As weeds become harder to control than ever before, farmers are having to rethink their options. The Soil Association held a non-chemical weed control day to demonstrate how herbicides can be the last tool to reach for.
Although herbicides are the second most costly input on most farms after fertiliser spend, they are being used less effectively. This is according to Prof Nicola Cannon of the Royal Agricultural University (RAU), who outlined the financial implications of managing weeds in arable rotations.
Using the RAU farms as an example, a conventional field of winter wheat last year, yielding 9.6 tonnes per hectare and sold at £135/t had a gross margin of £679/ha.
Prof Cannon said: “Herbicide spend made up £184/ha, £60/ha more than NIAB 2020 gross margin forecasts. The field still has weeds, predominantly black-grass, and we are still seeing a yield penalty.”
Prof Cannon compared this figure to one from one of the university’s organic fields, which yielded just 2.7t/ha, but had much lower input costs. The gross margin was £672/ha with the organic wheat sold at £280/t.
“The comparison in the simple gross margins are only within a stone throw of each other,” Prof Cannon said.
“This is a national trend. Looking at Defra data from this year, we can see the productivity from the use of inputs has declined while outputs have increased somewhat. We are using them less effectively.
“Herbicides should be the last tool in the toolbox to take effect – we cannot have them as the primary tool. We need to have more alternatives – whether that is mechanical weed control or other methods.”
This means: Five meadow-grass plants, 10 black-grass, two speedwell, and one chickweed in one sq.m would create a yield loss of 4.86 per cent, the equivalent of £65/ha.
Source: Prof Nicola Cannon, Royal Agricultural University