What's causing small black dots and holes in the leaves of my potted vegetable plants?

Question

We planted a bunch of vegetables in different pots for the first time this year. We haven't used any pesticides or fertilizers on them.

We've been noticing little black dots on the pots we planted them in, and on the plants themselves. So far we've only noticed the dots on the yellow squash, zucchini, and cauliflower, but they're also on all of the pots.

The plant leaves also have a bunch of holes in them, and we're not sure if that's normal or not. There are lots of gnat-type bugs flying around the garden all the time.

Can anyone fill us in on what's going on, and how to stop these issues if they're harmful?

Answer 1

Those little black dots are Arterial Fungus. My guess is that you have wood chip mulch near by. The mulch shoots out spores which are especially attracted to light colored objects. Anyone who has light colored vinyl siding house with mulch at the ground level in there flower bed will have these dots all the way up their siding and to their eves trough. The fungus releases in cooler weather, around 55-60F degrees. The fungus is a little hard to take off because after you chip the black dot like pimple off there is a sticky residue underneath that needs to be cleaned. If it becomes a problem I suggest you eliminate the wood mulch and go with another alternative available in your region. Arterial Fungus usually occurs on the east coast of the US. Good luck. Gardner Wayne

Answer 2

Have you checked for caterpillars? Something is eating the leaves and it has a certain size, judging by the eating pattern. Could also be slugs, but then you would have noticed slime traces which I didn't see on the pictures.

A healty plant can compensate for some loss, but if this continues, they might be bare in a few days or weeks, and that would nix your harvest.

So take one pot at the time and search for "uninvited tennants". Note that some caterpillars are camouflaged quite well - we had one turnip¹ on our balcony one year and one caterpillar. Took us two weeks until we found it and we lost most leaves in the process. Pick them off by hand, this is certainly not a case for pesticides.

I suppose the black dots are caterpillar droppings, but couldn't say for sure as the photos are a bit blurry. Just hose them off, pick the caterpillars and ask again if they reappear.

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¹ That was a fun project for the kids, not an attempt to get an actual "harvest". We choose to let the caterpillar grow until pupation as neither kid was too keen on eating the turnip anyway. Sometimes you have to be flexible...