Thursday, September 9, 2010

Diatomaceous Earth and slugs... another efficacy experiment

As part of my War on Slugs, I stopped at a feed store to find out if they had Diatomaceous Earth, so that  I could test out the popularly held belief that DE will deter slugs away from food crops. All they had was a sample of a food grade version (sold as a flea repellent for dogs and cats). I  don't if using food grade versus regular DE would truly matter as a slug repellent, but the guy behind the counter was certain it would not, so I decided to bring it home and test it out.

Note that these are the same slugs that I used in my wood ash experiment.As you can see, I placed a tender lettuce seedling in the corner of this box and a large line of DE surrounding it.

This morning I opened the box. Not only was the lettuce seedling devoured, but the slugs crawled out of the box. Gross! I  found one, but the other one is missing. Ick. Guess I should probably leave my experiments outside, eh? Oh well, won't be the first  time I found a slug in the house (yes, there's that many slugs out here!).

So the question for me now is this: does it matter if it is food grade or not? Well, all the sellers on the internet seem to think not. I may do another experiment, but I doubt it works and it is expensive. Besides, there is some controversy over whether or not DE harms earthworms. I also wonder what affect the stuff would have on beneficial organisms and bacteria.

Can anyone out there shed further light on the issue?

For a list of all of my slug control experiments, please see this page.


Grace Peterson said...

Hi Amy Dear, Well, my theory is shot to hell, isn't it? I thought DE was cheap it's ground up shells, after all. It seems it was really cheap back in the day.

I hope that interloper slug shows up.

Neil K. said...

Is it possible the slugs avoided the DE and climbed the wall to get to the leaf?

Amy said...

Yes, it is possible. But I know that the slug at least touched the DE, as the DE had moved a little. I might do another experiment in the future, with non-food grade DE. But I don't think DE will be terribly effective in our climate, considering how much rain we accumulate in this climate. And when it isn't raining, the slugs aren't anywhere near as active.

Anonymous said...

The difference between food grade and pest grade is in the milling.

They may put some form of attractor in there as well, I have just put some down in the middle of the day and the slugs popped out for it.

Reports on pest control DE are very good in regards to killing insects with exoskeletons, so useful to have around, but it can kill bees as well.

I think it kills insects better when they ingest it, so had you put it on the leaf rather than just around the leaf you might have seen them die.

Supposedly it doesn't kill worms, and the digestive track of a slug is a spiral, whereas a worm's is straight.

I think DE is better used as an insecticide than as a deterrent, and if it really doesn't kill worms, then putting it in soil should work well.

For repellents then garlic tea sprayed on the leaves and stems of plants works quite well, they don't tend to touch garlic plants. But of course if there is no other food stuff available, they will probably just plod on through the garlic mist.