Mechanical weed control for integrated and organic salad and brassica production

Summary

Diminishing herbicide options, fear of ground water contamination and customer pressure to minimise herbicide use are all pushing the 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. A major constraint to continued growth of processed bagged salads is contaminants. Major contaminants are weeds and weed seeds, however other pest and disease contaminants are enhanced by poor weed control. The majority of salad crops are hand weeded once and some twice at a cost of £400-£1000/ha depending on weed levels. This task is not liked and leads to back problems. Brassica production is also affected by weed contamination, but to a lesser extent. Better weed control will reduce these problems. It is estimated that only 5% of brassica crops currently require hand weeding, though that is expected to rise after the loss of herbicides such as Cyanazine in 2007. Most organic brassica crops are hand weeded and costs are typically lower at £100 - £250/ha due to wider plant spacing and a greater tolerance to weeds. Typical brassica residual herbicide costs are expensive - between £45 and £60/ha. More cost-effective weed control will have the added commercial benefit of reducing potential reliance on imports of certain produce from outside the UK in the future.
Weeds growing within crop rows continue to be the major problem because of a) gaps in the herbicide control of certain weed species and b) the close proximity of the weeds to the crop making conventional mechanical weeding difficult without risking crop damage. SRI’s imaging and crop row tracking technology has been successfully applied to cultivation equipment for improved inter-row mechanical weed control. There is an opportunity to develop an adaptable, cost-effective technology for mechanically controlling weeds, specifically in-row weeds, for a wide range of brassica and salad crops that would enable machinery to control in-row weeds mechanically. Such a development would increase UK industry competitiveness in a way that is sustainable in a low herbicide environment.
The scientific approach of this Defra sponsored Horticulture LINK project will be to develop a fast, two dimensional mathematical template matching techniques, (exploiting periodicity within the planting grid), which will enable individual crop plants to be located and can cope with crop spacing variability. Regular observations of plant position will be passed to a tracking algorithm that can follow plant location from a moving vehicle. We will need to ensure that this works for a typical range of salad and brassica crop colours, in particular red salad plants. A novel shallow cultivation mechanism will also have to be developed. This will be need to be synchronised with the plant tracking algorithm and will enable weeds to be removed from between crop plants leaving the crop undisturbed. The final phase of the study will allow the performance of the resulting experimental apparatus to be assessed for both physical accuracy and horticultural value in terms of reliability, weed kill and any crop damage.
A number of clear benefits can gained from the project, chiefly environmental benefits resulting from reduced herbicide use as well as lower mechanical weeding costs which would increase potential for organic production. In addition, reducing the number of weeding operations through better targeting may help minimise problems caused by frequent soil disturbance. Other benefits will include improved plant location which may further improve existing inter-row guidance, further reducing herbicide use. The main output of the project will be an experimental prototype demonstrating the technology developed and capable of being taken forward for development by the manufacturing parties.