and diseases and cause varietal cross contamination when potatoes are next grown in the rotation.

 As a result of changes to herbicide registration requirements, growers no longer have access to any selective herbicide to control volunteer potatoes in crops of carrots and onions. Manual spot spraying or rouging as alternatives to herbicide application is cost prohibitive on a commercial scale.

 Professor Paul Miller from The Arable Group’s Spray Application Unit at Silsoe said: “Our aim was to effectively target the volunteers, and at the same time minimise the contamination of the crop and any loss of yield.

 “With the legislative onslaught of 91/414/EEC and The Water Framework Directive the group was looking for an alternative approach to the use of selective herbicides, many of which have already been lost, and those that remain may have limited availability in the future. Glyphosate was chosen for the research, as it’s effective, and regarded as a chemical likely to survive pending regulations.”

 A six-metre, front-mounted experimental spray rig was developed for the project, with three cameras (one per bed) and around fifty individual spray nozzles depending on the row spacing of the crop to be treated.

 “The computing system takes images (at 30Hz) from the cameras, identifies weed potatoes and then tracks them until they pass under an array of Alternator nozzles. The computer calculates which nozzles need to be switched on, and for how long, to give an effective dose, whilst minimising crop contamination.”

 The Alternator nozzles were specially designed for the project to produce large drops, which are well suited to targeting weeds, such as volunteer potatoes, with glyphosate without drift.

 “The cameras recognise the size and shape of the potato plants in onion crops, over a wide range of growth stages, including when the crop plants are very small. In carrot crops the volunteers are easily detected between rows but because of top growth the potato volunteer can only be detected when it breaks through the carrot foliage.

 “The rapid formation and collapsing of low drift sprays with an accuracy of +/- 20mm, at forward speeds of up to 5kph is particularly impressive,” added Professor Miller.

 “The field trial results at work rates in excess of 2ha/hr have shown levels of control of between 95 to 75 per cent with a single pass. Therefore this provides a practical option, for the control of volunteer potatoes, now that key selective herbicides have been lost. The approach is also capable of further development should the restrictions on herbicide use continue to get tighter. By spot spraying target weeds it can potentially save 95 per cent herbicide application compared with a blanket operation.”

 A follow-on project will examine the technique in a wider range of crops and will trial a greater range of selective and non-selective herbicides for weed control. The outcomes will be communicated to levy-payers in future issues of Grower Gateway.

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