2013 ASHS Annual Conference

Organic vegetable growers rely on cover crops to contribute to their weed management by reducing weed seed rain and increasing weed seed mortality. We investigated whether late-summer planting of cover crops in the Great Lakes region would reduce fall weed escapes and subsequent weed growth in the following year’s crop.  We also investigated whether the effect of a late-summer cover crop is different if it is allowed to decompose over winter with the roots undisturbed or incorporated in the fall so that it is thoroughly decomposed. Furthermore, untreated bean seed is susceptible to many rot pathogens whose abundance might be affected differently by the various cover crop species, and by how recently and rapidly the decomposition occurred. To obtain results applicable to the broader Great Lakes region, we performed the experiment in New York, Michigan, and Illinois using organic practices. While fall tillage resulted in substantially lower stands of beans, that effect was the same whether there was a cover crop present or not.  In spring-incorporated plots the stand was slightly better following sudangrass, with the other cover crops being equivalent to no cover crop. Fall weeds, and therefore, weed seed rain, were strongly suppressed by cover crops. The weed biomass was less than 20% of the unmanaged plots. Sudangrass was effective when it emerged quickly, but when drought delayed its emergence, sudangrass failed to suppress weed establishment. Buckwheat, which was terminated in September, allowed some cool-season grasses to establish afterwards. Weed pressure in the bean crop was measured in several ways relevant to a growers’ weed management: initial flush of seedlings, post-cultivation emergence, and time required to hand weed after mechanical cultivation. There was no consistent effect of any cover crop on the subsequent weed pressure. At an individual site and year, there were sometimes large effects that may indicate a suppression mechanism that would be useable if it could be identified. While these cover crops were effective for reducing the weed seed production, and would therefore be valuable in long-term weed minimization, the benefit was not consistently detectable in the subsequent year.