15 January 1999

Organic system needs the right weed control…

WHEN you cant get cereal weed control out of a can it is vital to limit risk to yield and quality by choosing the optimum management package. That can be very challenging for stockless organic systems which lack a grass break, delegates at the Soil Associations annual conference heard.

"An even and rapid crop establishment is vital to a successful organic system," commented Lois Phillips of Elm Farm Research Centre. In an 11-year trial at the centre yields of rotational wheat declined from year four to seven but then picked up. That was partly due to improved drilling techniques which resulted in a more even crop and reduced weed competition.

In addition, the correct selection of rotation, variety, sowing date, use of a false seed bed, crop density, and mechanical weed control all affect final weed infestation, said Elm Farms James Walsh. Trials with wheat on the heavy soil infested with blackgrass and mayweed showed the "critical period" for weed control is November to March. But wet autumns seriously challenge scratch weeding, especially on heavy soils, he added.

Delaying control until the spring also makes wiry rooted weeds like poppy, difficult to control with scratch weeding. An alternative is inter-row hoeing with cereals sown at 25-30cm (10-15in) centres. But although the technique is effective and less time sensitive, it is more expensive and slow, said Mr Welsh.

"It needs a good driver and machinery otherwise some of the crop goes as well as the weeds." However, trials on a commercial scale, using a centre steer tractor for accuracy have given very good yield response at a range of timings, as well as releasing nitrogen which in turn improves grain protein, he said.