Syngenta crop demonstration plots at Rougham in Suffolk have shown a 40% reduction in plant survival on untreated plots, compared to the same variety treated with CRUISER OSR.

The company’s Field Technical Manager, Simon Roberts, reported initial assessments had shown some limited visual impact of Flea Beetle shot-holing damage and early Downy Mildew infection on seedlings. But, as the crop had developed, the effects on crop vigour and plant survival had only now become truly apparent.         

The CRUISER OSR protected plots have continued to establish well, with strong plants at four to six true leaves that are well set for the winter, at around 85 to 90 plants per m²” he said. “The adjacent untreated plots, however, typically now have just 50 plants/m². Many of these plants are smaller, and there is visibly greater insect pest damage on all the leaves.”

Roberts added that this season had, so far, been reasonably favourable to oilseed rape establishment, which may have allowed more of the damaged and infected plants to survive. “If weather conditions had been a repeat of the extremely wet or very dry seasons we have typically experienced in recent years, the situation for the unprotected plants could have been far more serious,” he warned.

Comparative treated and untreated crops at the Syngenta Technical Innovation Centre demonstration sites across the UK will continue to be assessed through to harvest, to evaluate the full effect of the insect damage and disease infection during establishment. The smaller crop leaf area of untreated plants may require additional costly fertiliser inputs to boost growth, and there is an increased risk of yield loss from TuYVinfection spread by aphid activity on untreated plants.

“The lessons being learned will be invaluable to give growers guidance on how to manage oilseed rape crop establishment without the protection of neonicotinoid seed treatments next autumn,” advised Mr Roberts.

Phoma explosion

Phoma levels have increased dramatically over the past week, reported Simon Roberts. Oilseed rape crops at the Syngenta crop demonstration site in Suffolk that had no infection at the end of October, were now in advanced stages that had triggered thresholds for PLOVER treatment.

“Priority should be to treat small leaved crops, where infection could quickly spread to the stems,” he warned. “Apply PLOVER at 0.25 l/ha where 10% plants are showing leaf spotting symptoms, followed up by a second treatment four to six weeks later if reinfection occurs.”

Mr Roberts advocated that where Phoma lesions were already present and developing quickly, the application rate of PLOVER should be increased to 0.5 l/ha, to enhance curative and protectant activity.