THT Current projects

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)

Diminishing herbicide options, fear of ground water contamination and customer pressure to minimise herbicide use are all pushing the horticultural industry away from reliance on herbicides. However, product contamination concerns, much of which relate to weeds, necessitate high levels of weed control and have resulted in increasing use of unsustainable hand weeding.

Weeds growing within crop rows are the major problem because they are missed by conventional inter-row mechanical weeding. THT’s imaging and crop row tracking technology applied to inter-row mechanical cultivators improves the situation by reducing the uncultivated within row band through more accurate guidance than can be achieved manually. However, it is inevitable that some weeds are missed. In this project we have developed an adaptable, cost-effective technology for mechanically controlling in-row weeds for a wide range of brassica and salad crops.

Our scientific approach to the project was to develop a fast, two dimensional mathematical template matching techniques, (exploiting periodicity within the planting grid), enabling individual crop plants with some spacing variability to be located. Regular observations of plant position are passed to a tracking algorithm that can follow plant location from a moving vehicle.

A novel shallow cultivation mechanism was also developed. This is synchronised with the plant tracking algorithm enabling weeds to be removed from between crop plants leaving the crop undisturbed.

The sequence of images above shows an experimental cultivator operating above ground on an artificial crop to demonstrate the principle of operation

An experimental implement was constructed based on a standard front mounted Garford vision guided inter-row steerage hoe. A camera was mounted centrally on the implement looking ahead and down such that the full width of the bed was visible over a length of approximately 2.5m. Each hydraulically driven rotating disc cultivator was attached to a depth wheel unit mounted on the implement so that cultivation depth could be consistently maintained (normally at approximately 20mm). The experimental implement had the capacity to take up to five rotating disc units.

Results showed that the machine was effective at removing weeds within the row without removing crop plants. A field trial has shown that a single pass of the machine incorporating intra and inter-row cultivation removes 80% of weeds.

Untreated area (to left) and treated area (to right) two weeks after treatment showing effectiveness

This project was sponsored by Defra under the Horticulture Link Programme and was conducted jointly with Warwick HRI who provided the weed science and agronomy expertise. The project was part funded by the Horticultural Development Council and had the following additional industrial partners: Robydome Limited, Garford Farm Machinery , Edwards Brothers, Robert Montgomery Limited, Allium & Brassica Centre , AGCO

Four commercial within-row weeding machines based on this technology were sold to UK growers by Garfords at the start of the 2008 season. More information on the commercial machines is available on the Robocrop Vision Guidance page. Click on this link to see a 25 second, 6 MB Windows Media File format video a commercial within-row weeding machine in action

Intelligent thinning for direct drilled salads and vegetables using machine vision (2007 - )

Due to field variability in the process of drilling and germinating seed some high value row crops are sown at a higher density (typically x3) than that which is ultimately desired, and then post emergence, mechanically thinned to the required stand. The selective thinning process has the objective of leaving the healthiest plants at as close as possible to the optimum spacing. The intelligence required to make this selection coupled with the accurate mechanical control required has ensured that this process is almost always conducted manually using hand hoes. There is worldwide interest in reducing difficult repetitive field work due to labour availability, cost and health concerns.

The aim of this project is to develop an intelligent thinning technology that uses an ability to look ahead and automatically make selection decisions to maximise crop quality and yield. The project is utilising much of the technology developed in the within row weeding project described above. Unwanted plants are removed using a selective thinning disc similar to that used for removing weeds between transplanted crops. The innovation specific to the thinning application lies mainly in detecting the very small closely spaced seedlings and developing algorithms to automatically decide which plants to remove and which to keep. There are also mechanical challenges relating to the variability in plant spacing that occurs through this process.

Thinning disk in action removing unwanted lettuce plants

Results from initial experimental work funded by the Douglas Bomford Trust in 2007 were encouraging and so we have continued development.. That follow on work has included field testing in California with the assistance of Robocrop importer Solex Corporation Thinning software has been loaded onto two within-row weeders and tested in lettuce grown on 38" and 80" bed configurations. The photograph below show the effect of running the automatic thinner on lettuce drilled at a nominal 3.5" spacing set to produce a stand at 11.5". The area to the left is unthinned and the area to the right has been thinned. The final spacing is generally regarded as at least as good as that achieved manually, though the machine sometimes has difficulty removing plants ("doubles") that have grown closer (<2.5") to each other than intended. This problem would not occur often with a well set up drill, though it is accepted that drilling sometimes has to be conducted under less than ideal conditions and so work is continuing to improve performance in this respect.

A 22 second, 5 MB Windows Media File format video of automatic thinners being trialled on commercial lettuce crops in California can be viewed by clicking here.