Archive Article: 2001/10/20
Headache for oilseed rape
TARGET site resistant blackgrass is a bigger headache in oilseed rape than wheat, according to ADASs David Parish. Some of his Bedfordshire farming clients are switching to winter beans in order to take advantage of the opportunity to plough and kill the first weed flush with glyphosate.
He is very concerned about the increasing incidence of target site resistant blackgrass and estimates that probably 75% of his clients farms have it at some level, although not in all fields. Samples analysed at ADAS Boxwoth show that in 1999, 30% of samples analysed were target site resistant. In 2000 this leapt to 50% and is now 53% this season, although fewer blackgrass samples have been analysed.
Target site resistant blackgrass limits product choice in oilseed rape "Once you have taken out Aramo, Laser, Falcon, Fusilade and Pilot (fops and dims) from your weed control armoury you are only left with trifluralin, Butisan, Kerb or Carbetamex."
They all have their limitations: "Trifluralin needs incorporating into the soil. Butisan cannot be used pre-emergence where oilseed rape crops are broadcast or Autocast. Kerb and Carbetamex cannot be applied before 1 October; by then blackgrass plants may already be tillering. In good conditions Kerb can give good control, but in a dry autumn or on deep-rooted blackgrass it can be less effective. Carbetamex is more soluble than Kerb so can be less effective in wet winters."
So what should growers do? Key areas to address include:
1 Cultural controls
The importance of controlling weeds pre-drilling cannot be overstated. But it is hard work to do; given recent autumns it is more tempting to drill than wait 24 hours to spray off an early weed flush
2 Gear product strategy to residuals
Avadex, Crystal, Stomp and Lexus post emergence as well as chlortoluron and ipu give residual activity. Unfortunately enhanced metabolic resistant blackgrass are tolerant, to varying degrees, to this group of herbicides
3 Quality of seedbed
The residual route rests entirely on obtaining a good seedbed; without it, the effectiveness of these products falls off rapidly. Also ensure an adequate drilling depth so that the choice of herbicide is not limited
4 Choice of break crop
Achieving control of target site resistant blackgrass in oilseed rape is become increasingly difficult. Winter beans offer greater cultural and product flexibility