Onions - Acrobat

Onions

The most serious foliage disease in onions is downy mildew (Peronospora destructor) which favours cool/warm, humid or wet conditions. Outbreaks commonly occur in response to cool, overcast, moist conditions when the relative humidity during pre-dawn hours is greater than 95%, with 3 to 5 hours of leaf wetness and overnight temperatures of between 4ºC and 24ºC. Optimum temperatures are between 10ºC and 13ºC. Spores are produced on foliage overnight and released during the morning. These spores can survive for 1 to 3 days and are spread by wind and rain splash.

Downy mildew first appears on the leaves as pale green, elongated patches, which develop a greyish-violet, furry growth containing spores and spore-producing structures.

Application timing

Acrobat SC works at numerous points in the fungal life cycle, providing effective protection against downy mildew, and should be applied with Penncozeb 750DF (mancozeb) as a protectant treatment before the downy mildew infection occurs.

Downy mildew on onions

This information is also available in the Acrobat SC Technical Manual.

Download pages here.

KARL RIEDEL
Consultant,
Campbell's Horticultural Consulting

Karl provides agronomic advice and services to various growers, including one of the largest fresh market onion producers in Victoria. Controlling downy mildew in lettuce and onions is a problem that he helps them to tackle every year.

"Downy mildew can be a problem in lettuce and onion crops, and requires a strategic approach dependant on the level of disease," Karl explained.

"Most of our guys use Acrobat as tactical component of their disease control plans. It forms the backbone of their programs and has been one of the mainstays. One of my growers refers to it as the Rolls Royce product for downy mildew control, keeping it on the shelf to tackle the problem.

"We tend to treat the crop with preventatives first and then something like Ridomil. We use Acrobat to help protect against the development of resistance, especially in onions.

"Growers apply Acrobat in a block of two sprays. It has an excellent strategic fit with their disease management programs and works well."

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