Research & field trials

A new implement for controlling weeds in cereals, Combcut, has been developed by the organic farmer Jonas Carlsson, Karlskrona, Sweden. The implement cuts weeds in growing cereals without damaging the crop by using the physical differences (in height, stem thickness, straw stiffness, and branching pattern) between crops and weeds. To evaluate the effects of selective cutting on weeds and crops, a number of experiments were performed during the period of 2011-2018.

Selective cutting of Cirsium arvense (L.) Scop. (creeping thistle) was studied in (1) two field experiments (2011, 2012) and one pot experiment (2011-2013) in winter wheat, and (2) in one field experiment with spring barley (2015-2017). The effects of selective cutting of Tripleurospermum inodorum (L.) Sch. Bip. (scentless mayweed) were studied in two field experiments (2012-2013) with grass ley for seed production, and in one field experiment (2012) with winter wheat. Also, selective cutting of Rumex sp. (dock) in pasture, and Thlaspi arvense L. (field penny-cress) in winter wheat was evaluated in field experiments. The evalution of selective cutting of C. arvense in a field experiment with spring barley (2015-2017) was an important part of a PhD-project on the population dynamics of C. arvense. The results were presented at a dissertation in December 2017. Also, a BSc paper on the biology and control of Rumex sp. was produced in 2016. The paper was a part of the study on Rumex sp.

The results showed that selective weed cutting reduced the number of shoots and biomass production of C. arvense in winter wheat and spring barley. Also, selective cutting strongly reduced the seed production of C. arvense. In winter wheat, selective cutting did not reduce the yield while the method increased the yield of spring barley compared with the control. In spring barley, selective cutting was as efficient in reducing above-ground biomass production of C. arvense and increasing spring barley grain yield as herbicide application. Selective cutting of T. inodorum in grass ley for seed production was unsuccessful. No differences in effects were found on weeds or crop compared with the control.

Selective cutting of Rumex sp. in pasture, and T. arvense in winter wheat gave sufficient effects on the weeds. To obtain optimal effects of selective cutting, the method should be used before the occurrence of ear formation of the crop. Also, the weed plants should have reached the stem elongation phase and develop more rigid stems to make it possible to cut off and remove larger amounts of weed biomass. The time period when these physical differences between weeds and crops occur will vary between places and growing seasons. To learn how to use this implement will therefore be a continuous learning process.

The time too is a timing issue. Cutting off must occur after the field thistle begins to stretch to cause mechanical damage to it.
Cutting-off delays the growth and development of the thistle and greatly reduces seed production. In addition, if competition from the crop is added, the production of seeds is further reduced. Combcut can thus also be used to cut off flower and seedbuds and thus counteract seed spread. (87 to 100% reduced amount of flower buds produced).

Weed cutting reduces the amount of biomass produced (above and underground) of the thistle over time. In addition, if competition from a crop is added, the amount of biomass produced decreases. (Above and underground) of the weeds further. (68 to 89% reduced amount of aboveground dry matter (plant) and 66 to 79% reduced amount of underground dry matter (root)

In the pot experiment, the harvest of spring barley increased significantly when cut areas compared to untreated plots (76-94% higher barley harvest).
In the field experiments in 2009, a negative impact of field thistle was found on the crop biomass during the summer, but the field variation was too large to show significant differences in the spring wheat harvest in the autumn between the cut and untreated plots.

Selective weed cutting should be done before the straw shotting of the crop to avoid damageing the crop. This is especially so when you have an aggressive setting on the knives.
In order to have the best effect of Combcut, it´s important to have a competitive  spring cereal crop. This enhances the effect of the cutting so that the thistle is suppressed and the crop benefits even more. This is especially important for large amounts of field thistle.

Om knivarna ställs in på ett mer aggressivt sätt så får man bättre effekt på åkertistel men också ökad risk för skador på vårsädesgrödan.
It the setting of the knives is more aggressive, there´s a positive effect on the thistle but there´s also a higher risk of damageing the crop.