Target disease early
By Mike Abram
TARGET EARLY season foliar disease clean-up sprays to specific varieties, drilling dates and disease risk, agronomists are urging.
“In regions where there is high disease pressure it is hard to argue against doing a T0 spray,” says Masstock technical manager Clare Bend. “Yield responses are consistently cost-effective.”
But where disease pressure is lower, such as in the east, T0 sprays should be targeted more at early drilled crops, and then according to varietal disease risk, advises UAP eastern region technical manager Brin Hughes. “Most varieties drilled by mid September will probably respond.”
One exception could be Robigus. “There”s probably a case for easing back on Robigus, unless you”re in a high risk yellow rust area such as The Wash, where a low dose of triazole might be advisable.”
Mrs Bend agrees Robigus is unlikely to respond in the east. “In our trials it didn”t respond at all in Essex last year, but in West Sussex where there was higher septoria pressure Robigus gave between 0.2 and 0.3t/ha extra yield.”
That is similar to the average yield response across all Masstock T0 trials in the past seven years. “Responses are higher on susceptible varieties – in 2004 it was up to 0.57t/ha.”
Reducing inoculum build-up early in the season is responsible for the yield boost, she believes. “Benefits in disease control can be seen right into July.”
Septoria levels on leaf 2 in July were 10% lower when a T0 had been applied in trials. “It is important to manage the disease before it manages you.”
Keeping disease in check now could also save money at T1, she suggests. “Unchecked foliar disease will probably increase costs at T1 through needing higher rates to get it under control. Responses to strobilurin fungicides are also more consistent when foliar disease is under control.”
Even reasonably resistant varieties, such as Claire, are worth treating if they are drilled early. “Claire drilled early behaves much more like Consort.”
But later sown crops may not need treating, unless they are racing away, says Mr Hughes.
Treat susceptible varieties with a combination of triazole and chlorothalonil, advises Yorkshire-based agronomist Paul Power. “Growers are taking a risk if they don”t treat disease-prone varieties. It buys time, particularly if you cannot get on with a traditional T1 because of the weather.”
A T0 will also avoid the temptation to go too early with a T1 spray, before leaf 3 emerges, notes Mrs Bend. “There”s always a temptation to get in before the weather breaks around T1. T0 sprays give some re-assurance if the weather does break.”