Act now to keep take-all threat at bay, is advice
By Andrew Blake
COPING with take-all successfully will be crucial if Agenda 2000 proposals prompt the widely expected move to much more cereal cropping.
To help growers assess whether a novel seed treatment is justified, fungicide maker Monsanto is working with ADAS and Arable Research Centres to understand husbandry defences and the disease risk on individual farms better.
The root-scissoring fungus is a key reason for second wheats yielding 10-15% below first wheats, a loss which costs the UK £80m a year, says John Spink of ADAS Rosemaund. "The average yield loss due to take-all is probably 1t/ha in second wheats."
Agenda 2000s proposed reduction in oilseeds support is likely to boost the area of take-all prone second and subsequent wheats, adds the Arable Research Centres Stuart Knight. The rise in continuous wheat could see the disease worsen before the benefit of take-all decline kicks in, he warns.
Bigger cereal areas are bound to lead to earlier sowing as growers strive to avoid late-drilling penalties, adds Mr Knight.
"Earlier drilling is known to increase take-all risk in successive wheat crops."
What is more, growers could be underestimating current take-all levels, Mr Spink believes. Water and nutrient uptake is restricted long before the classic summer white-head symptoms show, he explains.
"There could be more take-all out there than we recognise."
The disease is present on nearly all farms, with conditions in 15 of the past 20 years putting 62% of UK winter wheats at medium or high risk, says Monsantos David Leaper.
One target of the HGCA/ Monsanto-funded research is to develop a computer model to assess yield loss risks and predict disease development at national, regional and even farm level.
Three key factors thought to affect take-all incidence are rotation, climate and soil type. The companys 1997 survey of 100 fields showed a good correlation between the first two.
Acidity and drainage can influence disease risk, adds Mr Leaper. But trials suggest soil type alone does not, merely determining attainable yield.
"Given the weight of data the percentage yield loss is nearly the same on a light, mid or heavy soil," he says.