Oilseed rape growers should budget for three or four fungicide sprays each season if they are to maximise yields from a crop which is coming under increasing disease pressure, according to UAP.

Speaking at a trials open day near Salisbury, Wiltshire, the firm’s Peter Gould said phoma, stem canker and sclerotinia incidence were increasing in many areas and growers could not afford to skimp on fungicides. “Many are probably using two or three fungicides, but really we should be treating rape more like wheat and using a three- to four-spray programme.” This would cost around £45-55/ha, he suggested.

Phoma and stem canker were the main threats and a trend towards minimum tillage, resulting in more trash being left on the soil surface, had contributed to increased phoma threat, he said. “If we ploughed all rape stubble, we probably wouldn’t see half the level of infection.” But in practice this was not possible in many situations, so a robust spray programme was vital, he said.

Even in varieties rated six for stem canker resistance (such as Castille), growers should plan to use two autumn fungicides, he advised. “You may get away with one in very dry years.”

UAP trials last year found that single green-bud applications of Sunorg Pro (metconazole) on large-canopied crops gave a 0.75t/ha yield response compared with untreated. “Use the green-bud input for PGR effects, which give a more compact canopy that is better able to intercept light.”

Metconazole has also been shown to improve rooting, especially when applied at the green-bud stage, he noted. “If you’re on shallow, drought-prone soils, this is pretty important.”

In terms of sclerotinia control, Mr Gould believed green-bud sprays would often let the disease in, so an early-mid flowering spray was a must – as highlighted by this year’s high disease incidence (Arable, 22 June). “Against sclerotinia, most products are preventative only. However, prothioconazole has 3-4 day kick-back, whereas Filan [boscalid] or Amistar [azoxystrobin] do not.”

Excellent control in trials had been achieved from half-rate metconazole followed by 0.6 litres/ha Prosaro (prothioconazole + tebuconazole). “Timing was critical. Sprays had to be on by mid-April, as soon as the crop hit the 15-20 pod stage.”