Green bridge spreads mildew to spring barley in the north
Record levels of mildew last autumn could mean spring barley in the north of England and Scotland this year is at risk of serious disease infection now, warns Dr Keith Dawson of CSC CropCare.
"Despite a cool March, enough visible mildew infection was still left in winter barley to cross the 'green bridge' into spring barley crops," he says. "In addition there is a very high Rhynchosporium risk. Both diseases can cause severe yield losses so to protect early growth it will pay to spray early."
Dr Dawson believes February mildew levels were the highest for nearly 20 years in winter barley and winter wheat in a mild autumn with well advanced crops.
Although less spring barley was sown in northern regions this year the crop has been drilled into warm soils, encouraging lush growth and disease susceptibility.
Dr Dawson advises growers to assess the risk from mildew, taking account of variety and environmental factors, then use quinoxyfen at a rate that matches the risk.
"As a protectant quinoxyfen fits well. It has no resistance issues in barley and is cheaper than many alternatives. It has great dose flexibility so rate can be tailored to your mildew risk.
"To improve the speed of knockdown, or to cope with Rhynchosporium I would recommend a tank mix with Zenon (spiroxamine). Quinoxyfen is extremely safe in tank mixes, even complicated ones. The product is water-based so it is kind to the plant while being effective on the disease."
With strobilurin resistant barley powdery mildew strains widespread in Scotland he suggests it makes good sense to combine a good chemical strategy with varietal resistance. Quinoxyfen has a different mode of action to strobilurins.
Dr Dawson warns that the spring barley variety Optic, which has shown a dip in mildew resistance over the past few years, still makes up the bulk of the acreage so growers should be careful. Growers should also check Prisma, well-known for its mildew susceptibility, with a reasonable acreage grown on contract in Scotland.
But he also highlights the metabolic disadvantage in varieties 'resistant' to mildew.
"The Mlo gene, which confers mildew resistance, is widespread in spring barley varieties now, but CSC CropCare trials in Scotland and in Denmark have reinforced the widely-held view that these varieties pay a yield penalty, and energy cost, in fighting off the disease.
"The energy cost of resistance in resistant varieties can be reduced by using quinoxyfen, leading to profitable yield responses, covering the costs of the spray in high disease situations," concludes Dr Dawson.
