Integration of row widths and chemical and mechanical weed control in winter wheat


Cereals & Oilseeds
Project code:
01 April 1993 - 31 March 1998
AHDB Cereals & Oilseeds.
AHDB sector cost:
£123,722 From HGCA (Project no. 0005/1/92)
Project leader:
J H Orson1, A M Blair2 and J C Caseley3 1Morely Research Centre, Morley, Wymondham, Norfolk NR18 9DB 2ADAS Boxworth, Boxworth, Cambridge CB3 8NN 3IACR Long Ashton, Bristol BS18 9AF



About this project


Mechanical weeding is often viewed as a desirable alternative to chemical weed control and a method of reducing the reliance of modern agricultural systems on pesticides. However, experiments throughout Europe have proven that many passes of the weeders are required resulting in high costs and often reduced yields caused by physical damage to the crop.

This LINK project (funded by MAFF and HGCA) tested the hypothesis that low rates of herbicides would predispose weeds to mechanical damage.

Candidate herbicides were evaluated in the laboratory at IACR Long Ashton for their effect on weeds at rates significantly lower than those recommended on the product label (Section 2 of this report). Measurements were made on the effect of such rates on subsequent growth of weeds. Preference was given to those herbicides which do not appear to present a problem of pesticide movement to water and those which, at low rates, inhibit growth of weeds which were considered more difficult to control mechanically.

The most promising herbicides were then assessed for their ability, at low rates, to predispose weeds to mechanical damage in large containers and eventually in the field (Section 1 of this report). Field experiments were done at ADAS Boxworth, ADAS High Mowthorpe and IACR Long Ashton. It was concluded that for annual broad­ leaved weeds, the application in the spring of 20% of the recommended rate of the appropriate herbicide (according to the weed present) 2-14 days before mechanical weeding provided adequate weed control. A higher rate may be required for cleavers control. The approach did not appear to be sufficiently robust for the control of annual grasses.

The machines used in the experiment were tined finger-weeders. These do not discriminate between crop row and inter-row gaps. It was suggested that widening row spacing would provide more competitive crops within the sown row, reducing weed competition in this area and deflecting the tines of the weeder between the rows. The results suggest that re-arranging crop rows does not improve crop safety or the control achieved by this type of weeder.

Limited experimentation suggested that populations ground beetle numbers recovered more quickly from mechanical weeding than from herbicides. Hence, particularly in areas where there is a need to minimise pesticides, there is an incentive to pursue this type of weed control. The project suggests that winter wheat can be grown in rows wide enough to avoid a significant yield loss and allow image analysis to be exploited to steer an inter-row weeder. This approach, by avoiding crop damage, would allow for a more rigorous physical disturbance of the weeds between the rows while maintaining crop yield. Weed control in the crop row could be achieved by either herbicide seed dressings of the application of herbicide granules at drilling. Such an approach is being researched in a MAFF project which commenced in April 1997.