Weed seed dormancy poses important decisions on herbicide choice

UK - September 27, 2004

Oilseed rape growers need to take account of the protracted germination period for many broad-leaved and grass weeds in the past season to avoid weed control disappointment in the coming year, warns Dow AgroSciences.

Interim results from the Sustainable Arable LINK program at ADAS Boxworth show that dormancy in black-grass seed samples this autumn is high. Black-grass samples taken from 20 sites in 2004 show just 28% had germinated compared to 57% in the previous season when the weather was hot and dry as the weed seeds ripened.

Sarah Cook of ADAS Boxworth says, “Our work to date shows that dormant black-grass seeds only germinate after six weeks. Evidence from past work shows that black-grass seed which remains dormant in autumn can germinate early in the following spring. Therefore herbicide programs with a strong residual element are likely to be beneficial.”

Dow AgroSciences point out that for reliable control of resistant black-grass in winter rape and winter beans, Kerb* products, containing propyzamide, are the most persistent of the residual choices available.

In addition, there is also likely to be a very protracted period of cleavers emergence in winter rape. Therefore, decisions on cleavers control should be delayed until spring when Galera*, containing clopyralid and picloram, will provide up to 80% control of cleavers.

^† Trademark of The Dow Chemical Company