spinach downy mildew

Symptoms

Yellow patches on upper leaf surfaces with corresponding grey-violet downy growth on undersides, severe infection causes leaf collapse + crop loss, baby leaf production (the main commercial format) particularly vulnerable, market quality lost even from light infection.

Plants affected

• spinach

Easily confused with

• bacterial leaf spot of spinach

  How to tell them apart: Peronospora effusa (spinach downy mildew) starts as pale, irregular chlorotic blotches on the upper leaf surface; the giveaway is a felty grey-violet sporulation that forms on the LOWER surface directly beneath those yellow patches in cool, humid, dewy conditions. Pseudomonas syringae pv. spinaciae (bacterial leaf spot) instead makes small, discrete, angular water-soaked spots that dry to tan-brown papery necrosis with a faint yellow halo, scattered between veins and often appearing greasy/translucent when held up to the light, with NO fuzzy growth underneath. If you flip the leaf and see downy mould, it is the oomycete; if the spots stay dry, sharp-edged and fungus-free, it is the bacterium.

Common questions

How do I recognise spinach downy mildew on spinach?

Yellow patches on upper leaf surfaces with corresponding grey-violet downy growth on undersides, severe infection causes leaf collapse + crop loss, baby leaf production (the main commercial format) particularly vulnerable, market quality lost even from light infection.

Do I have to report spinach downy mildew?

No. spinach downy mildew is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is spinach downy mildew treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.