Article taken from Crop Production Magazine, written by Lucy de la Pasture.
Establishing oilseed rape can be a risky business and this season is proving to be no exception. New post-emergence herbicide Belkar (halauxifen-methyl+ picloram) may have arrived just too late this season to benefit many growers, but those that have already gained some experience using it are poised for a shift in their herbicide strategy.
Both of the active ingredients in Belkar are already familiar to arable growers, with Arylex Active the key molecule in cereal herbicides Pixxaro (Arylex+ fluoroxypyr) and Zypar (Arylex+ florasulam), and picloram, known to growers as one of the actives in spring-applied OSR herbicide, Galera (clopyralid+ picloram).
Targeting cleavers, cranesbill, poppy, shepherd's purse and fumitory, Belkar offers an alternative to the traditional pre-emergence sprays. Instead, growers can wait until the crop is out the ground - giving themselves time to assess the visible weed pressure plus the impact of cabbage stem flea beetle and slugs.
This year is a good case in point, says Agrovista's technical manager, Mark Hemmant. ""Warm, dry soils have provided good conditions for the pest and poor conditions for the crop, leaving flea beetles happily munching away.""
Crop failure
And it's that very real risk of crop failure with OSR that makes growers reluctant to fork out on pre-em herbicides. For this reason, the approval of a new post-em herbicide will provide a new option for growers, comments Mark.
""As well as the cost involved, use of a pre-em can limit following crop options in the event of a crop failure."" he adds.
Andrew Cragg from 600ha Brooker Farms on Kent's Romney Marshes held product trials through the winter of 2017 and says the chemistry will lead to a change of approach. ""There's very little chemistry in the armoury that will control all of the problems we have in the OSR crop," he says.
""Cranesbill, chickweed, blackgrass and volunteer cereals are what I'm looking to deal with, and that has typically taken applications of clomazone or a pre and post-emergence spray of metazachlor.
That would be followed by propyzamide and aminopyralid. It's become a real task to get to grips with everything.""
Andrew says he's got used to front-loading his herbicides but that the strategy is 'risky because you don't know if the crop is going to arrive.'
""I have seen the trials demonstrate very good control of cranesbill and cleavers and it means I can deal with them once the crop is up. I'm happy to invest if I know it's going to have an output and I think other growers will have no problem moving to a post-em regime if that means they don't have to invest in a crop that they don't know will be there.""
Peter Waite, national account manager at Corteva, says a product with Belkar's properties has been demanded by the market for some time.
""We first got approval for Arylex in cereals in 2015 and when agronomists saw that it controlled cleavers and cranesbill but not brassicas, the question quickly came about when it would be available in OSR.
""Now it has approval, we think it will be at the forefront of growers' minds in the future because heavy investment in pre-em sprays is risky when you have cabbage stem flea beetle to contend with and, in
a wet autumn, slugs.""
There are three treatment options which Corteva says have performed best in trials.
""At two true leaves an application at 0.25 I/ha will take out the weeds which have germinated alongside the crop and, in some circumstances, that will be enough broadleaf weed control before an application of Astrokerb (propyzamide+ aminopyralid) or similar later on.
""In high weed pressure situations where you get a second germination you can do a second 0.25 I/ha two-to-four weeks after the first.
""A third option where you have a low-pressure situation is to wait until six true leaves of the crop and apply 0.5 I/ha which will take care of the weeds going into the autumn.""
Mark believes the best approach is using the split dose and Agrovista trials have demonstrated that the addition of Parish (phenmedipham) at the two true leaf stage of the crop is worthwhile to broaden the
weed spectrum.
""We've seen significant improvements in the control of chickweed, speedwell and groundsel and poppy, particularly when it has become larger than ideal ( <2cm).
Parish needs sunny conditions at the time of application so it's best suited to the early timing and the mix is supported on the product label," he adds.
One of the main strengths of Belkar is its activity on cranesbill, a weed other OSR herbicides struggle to control. ""Fox (bifenox) has an EAMU for control of Geranium sp. in OSR after the six true-leaf stage of the crop but control tends to be variable," he comments.
Cranesbill is mostly a heavy land weed so often occurs hand in hand with blackgrass, adds Mark. ""Ideally a pre-em of metazachlor would be an advisable strategy but if there's a reluctance to spend at that timing then ""With graminicide Centurion Max (clethodim) and Belkar both having a label recommendation to apply from the two true leaf stage of the crop, the biggest thing to consider is sequencing them. Centurion Max needs two clear weeks either side of application and must be applied by 15 Oct," he points out.
""Belkar can be applied from 1 Sept until the end of Dec but in most situations grassweed control will take priority, unless cranesbill is the over-riding problem.""
Peter adds a full launch of Belkar will take place ahead of 2019 applications because its approval was granted too late in the day to supply product in any quantity this autumn.