Part article taken from Farmers Weekly, April 2018, written by Agrovista agronomist Andy Steven.
There has been plenty to ponder on at the series of winter meetings this year. There are new products in the potato portfolio after years of little change, and there have been significant changes in the main disease of blight that growers have to deal with every season.
The latest results from samples taken by blight scouts have shown a significant shift in the UK population, with 3 7 _A2 increasing to now account for 24% of total blight.
The situation in Scotland is trickier, with no 3 7 _A2 found to date, but that is not to say it is not out there. With prevailing south-westerly winds, it's probably only a matter of time before it is detected.
To help us understand the changing population, growers and agronomists can sign up as blight scouts and submit samples from any infections they find in their crop.
Any information on risk is useful, whether from Blightwatch or other national risk assessments. As an aid to decision-making, we have found that in-field weather stations give much more accurate information on risks in local areas.
The shift in populations, coupled with the resistance issue and arrival of new chemistry, is leading us to have a major rethink on blight fungicide programmes.
For seed growers, some of the decisions are straightforward. Fluazinam is used under an extension of authorisation for minor use to help reduce powdery scab. When applied at planting, it can't then be used in the blight programme.
Where it hasn't been used in this situation the options are more complex. Used on its own, fluazinam will be inviting trouble further down the line, so it may see limited use in programmes along with good blight chemistry to use its effects on sclerotinia.
The new chemistry this season is Zorvec from DuPont. This offers a new mode of action, and it will have an important role to play in blight programmes, especially in the rapid-growth phase.
It will come in a pack with a partner product that will limit its use, as all partners have a seven-day interval recommendation while for Zorvec it is 10. It's important that we don't break the chemistry by overextending intervals and applying in blocks.
Programmes will be based on an early start at the rosette stage and alternating products throughout the season with the appropriate chemistry for the growth stage.
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