With OSR going into the ground at the beginning of August in many areas there was always the possibility that Phoma thresholds could be reached early, and that has proved to be the case.
ADAS monitor rain events at their regional centres and by the end of September many were getting close to the 20-day rain event threshold. Of those, ADAS High Mowthorpe, near Malton North Yorkshire, was closest with 18 rain days but many others are not far behind.
ADAS plant pathologist Philip Walker wants growers to be vigilant and check crops for the first signs of the disease, especially as autumn temperatures have been quite warm. “Typically, 20 days with rain is sufficient to cause spore release from stubbles, and this will be reached in many areas soon. Also, the early autumn weather has been reasonably warm, which favours disease development as it requires around 120-degree days for leaf spotting to appear following initial infection,” he notes.
The particular risk for him is small plants, for example, those that haven’t established well. The smaller the plant the easier it is for stem cankers to form he warns. “The disease spreads from the lesion, through the leaf and leaf petiole, then into the stem, forming cankers which can result in yield loss. Once the disease has reached the stem it is beyond the reach of fungicides, hence why monitoring for leaf spotting thresholds and timing of application is important. Smaller crops may benefit from fungicides being applied at 10% plants affected instead of delaying until 20% of plants have leaf spotting,” he adds.
Spot check service
One option for those wanting further disease insight is through the Bayer/ADAS SpotCheck service – now in its 7th season of operation. Again, farmers and agronomists will have the opportunity to send leaves in for testing for Phoma, Light Leaf Spot (LLS) and powdery and downy mildew infection. As before the service is free of charge and runs from October into the spring of 2023.
Project lead Richard Williams feels the service is useful to confirm the presence of OSR disease threats, but particularly valuable where LLS is suspected. “LLS can be a very tricky disease to see in a field. It is often patchy and the ‘salt grain’ spots hard to see, especially when leaf surfaces are wet,” he warns.
He sees the SpotCheck service as a support tool to help with disease control decisions, important as timing is key with limited curative fungicide activity. “Aviator (prothioconazole + bixafen) is the most effective fungicide option, but even this will not fully eradicate established disease,” he adds.
For those wanting to take advantage of the service, they are advised to contact their local Bayer commercial technical manager.
