Weeds in grassland can reduce the forage yield and reduce or increase the forage quality depending on the amount and species present. The weed proportion tends to increase as the grassland ages, increasing the need for grassland renewal with herbicides and/or tillage. Norwegian farmers are obligated to use integrated pest management (IPM). The overall goal of the project was to contribute to the development of IPM in forage production and to find cost-effective strategies for weed control that provide high forage yield with less use of pesticides. In field trials from southern to northern Norway, we investigated how fallowing, tillage, sowing and herbicide strategies affected weeds, clover and grass crops in the sowing year and subsequent ley years. Crop yield, feed quality and profitability were also estimated. In established grassland, the effect of selective weed cutting was studied in Norway and Sweden. The project provides knowledge relevant also for organic farming.
Use of a cereal companion crop and selective herbicides resulted in lower weed abundance, while the use of glyphosate+rotavator more weeds than glyphosate+ploughing in two out of three trials. In the first ley year, the rotavator resulted in a lower forage yield than ploughing. When establishing the grassland in summer rather than spring, the crop and weed quantity in the first ley year were lower in the Northernmost field, but not in the two Southern fields. In the second and third ley years there were minor differences in forage yield between treatments. Fallowing with glyphosate in autumn (only studied in a field in central Norway) gave higher grain yield of cereals sown as a companion crop the following spring compared to no fallowing with glyphosate, while in subsequent years there was no difference in forage yield. Autumn fallowing also resulted in fewer weed in the sowing year than other treatments.
To estimate how the weed content affected forage quality and thus the economic value of the forage, we analysed the quality of the dominating weed species harvested at all cuts in 2015 and 2016. The quality of Rumex spp. was very low, especially in the second and third harvest. In the first harvest, the plants were less developed and thus a bit more digestible. A forage model was run together with climate data for the relevant harvest times to estimate the quality of weed-free grassland.
Profitability estimations from long-term trials suggested that selective herbicides in new sown ley was often profitable. It was most profitable in spring without a cereal companion crop and least with a companion crop. However, the use of a cereal companion crop was in itself profitable if it was harvested as ripe grain. It was not profitable to use glyphosate in late spring because of loss of crop yield in the sowing year. Glyphosate in autumn before spring sowing had good profitability. The rotavator was only competitive with ploughing in one out of three fields. Summer sowing was most profitable in the south, spring sowing in the north, but less clear in central Norway.
Separate experiments with various herbicides for fallowing before ploughing of the grassland, showed a reduced glyphosate dose can control dicot weeds, such as Rumex spp, when mixed with selective herbicides. Ploughing also had a good effect on the weeds in the first ley year, but tillage can stimulate seed germination of Rumex spp. The effect of fallowing will be more short-lived if newly emerged weeds are not controlled. The forage yield in the first year was hardly influenced by the fallow strategies.
Various herbicides with and without cereal companion crop were investigated in several trials. The cereals resulted in large reduction in weed, grass and clover coverage in the seeding year, while the effect was lower in the first ley year. If the cereal was vigorous, the forage yield was reduced in the first ley year. Clover was, as expected, damaged by some herbicides, but the effect of the herbicides on weeds was similar. The forage yield in the first ley year was not affected by the herbicides.
In trials with different sowing methods and rates of grass-clover mixture, with and without cereal companion crop in northern Norway, the cereals competed well with the weeds. The dry matter forage yield increased with increasing degree (later harvests) of cereal companion crop in the sowing year. In the first ley year, however, there was a negative effect of companion crop on dry matter yields. In the second and third ley years effect of the cereals on forage yield was gone. Cross-sowing of the grass-clover mixture gave a higher yield than sowing in rows.
Several field trials were conducted with the selective weed cutter CombCut to control Rumex spp. in established meadow. The effect was variable, from poor to decent. More knowledge is needed on technical adjustment and timing to achieve sufficient selectivity. A promising result was that the CombCut did not reduce the crop yield.
Virkninger av prosjektet er at prosjektdeltakerne har fått økt kompetanse om fornying av eng på ugras, grovfôravling, kvalitet og lønnsomhet og styrket samarbeid både nasjonalt og internasjonalt. Det har vært omfattende rådgiving til bønder i prosjektet. Vi har fått bekrefta at gamle råd fremdeles er gyldige, som at ugrasbekjemping i gjenlegget er viktig for å forsinke ugrasutviklinga i enga og betydningen av god agronomi (pløying og rotorharving med god presisjon, sprøyting ved optimale forhold, godt såbed). Nytt er det at dette har blitt bekrefta av lønnsomhetsberegninger. Bruken av glyfosat er omdiskutert og kan ved brakking reduseres ved å blande med andre ugrasmidler. Prosjektet har gitt verdifull kunnskap for integrert plantevern og økologisk dyrking. Dekkvekst kan redusere ugras og kryss-såing kan være gunstig i økologisk dyrking. Selektiv ugrasskjæring i grasmark kan nyttes i økologisk dyrking i stedet for herbicider. Det kreves imidlertid mer forsking før dette kan anbefales.
There is an aim in Norway to increase forage production. Weeds in grasslands can influence forage yield and quality in both directions depending on amount of weeds and weed species. The main objective in this project is to develop integrated weed manageme nt strategies that sustain high forage yields for livestock and involve minimal use of herbicides. We hypothesize that weed control strategies in the renewal phase will reduce the need of herbicides in the subsequent ley years and will lead to higher fora ge yields and profitability. This will be obtained in field trials in major forage producing areas in Norway to increase knowledge (i) how different methods for fallowing and seed bed preparation affects weed establishment in the seeding year and subseque nt ley period, (ii) how crop competitive ability, seeding methods and herbicides influence establishment of grass and clover and control of weed seedlings in the seeding year and how this impact first year ley yield, (iii) knowledge of innovative mechanic al measures for weed control in the ley years. Forage quality and economic return of different management strategies from the field trials will be estimated. The results will be disseminated to advisors and growers to increase knowledge and use of effecti ve and profitable integrated weed management strategies. The project will give valuable knowledge for organic production as well.