7 June 2002

Triple treatments now needed in wheat crops

By Andrew Blake

MORE winter wheats than usual could merit a third fungicide treatment after an especially tricky spraying season.

With initial inputs eased because of low disease pressure, and the T1-T2 interval uncomfortably stretched by bad weather, potentially high yielding crops now need every protection, say specialists.

Stands may appear clean, but recent wet weather could lead to a septoria "explosion" in poorly protected fields, warns Masstocks Malcolm Smith.

Yellow rust has already hit several untreated varieties, highlighting the threat from a disease no longer confined to the east, says Hutchinsons Dick Neale.

Septoria is on leaf 2 in untreated Claire and after 150mm (6in) of rain in May many T2 treatments need topping up, adds UAPs Peter Gould.

In parts of the west, where weather has hit spraying hardest, combining T2 flag-leaf sprays with a T3 ear wash may have to be considered. But that is a compromise best avoided, says Mr Smith.

The timing to cure septoria and provide protection against other diseases is unlikely to coincide with the optimum for fusarium, he explains. Yields increase 0.15t/ha for every day green leaf area can be preserved, so keeping septoria and other foliar diseases under control is the main aim.

Only in the worst case scenario, where nothing has been applied since T1, would the kick-back of a pyraclostrobin-based treatment including Tucana or Opera be merited, he adds.

Fusarium aside, the key in deciding what to apply at T3 is how much septoria eradicant was used at T2, says Mr Neale. "A lot of Twist (trifloxystrobin) has gone on. Its a very good protectant but offers only about two days eradication."

His other concern is that many growers applying Opera (pyraclostrobin + epoxiconazole) may have used less than robust doses to economise. "The minimum should have been 0.75 litres/ha or half rate. But often people have been down to 0.5 litres."

With sub-standard grain likely to be hard to market this harvest Richard Cartwright of Chichester Crop Consultancy believes a T3 to control fusarium will be well worthwhile and not just on quality wheats like Malacca. Some feed varieties could benefit too.

His choice is an Amistar (azoxystrobin)/tebuconazole mix. "Rates will depend on what you have used before and what you are trying to achieve. But economising much below 0.25 litres/ha of each is hard to justify."

Where the target is specifically fusarium, say on susceptible varieties like Xi19 and Charger, growers only recently applying a T2 must be prepared to go again soon – at early flowering – for best control, says ADASs David Parish.

"Folicur (tebuconazole) at 0.5 litres/ha is a fairly robust treatment. And at a cost of £1/t for an 8t/ha crop it is a prudent investment even with grain at only £55/t." &#42

WHEAT T3 SPRAYS

&#8226 More rewarding then usual.

&#8226 Septoria ready to "explode".

&#8226 T2 top-ups often required.

&#8226 Fusarium a rising concern.

Wind and rain-delayed flag-leaf fungicides mean triple spraying looks unavoidable for many, say crop experts.

&#8226 More rewarding then usual.

&#8226 Septoria ready to "explode".

&#8226 T2 top-ups often required.

&#8226 Fusarium a rising concern.