FRESHSTRATEGYFORRHYNCHOWANTED…
FRESHSTRATEGYFORRHYNCHOWANTED…
Its stacking up to be a
bad rhynchosporium year –
just when theres more
spring barley. Better
disease control is needed
TRIAZOLE fungicides are now far less effective against rhynchosporium than they were just two or three seasons ago, so a new strategy is needed for 2001, says SAC Edinburgh pathologist Simon Oxley.
After a lot of infection in crops last year, plenty of barley volunteers to carry it through the winter, and a huge spring barley crop expected this year, rhynchosporium pressure is likely to be high, he says.
If the early part of the season is wet the fungus could be particularly troublesome.
"Rhynchosporium likes wet conditions, so has flourished in recent seasons," says Dr Oxley. "This increased disease pressure and lack of effective resistance in modern barley varieties could explain why triazoles are now less effective than previously.
"There seems to have been a shift in the sensitivity of the fungal populations to them, and in areas of intensive barley production, such as parts of Scotland, a few cases of resistance have been confirmed."
A build-up of barley volunteers as growers have switched to min-till establishment could be contributing to the growing rhynchosporium threat, Dr Oxley believes.
The disease affects spring crops early in the season and can lead to massive yield loss, particularly if it is allowed to infect the crop at or around tillering.
If that happens complete defoliation of plants leading to almost total crop loss can occur. But even moderate infections can be costly, as any loss of green leaf area can compromise grain fill, leading to a high level of screenings.
It is important to treat the spring crop early, at tillering, before any sign of the disease is seen, Dr Oxley notes. Once the fungus is allowed to gain a foothold fungicides are not powerful enough to kill it. The range of available fungicides only provides protection, they do not have eradicant activity.
In a three-year HGCA-funded project, which started last March, SAC Edinburgh is looking at the contribution individual fungicides make to rhynchosporium control, and which mixtures are the most effective.
"Where still effective, triazoles have a role to play in proving protection against the disease. Although most have been compromised by the fungal populations shift in sensitivity Unix has not been affected and remains an important option. It is now regarded as a core fungicide for controlling the damaging disease.
"But as it cannot be used on its own, it should be partnered with a strobilurin or the morpholine Corbel. Morpholines give very little control of rhynchosporium but when used in a mixture they provide an enhanced kick-start to the protection of plants," Dr Oxley says. *
RHYNCHO RISKS
• Rhynchosporium risk increasing.
• Devastating crop losses possible.
• Infections can occur early.
• Most triazoles less effective than before.
• Some resistance confirmed.
• Strobilurin use recommended.