“Winter and Spring Beans give potential for blackgrass control in addition to the other benefits from pulse crops,” says Jim Scrimshaw PGRO Principal Technical Officer. “With disappointing blackgrass 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 blackgrass 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 blackgrass 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 blackgrass germination and allow glyphosate sprays to be used before direct drilling crops. 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 blackgrass 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 blackgrass 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 blackgrass 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 blackgrass 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 blackgrass doesn't have to be the main concern.
“Graminicides such as Laser (cycloxydim) and Aramo (tepraloxydim) can be useful post-emergence in both the spring and winter pulse crops mentioned. Laser can control enhanced metabolism populations and Aramo also has activity on target site resistant populations. Dramatically lower numbers from either more cultural techniques, (spring crops) and /or chemically sensitised blackgrass, (winter beans) would, hopefully, mean more effective control from these materials if required,” adds Mr Scrimshaw.
