Theconsequence of not treating oilseed rape with a neonicotinoid insecticide seedtreatment is now becoming clearly apparent. Syngenta crop demonstration plotsat Rougham in Suffolk have shown a 40% reduction in plant survival on untreatedplots, compared to the same variety treated with Cruiser OSR.
Thecompanys Field Technical Manager, Simon Roberts, reported initial assessmentshad shown some limited visual impact of Flea Beetle shot-holing damage andearly Downy Mildew infection on seedlings. But, as the crop had developed, theeffects on crop vigour and plant survival had only now become truly apparent.
TheCruiser OSR protected plots have continued to establish well, with strongplants at four to six true leaves that are well set for the winter, at around85 to 90 plants per m2 he said. The adjacent untreated plots,however, typically now have just 50 plants/m2. Many of these plantsare smaller, and there is visibly greater insect pest damage on all theleaves.
Mr Robertsadded that this season had, so far, been reasonably favourable to oilseed rapeestablishment, which may have allowed more of the damaged and infected plantsto survive. If weather conditions had been a repeat of the extremely wet orvery dry seasons we have typically experienced in recent years, the situationfor the unprotected plants could have been far more serious, he warned.
Comparativetreated and untreated crops at the Syngenta Technical Innovation Centredemonstration sites across the UK will continue to be assessed through toharvest, to evaluate the full effect of the insect damage and disease infectionduring establishment. The smaller crop leaf area of untreated plants mayrequire additional costly fertiliser inputs to boost growth, and there is anincreased risk of yield loss from TuVY infection spread by aphid activity onuntreated plants.
Thelessons being learned will be invaluable to give growers guidance on how tomanage oilseed rape crop establishment without the protection of neonicotinoidseed treatments next autumn, advised Mr Roberts.
Phomalevels have increased dramatically over the past week, reported Simon Roberts.Oilseed rape crops at the Syngenta crop demonstration site in Suffolk that hadno infection at the end of October, were now in advanced stages that hadtriggered thresholds for Plover treatment.
Priorityshould be to treat small leaved crops, where infection could quickly spread tothe stems, he warned. Apply Plover at 0.25 l/ha where 10% plants are showingleaf spotting symptoms, followed up by a second treatment four to six weekslater if reinfection occurs.
Mr Robertsadvocated that where Phoma lesions were already present and developing quickly,the application rate of Plover should be increased to 0.5 l/ha, to enhancecurative and protectant activity.