Fungicide for early flowers
OILSEED RAPE crops on farms with a history of sclerotinia or alternaria will almost certainly need treating with a flowering fungicide this season, suggests eastern counties TAG consultant Steve Baldock. Early drilled crops could require spraying imminently.
“Potential yield losses from disease attack are huge – we only need moderate responses to justify fungicide costs.”
Risk from sclerotinia attack rises if there is a previous history of infection, and as the intensity of oilseed rape increases in the rotation, he says. “Damp conditions around flowering is a critical factor.”
Where there is a history of infection, treatment should almost be routine, he says. “You can choose your armoury from treatments costing 3/ha to 25/ha.”
Coating petals before infection occurs is crucial, he stresses. “Make sure you use the right nozzle type. Flat-fans applying medium-fine sprays are good, or use angled nozzles or hollow cones if you have access to these. In reality a lot of growers use bubblejets, but these are not ideal as the spray hits the leaf rather than coating the petals.”
disease control Product choice should be aimed first and foremost at disease control, rather than attempting to get any physiological responses. “They”re a bonus.”
On high risk crops Amistar (azoxystrobin) or Filan (boscalid) are his top choices. “MBC will give slightly poorer results.”
Where sclerotinia risk is lower on fresh oilseed rape land, but there is potentially a higher yield potential, growers could consider using Amistar for its potential physiological benefits, he advises.
Rates on high yield potential sites will probably have to be at least 0.75 litres/ha this season, similar to those suggested by Syngenta, he suggests. “We don”t have the experience to say against that, as the rates required for physiological responses are still unproven in independent work.”
On lower yield potential sites, he suggests tank mixing in carbendazim (MBC) with 0.5 litres/ha Amistar to cheapen the mix. “That should give enough disease control.”
RAIN ONTO recently warmed soils raises the risk of sclerotinia in oilseed rape this season, confirms Syngenta”s Bruce McKenzie, who urges growers to consider the potential benefits of this year”s recommendation for Amistar (azoxystrobin) on the crop.
Two years ago only about 10% of winter rape needed treating against sclerotinia. Last season, because conditions favoured the disease, the figure was up to 40%, Mr McKenzie estimates. “This year could be a similar high spraying year.”
He highlights work over four seasons in Denmark, France and Germany and an ADAS trial in Kent last year.
The results show Amistar, which also controls alternaria, botrytis and gives strobilurin greening effects, offers a better margin over treatment cost than previous options including the other recently approved choice, prothioconazole (as in Proline).
Last year in Germany, where the infection level was especially high, it outyielded the triazole by 0.2t/ha (1.6cwt/acre) giving a 33/ha (13/acre) better margin, he notes.
Two applications per crop are permitted, but Mr McKenzie dismisses fears of sclerotinia strob-resistance developing. Unlike septoria the disease cycles only once a season, he explains. “The risk is very low.”
