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As a pre-emptive starting note, there are a lot of questions with similar titles but none I could find with pictures looking the same to what I have here.

Around a week ago, I applied lawn clippings to the surface of the soil in my greenhouse as a mulch. The soil was previously free of visible weeds or other pests and I'm aware that I may have made a mistake in introducing non composted grass clippings.

Today I noticed hundreds of small white balls that have appeared in several areas. They seem to be either eggs or some type of fungus. The fact that they appear to be "growing / deposited" on a plastic plant label makes me think that fungus is less likely, as I'm not sure that it would grow on a plastic.

In one picture a strawberry plant appears to be attacked.

  • What are these balls?
  • Are they harmful to my plants?
  • If so, how should I deal with them and what precautions can I take in the future?

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  • Not sure, looks like eggs of some kind. – Rob May 3 '19 at 14:07
  • There are a lot of what appears to be fruit flies in the greenhouse, but searching "fruit fly eggs" on google images, they don't look the same. – Karl May 3 '19 at 14:10
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How impressive!

I think you can relax - this is not a sign of a massive insect infestation and not a fungus, but one of nature’s wonders known as slime mold.

The “eggs” are the spore-carrying fruiting bodies. They come in lots of different shapes and colors, some with a striking resemblance to insect eggs. This one looks a bit like yours, for example. If you gently cut one open, you won’t find an insect embryo, just spores. In your last photo, you can also see the plasmodium, similar to a white “web” or “net” covering the lump of soil(?) next to the green plant’s center.

A precise id would probably require a specialist, but for you as a gardener, the most important parts are

  • they are part of the natural decaying and composting cycle (hello grass clippings)
  • they won’t damage your plants (although I would have the impulse to push them away from my seedlings)
  • it’s normal for them to “climb” on higher and drier spots when they create the fruiting bodies (like on the plastic label).

All in all, slime molds are pretty cool if you do some research, for example, they can actually move and oscillate and organize themselves.

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  • Great answer. I will leave them as they are then, as they are likely breaking down the grass clippings and releasing nutrients into the soil. – Karl May 3 '19 at 15:41

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