Trials to uncover the impact of growing two oilseed rape crops back-to-back in a bid to combat black-grass are being carried out at Frontier Agriculture’s Abbots Ripton site.
Following a model adopted in Australia by farmer Mic Fels to tackle herbicide resistant ryegrass, the oilseed rape sequence maximises the opportunity to use herbicides which are not showing signs of resistance, where soil type means spring cropping is not always a viable option.
Dr Paul Fogg, crop production technical lead at Frontier, explains: “When it comes to black-grass it is all about an integrated approach and things you can do differently. These trials build on the concept of stacking chemistry in our favour while not being entirely reliant.
“With oilseed rape, we have got at least two active ingredients where there is no resistance identified, which gives us a great opportunity to use non-resistant chemistry within the oilseed rape crop,” says Dr Fogg. “We do back-to-back cereals routinely and stack residuals in our favour, so why not consider doing the same in oilseed rape?”
By growing a conventional OSR variety in the first year, followed by a Clearfield variety in the second, Dr Fogg says the aim is to use three key actives more strategically within the rotation to get better overall black-grass control. The herbicide stack in trials include an early clethodim treatment, followed by Crawler (carbetamide) and propyzamide.
Now in its second year of OSR, the field which has been double cropped is showing similar black-grass control to its partner field which has been grown within a conventional rotation after winter wheat. This is what you would expect at this stage says Jeremy Ruff agronomist at Frontier, who is leading the trials.
“Going forward, if this was to become the norm we would start to reduce the seed bank and get better overall black-grass control through cutting seed return.”
The second objective of the trials is to determine whether other issues arise from increased disease and insect pressure.
Comparing the double OSR crop with the neighbouring crop, Mr Ruff says: “Both crops have had near identical herbicides but what I am more interested in is whether anything is going to come back and bite us disease or pathology wise. The principal is simple enough, but this is the big question growing two OSR crops back-to-back.”
At present leaf spot and phoma levels are no different to the adjacent field says Mr Ruff.
“If anything, we are watching out for verticillium which could be an issue, but there are no visible symptoms.”
The risk of clubroot is higher with the introduction of a second OSR crop, but Mr Ruff says none has been detected, although it may be too early to tell.
“We have had reports of clubroot around the country, but from what we have pulled up there is no visible issue and it is looking very well indeed. If it is a problem we would have to pick varieties that are more tolerant.”
Neither crops have been heavily hit by cabbage stem flea beetle attack which Mr Ruff puts down to early drilling.
“It is almost conspicuous by its absence. There are a few holes in leaf petioles but certainly nothing in the main stem. It might be luck of the season – crops were established relatively early into good seedbeds and got away well.”
Growing a conventional OSR variety in the first year and a Clearfield variety in the second year means volunteers are cleared up, which Mr Ruff hopes will further reduce disease pressure.
“This theory is beautifully simple and control is looking very good,” says Mr Ruff. “It probably gives you a better return than chucking in spring barley which can crash and burn, and it can have a late flush of black-grass, so you end up back at square one.
“If it proves to be advantages, theoretically two OSR crops followed by beans, a couple of wheat crops, a barley and back into OSR could well be an option going forward.
“So far, there is no eureka moment but there are no negatives. Ultimately we will follow it to harvest and see if anything else comes through.”
Drilling date: August 19
Variety: DK Imperial