The potential for white mustard to reduce the level of cabbage stem flea beetle grazing in oilseed rape when grown as a companion crop is to be investigated in a series of BASF-sponsored trials.

The aim is to help farmers cope with pest pressures in light of the partial ban on three neonicotinoid insecticides, which is expected to be strengthened to cover all outdoor use of the controversial insecticides later this year.

Small plot experiments in recent seasons have suggested white mustard grown amongst or next to OSR plants may reduce grazing damage by adult beetles. NIAB TAG has pioneered this work, carrying out two years of successive trials looking at different options that might prove to be effective companion crops. Amongst these options, white mustard was deemed to have the greatest potential.

NIAB TAG will be extending its work on the concept this season, both independently and in collaboration with BASF. In parallel, BASF is also setting up its own grower trials to test the concept further.

Several seed rates will be assessed in both trials, to help identify optimum white mustard populations that offer the best degree of protection while causing least competitive impact to the oilseed rape crop, explained Clare Tucker, Business Development Manager for BASF. Ms Tucker said, “It’s important to do detailed research on this since it’s a fine balance between being an effective deterrent to the beetle whilst not damaging yield potential – white mustard is a vigorous plant.”

Both sets of BASF-sponsored trials will use Clearfield oilseed rape varieties that will enable the white mustard to be controlled effectively with Clearfield herbicides without risk of crop damage, once the OSR is established and beyond the high-risk period of adult grazing.

“It’s not enough for a companion crop to reduce pest pressure at the critical time. Growers also have to be able to remove it from the crop, otherwise it can compete and affect yields,” said Claire, “Clearfield gives good control of white mustard, so it’s a good option.”

Simon Kightley, NIAB TAG’s oilseed rape specialist, said experiments carried out in 2015 and 2016 indicated some scope for reducing grazing damage by the adult beetles, with white mustard showing the most promise. He said at one site near Cambridge, this technique provided the only protection for OSR plants in 2016, when all other OSR trials and OSR mixtures in companion crop experiments were wiped out by flea beetles.

Mr Knightley said, “I am really excited about this discovery. In a field of 24ha the only surviving plants last year were within a small number of plots with the white mustard mix. I just can’t wait to get going with the new planting season to validate the concept.”

The trials will be conducted at three different sites this year. Plant counts and feeding damage assessments will be taken from emergence through the following two months. Larval counts will be taken in early spring, and plots will be taken to yield.