Know your onion SOLAS

Without the current range of Specific Off-Label Approvals (SOLAs) now available for onions, UK growers would not be in a position to grow this crop, according to specialist agronomist Andy Richardson. He says that at least half of all products used on onions are applied using a SOLA and he is convinced that this type of recommendation is vital for the wide array of minor crops, usually vegetables, grown in the UK.

"There are 9,000 hectares of onions grown in the UK, so it is a reasonable sized crop. We rely on SOLAs to make sure that our growers can produce the high quality produce that consumers expect. For example white rot control is virtually reliant on two fungicides, Signum and tebuconazole, both of which have SOLAs for its control. There are no label recommendations against white rot in onions, which is a very serious disease in this crop and can reduce yields and marketability."

"In order to keep this damaging soil borne disease at bay, we need a comprehensive programme of fungicide sprays, two Signum and two tebuconazole. I would recommend Signum as the first spray, particularly if the crop is struggling, as it has positive growth benefits whereas tebuconazole can act as a growth regulator. It is important to alternate these two fungicides as they have different modes of action and already there are some reported instances of resistance to tebuconazole in other countries," he warns.

Andy explains that white rot is a severe disease on those farms that suffer from it. "It is soil borne and its sclerotia can remain active in the soil for over thirty years. When the soil temperature is right, around 10° C, usually the start of May, the sclerotia germinate in response to root exudates from an Allium plant. Once in the soil it will always be a problem to onions and other Alliums such as garlic and shallots."

When it comes to downy mildew in onions, Andy explains that there are a few more options but still a relatively restricted list, bearing in mind the number of fungicide applications that are normally applied. "Invader is the backbone of any downy mildew programme in onions and would be integrated with other actives such as straight mancozeb, chlorothalonil, azoxystrobin, metalaxyl-m plus chlorothalonil and benthiavalicarb plus mancozeb. The fact that Invader has a 7 day harvest interval in its SOLA is very useful, as other fungicides have much longer, 28 days, and the crop does need to be protected close to harvest."

"Downy mildew can be a really serious foliar disease in onions, with some growers spending over £300/ha protecting against it. It is particularly a problem when it is warm, wet and humid - in fact the exact same conditions in which potato blight thrives. A comprehensive fungicide programme of around 7-8 sprays is often required in onions and so we will continue to need a range of products with different modes of action from which to choose," Andy Richardson concludes.

For further comment and information please contact Andy Richardson on 07860 558143 (mobile)