The off-label approval comes in time to help tackle the disease in this year's downy mildew fungicide programmes, which kick off this month.
Certis technical officer Alan Horgan said: "It is particularly advantageous given the increasing disease pressures following this recent warm showery weather that is ideal for spreading infection."
The SOLA has been granted following Valbon's re-registration, as part of the ongoing EU pesticide review process, continuing growers' access to an effective fungicide against downy mildew.
Horgan added: "The changes to the off-label for Valbon means growers have to focus their minds and consider carefully its use within a programme. In onion crops in particular - programmes run from June on-wards every week - with anything from six to nine sprays being applied depending on the season as it develops."
Growers can apply up to three sprays of Valbon. It contains the active ingredients benthiavalicarb and mancozeb. The sprays should be spaced out - such as one spray a fortnight and the use of the product should be alternated with other chemistry.
The benthiavalicarb component of Valbon belongs to the carboxylic acid amide (CAA) group of fungicides. Horgan said: "No more than half of the total number of sprays applied to the crop should consist of CAA fungicides.
"For outdoor bulb onion, shallot and garlic crops the maximum individual dose is 1.6kg/ha.
Growers can make three applications per crop providing the maximum total dose of 4.8kg/ha/crop isn't exceeded and providing a 28-day harvest interval is observed."
Application can be made in a minimum of 200 litres of water per hectare by conventional hydraulic sprayers including air-assisted hydraulic sprayers and handheld sprayers.