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How does tillage affect weed regulation by seed eaters?

Published: 13 November 2023
A thistle in an agricultural field. Photo.

Carabid beetles are a group of beetles that eat weed seeds. In a new study, the abundance of carabid beetles has been shown to be correlated to weed seed regulation in directly seeded fields without tilling, indicating a role of carabids in regulating weed seeds in these fields.

Weeds cause major yield losses despite frequent use of herbicides. Carabid beetles are frequent consumers of weed seeds, thus potentially offering important biological control services and regulating weed populations. While it is known that soil tillage can negatively affect carabids and their predation of weed seeds it is not known if this translates into regulation of weed populations. Ola Lundin from the Department of Ecology got a grant from SLU Centre for Biological Control in 2021 to investigate this.

– We sampled 30 winter oilseed rape fields in Västergötland in 2021.  Ten winter oilseed rape crops each had been established following ploughing, reduced tillage or with no-till.

Carabid beetles and weeds were identified

Then, Ola and co-workers took soil samples in March and August and put them in the greenhouse for germination, growth and identification of weeds. Aboveground seed abundance was sampled via suction sampling in June and July and the numbers of seeds was counted in the laboratory.

Carabid beetles were sampled with pitfall traps in May, June and July. Specimens were identified and counted in the laboratory. Annual meadow grass (Poa annua) was the most common weed in the seed bank. Weed seed abundance in the soil banks did not differ between tillage treatments, but weed seed abundance on the surface was lower with reduced tillage. Carabid abundance and richness did also not differ between the tillage treatments.

– The reason for this may be that the beetles had time to recover from the disturbance and recolonize the fields following the tillage which was performed in the year prior to sampling, says Ola.

More carabid beetles resulted in less weed seeds

Carabid abundance was correlated to weed seed regulation in directly seeded (no-till) fields, indicating a role of carabids in regulating weed seeds in these fields.

On November 13, Eirini Lamprini Daouti from the Department of Crop Production Ecology held a webinar, arranged by SLU Plant Protection Network and SLU Center for Biological Control, and talked about the results. This project is part of a larger project investigating weed predation in different ways.

– Going forward, we will also look at how herbicides have been used in the different fields and what impact this has on the results, Eirini said.