Arable farms where there has been little spring cropping are where the broad-leaved weed bur chervil is making its presence felt, and has become a serious problem in areas of Wiltshire, Oxfordshire, Hampshire and the Midlands. But more winter wheat being drilled due to favourable prices and less spring cereal seed being available, could exacerbate the situation for next year and beyond.
AICC agronomist Steve Cook of Hampshire Arable Systems says these vigorous broad-leaved weeds must be controlled early in the spring when small and actively growing with a high loading of SU such as Harmony M SX (40g/kg metsulfuron-methyl and 400g/kg thifensulfuron-methyl) and Ally Max SX (143g/kg metsulfuron-methyl and 143g/kg tribenuron-methyl).
Both approaches have been successful in the past but the highly aggressive and competitive nature of bur chervil means that he has had to improve the efficacy. Before its revocation, flupyrsulfuron was a useful option for suppressing bur chervil, but this now has to be left to Spitfire (fluroxypyr + florasulam) applied in the autumn. Spring applied herbicides now present the best chances of control, according to Mr Cook.
“A more prescriptively tailored herbicide programme is essential to get on top of this highly competitive weed and its cousin, the slightly less ubiquitous, but equally yield-robbing and invasive wild carrot,” says Mr Cook.
Bur chervil is very prolific with large numbers of seeds being returned to the soil profile. It normally appears in patches having started as a hedgerow weed. Harvesting the headlands and spreading straw and chaff has exacerbated the situation, although the lack of available chemistry in oilseed rape has also been a contributory factor towards both weeds gaining prevalence.
It is more common on lighter land but the impact is now being felt on heavier soils too. Mr Cook says that sewage heaps appear to promote bur chervil so it might be that it likes very fertile soils and where the wheat does not invariably grow the weed takes advantage.
“Bur chervil leaves look similar to parsley, but if you pull it up and crush the root it smells a bit like carrot,” says Mr Cook. “It will smother a crop when dense and at harvest it is green so can hinder the combine.”
In the past, autumn herbicides such as IPU and CTL were effective at controlling grass weeds and some autumn germinating broad-leaved weeds.
“They were excellent at taking out most of the indigenous weeds, but losing these chemicals is giving rise to selection pressure,” explains Mr Cook. “There isn’t any resistance yet to the SUs so it’s critical to maximise cultural control options to reduce the dependence on the limited specific herbicides that we have left in the armory.
“In oilseed rape we have Belkar (Arylex + picloram) and Astrokerb (propyzamide + aminopyralid) which do knock bur chervil, but there’s nothing to really take it out,” he says. “It’s normally a localised problem with very dense patches appearing. In cereals the strategy must be to control it early. There is no follow up option after the spring and so even if spraying is delayed it would still pay in my opinion to go with Harmony M.
“If bur chervil can’t be dealt with by GS31 then you’re looking at partial or even minimal control, which translates into yield loss, lower margins and ultimately more weed seed being returned to the bank,” says Mr Cook.
In Autumn 2018 he had not seen as much bur chervil as expected and this might have been due to better control last year and more time for stale seedbeds following an early harvest.
“Growers are more aware of the problem now than a few years ago so have become better at controlling it,” he says.