bacterial leaf spot (Pseudomonas)

Symptoms

Water-soaked spots starting at leaf edges, turning black/dark brown with a yellow halo, no fungal fuzz visible, spots may have a foul smell.

Plants affected

• Swiss cheese plant

Easily confused with

• overwatering / root rot risk

  How to tell them apart: Overwatering of Monstera deliciosa produces soft, dark brown-to-black mushy rot that starts at the oldest/lowest leaves and at the base, with the whole leaf or large sectors uniformly yellowing then collapsing; the soil stays soggy and roots turn brown and slimy. Pseudomonas cichorii bacterial leaf spot instead begins as discrete, angular-to-irregular water-soaked dark spots scattered on the leaf blade and margins, each often ringed by a bright yellow chlorotic halo, that enlarge and merge in warm wet conditions; spots are tied to wet foliage and overhead splashing rather than to soggy roots. Look at distribution and roots: diffuse basal collapse with rotten roots points to overwatering, while individual halo-edged spots on otherwise turgid leaves with healthy roots point to bacterial infection.

Common questions

How do I recognise bacterial leaf spot (Pseudomonas) on Swiss cheese plant?

Water-soaked spots starting at leaf edges, turning black/dark brown with a yellow halo, no fungal fuzz visible, spots may have a foul smell.

Do I have to report bacterial leaf spot (Pseudomonas)?

No. bacterial leaf spot (Pseudomonas) is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is bacterial leaf spot (Pseudomonas) 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.