Spotted Beets

[theduck7]

I work in a greenhouse where we grow edible vegetable shoots. One of the varieties we grow is beets and we have been having a problem with them. When they are two to three weeks old they start getting spots on the leaves. Our red beet shoots get brown spots on the leaves. The spots have are circular and there is an inner and outer ring. The outer ring is dark red and the inner one is brown. We also grow yellow beet shoots and on those the outer ring is brown and the inner ring is quite light colored. My boss thinks it's because their is mold in the dirt we buy. I'm hoping it's not that because we can't change our dirt.
Does anyone have an idea of what this could be and how we could treat it?

 

[Beth_B]

Do you have pictures?
I'd suspect fungus of some kind, especially if the spots start on the lower leaves and move up the plant.
Look up blight or cercospera leaf spot and see if those images match what you are seeing.

Not sure how you'd control that in a greenhouse environment. Most fungal diseases are caused or exacerbated by too much humidity and heat, overhead watering, watering late in the day, or like your boss said maybe trucked in with your soil. It can be tricky to battle once you've got it!