Winter and spring beans give potential for black-grass control
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“Winter and spring beans give potential for black-grass control in addition to the other benefits from pulse crops,” says Jim Scrimshaw PGRO principal technical officer. “With disappointing black-grass control in a cereal crop costing perhaps over £100/ha, pulse crops can potentially give some robust stacking and sequencing options – and they also usefully diversify the rotation, spread the work load, provide additional nitrogen and increase yield in the following cereal crop.”
He explains that increasing incidences of resistance mean that chemically controlling black-grass in cereals is becoming less and less dependable with some products. With no new chemistry in the pipeline, strategies that involve the 'stacking' and 'sequencing' of existing products along with using cultural techniques should be considered together to keep on top of the problem.
The majority of black-grass seed germinates from the upper few centimetres of soil. If there has been a high seed return, then ploughing can bury seed to a depth from which germination is unlikely. However, there is the potential to plough viable seed to the surface, depending on distribution within the soil profile. Past knowledge of the problem and the cultivations used is useful.
Light cultivations and consolidation can stimulate black-grass germination and allow glyphosate sprays to be used before direct drilling crops, he says. Before a spring crop such as field beans or peas, depending on seed dormancy and the season, it may be possible to spray off up to three flushes and dramatically reduce the black-grass population. Rotations including spring crops can to help reduce grass weed problems in general.
“If considering winter beans, their later drilling window compared to oilseed rape or a second cereal, may allow a flush of weed to be sprayed off before putting the crop in the ground. We also have Crawler (carbetamide) and Kerb (propyzamide) available for use in winter beans to which there are no known black-grass resistance issues. “There is the opportunity to use either or both these products pre-emergence, and Crawler post-emergence, up to the end of February. Work from HGCA has shown that the most robust means of chemical control of black-grass centres on timely applications (cooler conditions for Kerb) of these products. In cereals flufenacet, pendimethalin, tri-allate and prosulfocarb are the backbone of many chemical strategies.
“All, except flufenacet, are permitted for use in winter beans (and spring) beans, to give potentially some robust stacking and sequencing options. These are not cheap chemical options – but to stress the point made earlier – with disappointing black-grass control in a cereal costing perhaps over £100/ha the opportunity to use propyzamide and carbetamide + others, in a crop which will also usefully diversify the rotation, spread the work load, provide additional nitrogen and increase yield in the following cereal must be worth considering. And have value if subsequently black-grass doesn't have to be the main concern.”