Organic wheat survey (OF0107)

Summary

A four year study to monitor fourteen organic farms for weed incidence throughout England and Wales began in summer 1993. Two farms were selected from each of the ‘former ADAS’ regions these being; East, Midlands and West, North, South East (Reading), South East (Wye), South West (Bristol) and South West (Starcross). Each pair of farms had been using organic production for different periods of time. On each farm, five fields were selected at random and assessed for weed incidence and severity in December, March, May and July. If a field was in wheat, a sample of fifty tillers was collected at random at GS 75 (July) from a diagonal traverse. Samples were assessed for severity of all foliar, stem-base and ear diseases. Details of cultivations, sowing date and crop husbandry practices were taken for each field. Soil samples were taken in March 1994 and assessed for pH, organic matter, and nutrient status.
The mean number of fields assessed at each assessment date was 58, the differences in numbers assessed was due to lack of crop in the field or the field being grazed by animals. Over all farms the most frequently occurring weed was Stellaria media (64% of fields) then poa annua (49%), veronica persica, matricaria spp., and rumex spp. in approximately 30% of fields. Elymus repens, polygonum persicaria, avena fatua, avena sativa and triticum aestivum were the least frequently occurring weeds, occurring in under 10% of fields.
Farms were divided into those converted to organic farming pre-1985 and those converted post-1985, this gave approximately 50% of the total farms surveyed in each category. In fields converted to organic farming pre-1985 there was a greater weed incidence overall. Stellaria media was still the most frequently occurring weed but was present in 81% of fields converted pre-1985 and only 59% of fields converted after this date. Actual weed populations were greater in fields converted to organic cropping pre-1985. Papaver rhoeas, stellaria media and matricaria spp. had higher populations in fields converted pre-1985 but alopecurus myosuroides had higher populations in fields converted post this date. Soil type and rotation type had very little effect on weed incidence. The main findings of the work were; the spectrum the most common weeds of organic crops was very similar to that of conventional crops; long periods of organic farming has lead to the build up of specific weeds and the demise of others; weed levels in organic situations were high enough to significantly contribute to economic yield losses in crops; the survey was not large enough to form a complete picture of weeds in organic cropping.
Future work should encompass further surveys of both conventional, integrated and organic crops to provide information on the current situation. This would provide information on changes in the national agricultural weed flora and an early warning system on the build up of resistance in specific weeds that may not be noticed in a local situation.