Black Spots on Spinach Leaves

[MoonShadows]

On Sunday afternoon while picking some spinach for salad, I found some small, what looked like, black bugs on the underside of some of the spinach leaves in my greenhouse. They seemed to be localized to one or two plants. I pulled the plants and disposed of them outside the greenhouse. Yesterday, I only found 1 leaf with a couple of those black "bugs". I picked it, and after looking at it through my 30x magnifying lens decided it is not a bug at all. I took a pin and easily opened it up. It was soft and black throughout. Not sure what it is. Any guesses?

Here's pic I found on the internet of it on a basil leaf.

Here's another one (ignore the powdery mildew in this picture)

[applestar]

From your description, I thought those must be the sporebearing body (mushroom) of the fungus that is already affecting the leaf.

I found a reference to it in this googlebook which I can’t access to copy the text, so I took a screenshot (attached below). I think the highlighted reference is regarding Pea mildew. There IS “spinach anthracnose” mentioned in the out of frame list, but I don’t think that is related.

Annual Report of the Ohio State Horticultural Society for the Year ... - Ohio State Horticultural Society - Google Books
https://books.google.com/books/about/An ... NQAQAAMAAJ

... here’s a more modern reference ...

Identification of Powdery Mildew Fungi
https://www.apsnet.org/edcenter/intropp ... ildew.aspx

At the end of the growing season, powdery mildew fungi produce sexual spores, known as ascospores, in a sac-like ascus (pl. asci) enclosed in a fruiting body called a chasmothecium (pl. chasmothecia) (cleistothecium is a former term for this structure that is still widely used). The chasmothecium is generally spherical with no natural opening


Epiphytic hyphae and chasmothecia on leaf surface. (Courtesy W. Gärtel)

[applestar]

...what do you use for fungal issues in the greenhouse?

[MoonShadows]

Let me see if I am understanding correctly ....you (and the reference) are saying these black dots are the spores that will produce powdery mildew?

I have a container of Bonide 811 Copper 4E Fungicide which will treat powdery mildew, but since I don't expect this crop of spinach to be around much longer (the greenhouse is going to be getting too warm for spinach). I may just pick any leaves I find it on unless it starts to spread from those isolated plants.

4025b8a6-3583-468c-b634-93c672d68109_1.8773d473fe4445bc70c5836837edc44a.jpg (25.76 KiB) Viewed 6632 times