Autumn mowing and pelargonic acid can suppress Elymus repens abundance especially when combined with increased crop competition

Abstract

Couch grass (Elymus repens) is a creeping perennial weed that can cause great yield losses in a wide range of crops. Established stands are usually controlled by glyphosate, selective herbicides, or intensive tillage. Many herbicides, including glyphosate, are, however, currently at risk of being banned. Couch grass can be controlled with below-ground tillage treatments to a depth of 10-15 cm, followed with mouldboard ploughing at a depth of 20-25 cm. Mowing is sometimes used, but often with unsatisfactory results. We wanted to test if there was a better effect of combining a bio-herbicide with autumn mowing and if increased crop competition could further enhance efficacy. One field experiment was carried out in Norway with combinations of bio-herbicide, mowing and competition (cross-sowing of spring cereals) in 2019-2021 and one in Finland with mowing and bio-herbicide in 2019-2020. Pelargonic acid (Beloukha, 680 g a.i. L-1, dose rate 16 L ha-1) was used as bio-herbicide. Couch abundance in autumn, in early and late spring and finally before spring cereal harvest were assessed. In general, each of the treatments caused up to 25-50% short-term reduction in ground cover. The best effect against couch grass was achieved by the combination of all three treatments, with nearly 70% reduction in dry matter in the subsequent summer sampling. However, no treatment combination could reach the same level of efficacy that could be expected with glyphosate.

Keywords

• bio-herbicide
• couch grass
• mechanical weed control
• perennial weeds