As the crop variety trials progress in wheat, oats and now beans, and I spend more and more time on organic farms, I have started to wonder whether crop competition may be an under valued management option for weed control.
Groundcover is a very valuable trait for suppressing weeds. We have found a direct link in our research trials between higher crop groundcover and lower weed groundcover. In fact, despite the commonly held belief that crop height is what's needed for competition, and this may well be true of later weeds, it''s the competition provided by the crop early in the growing season that makes the real difference to weed suppression. Many believe crop height to be the most significant trait for weed control but it's actually good groundcover and early vigour that provides the best suppression.
High ground cover can be achieved in different ways. Drilling scheme is the most obvious way to manage groundcover, with narrow rows being better at covering ground than wider rows. Cross drilling could maximise the groundcover from the emerging crop but still remains an underutilised practice. High seed rates, giving higher plant populations, will also lead to higher groundcover.
Crop species and variety are also important choices. Species that are weed suppressive include Oats, Rye, Triticale and Barley and Spring cropping is likely to control weeds better than winter cropping. One of the stand out results from this season of the LiveWheat Legacy trials has been to discover a very weed suppressive winter wheat, cv Mayflower, with a prostrate growth habit, leading to, higher ground cover in the critical stages of the season. Early vigour is also an important trait for weed suppression, and the wheat variety Extase possess this traits making it an excellent organic option. Our trials with spring beans have also revealed there are even bean cultivars that are more suppressive than others, possibly due to branch angle and leaf size shading out weeds better. The variety Victus appears to be more weed suppressive than the other varieties tested, most notably, Lynx.
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