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.

Early drilling
  • Drilling oilseed rape earlier could help crops better resist phoma infection and ultimately improve yield, Mr Gould said. “Rape is very good at taking up nitrogen in autumn and winter, so if you drill it earlier, eg. 15-20 August, it will trap more nitrogen. Thicker, stronger stems are better able to withstand infection.”

    But seed rates should be reduced to 50-60 seeds/sq m when crops were drilled early, compared with 70-80 seeds/sq m for those sown in early September, he suggested.

    Varieties such as ES Astrid, Castille and Recommended List candidate, Komando, were suited to early drilling, he said. “Komando is well worth watching. It’s got Castille-type biomass and gross output, good stem stiffness and is rated eight against canker. Autumn vigour is a bit suspect though, so drill it early to get it up and running.”

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.”



Seed treatments
  • Seed treatments were an important part of Mr Gould’s armoury, particularly in the fight against phoma. “Many people could be underestimating the amount of phoma carried over on seed.” Trials found that HY-PRO Duet (prochloraz/thiram) reduced and delayed the incidence of phoma compared with untreated plots.

    “Hopefully by autumn 2008, we will have a new Bayer material – clothianidin. It is more persistent and active, which has been reflected in overall crop vigour.”

    He also urged growers to consider treatments with activity against turnip yellows virus (formerly beet western yellows virus). “In some trials we’ve seen up to 90% plants infected and 15-20% yield loss. Chinook [beta-cyfluthrin + imidacloprid] has some effect, but Deter [clothianidin] appears to be longer-lasting.”

    The disease was transmitted by aphids and he advised growers to treat crops with an insecticide as soon as numbers of Myzus persicae aphids built up.

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.”

Pellet rape seed
  • Pelleted oilseed rape seed could improve crop establishment and make handling seed safer for growers, according to Monsanto. The firm is trialling a new clay pellet, which is based on a similar principle to pelleted sugar beet seed. “Being hydrophilic, it draws water towards the seed, aiding establishment,” said Monsanto’s Robert Plaice. The technology is not commercially available yet, but if trials are successful, there may be scope to treat seed before applying the clay pellet, which would reduce operator exposure to the chemical seed treatment, he noted.

paul.spackman@rbi.co.uk