Anyone know about safety of rodent-cides use in orchards/gardens

In an attempt to keep the gopher and vole populations in check I have been using various baits for many years. Mostly warfin-like anti-coagulants and some strychnine and zinc phosphide based ones. They seem to work fairly well in keeping these rodent populations under control, but my wife recently asked a good question, to what extent should we be worried about these poisons being taken up into the fruits and vegetables we are growing?

I have not seen any studies which address this. I am curious if anyone on the forum has seen any studies talk about this or know anything about this question.

Not an expert, but generally speaking plants are pretty picky about what chemicals they take up through their roots. So long as there’s no heavy metals I wouldn’t think to be concerned. But again, just speculating.

The plant won’t take up those chemicals until they are broken down by soil bacteria. At that point they won’t be a poison anymore.


While we are on this topic, I was wondering how safe is Milorganite on fruits and veggies? The maker of Milorganite said it safe but I have read some where on GW that said never to use on fruits for some safety reasons. It sure make the grass real green for a long time but I had too many fruit trees on the lawn.


" Vegetables and Fruit test,
For decades, gardeners have reported that Milorganite has helped them to grow the biggest and tastiest tomatoes, the most succulent strawberries, and the crunchiest carrots. Milorganite can help you get the biggest haul of your favorite fruits and vegetables.

Milorganite’s slow-release organic nitrogen formula feeds plants evenly and gradually. This nurtures the roots, which in turn develop more robust stems and leaves. Other fertilizers force unnecessary top growth, which makes for skinny plants with reduced yields.

Apply at the proper rates and watch how Milorganite provides abundant nutrition, growing strong roots and great yields. Milorganite is safe to use in vegetable gardens, and complies with the most stringent EPA requirements. For additional information on Milorganite’s safety visit our Safety."

Does any product ever claim that it complies with the most lax requirements? :slightly_smiling:


Tony, Years ago we tested Milorganite for heavy metals in Colo. Came up strong in Cadnium especially. I’ve been told exhaustively here and other places that that is not the case any more. Ok, I can believe that w/ the gov’t regs, I still can’t get past using human waste on veggie gardens, just me.

It’s worth questioning. Heavy metals concentrations are bad enough, but I also wonder about discarded/excreted drugs. I always assumed that those things broke down over time or during composting, but is it true?

I know that some leaf assay work is done by geologists in hopes of finding certain metals, so some things apparently do get picked up by plants.

Mark, you just caused me to spend the largest part of my evening reading articles on phytoremediation of organic contaminants. That was not way I’d planned to spend the evening.


In my opinion: Azomite, Milorganite, and Rock Dust are just clever ways of getting U.S. consumers to bury unwanted by-products in their gardens.If you want details I’d be happy to oblige.

On the subject of “safety of rodent-cides use in orchards/gardens”, I whole-heartedly agree with @fruitnut that “The plant won’t take up those chemicals until they are broken down by soil bacteria. At that point they won’t be a poison anymore.” Further, for those rodent-cides approved for sale in California the risk of secondary kill is low. This refers to the fate of critters that eat the dead (poisoned) rodent. Very sadly the rodent-cides in California with the least risks are only available to licensed applicators (myself included) and those sold in stores are of what I’d term moderate risk. If you’re concerned about outcomes I’d recommend using enclosed bait stations that (1) won’t be used by rodent predators or pets, and (2) are likely to keep the rodent contained after ingestion.

I used to work for a city government that sold the “solids” that came out of the sewer treatment plant/process. Farmers would fight to get that stuff and absolutely loved it. The regulations said that it could only be used on non-food crops (hay, etc) but I know for certain that many of them did use it on food crops. The really disgusting thing about it (and forgive me for this) is that once it was applied, after it rained you could see feminine hygiene plastic parts and prophylactics everywhere. How would you like eating tomatoes fertilized with those items?

Knowing the bio-chemistry, I wouldn’t care. But fundamentally, it’s disgusting! I would actually be more concerned about other high-density substances in the outflow.

That reminds me- we had a company that was trying to get us to hire them build us a new sewer treatment plant using a new technology. We went to tour a plant out of state that they had built, and at the end of the tour the salesman took a glass and held it in the water that was coming directly out of the sewer plant. He told us it was cleaner than the water in our tap, and took a big drink of it! Maybe it did test cleaner, but in my mind it was still just purified sewage! haha. I know it was just a mental thing, but it was pretty shocking! No thanks!

Toilet-to-tap is still a big issue in the U.S. It is interesting that the the process of sea-water reclamation is accepted because there are more “threats” in that source than sewage.

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I wish I knew the details of what plants will or won’t pick up from the soil more. I can be somewhat complex. For example, iodine. The plant has no use for it, yet it will uptake it if it is available. When people lived on land deficient in iodine they got goiter (like the goiter belt in the midwest a while back) until we started adding iodine to salt.

Now most of these compounds are quite a bit different than iodine, but some like cyanide are used in plants (apple and pear seeds skin have some), and I’d be curious if the plant had some way to accumulate it, for example.

Heavy metals are a concern, since quite a few of them seem to find their way into plants if they are in high concentrations in the soil. Not directly related to rodent-cides, but an example of bio accumulation.

Again not to say these rodent-cides will act in the same way, but in theory they could. It would be nice if there were some studies on it.

There are many.

Sorry about that! But, as long as you did, would you care to share what your take-away is?

I read this while trying to eat breakfast. Reminds me of a time…

And bio-accumulation can be tricky. Kale (and it’s relatives) are hyper-accumulators. They suck heavy metals out of the soil. If grown on contaminated ground, they do a great job of bio-remediating the soil, but then people are eating the contaminants.

I have used several rodent-cides around the orchard. We had good luck locating the runs and tunnels along the fence just outside of the orchard and placing the material in that location rather than putting the material adjacent to the trees. I’m not sure about the ability of the soil to absorb the chemicals long term. Zink phosphide is converted to phosphine gas by moisture or stomach acid and there is no antidote.

Apologies back to you, Mark. The reason I didn’t just share outright last night was because I didn’t want to come across as pretending to know more than I do.

What I found was articles on the use of particular plants to uptake and sequester heavy metals. Sunflowers and the mustard family are mentioned particularly often for pulling them out of soils - willows and poplars for cleaning contaminated water. Plants that store those contaminants in their stems can be harvested to have the metals extracted. I found it interesting that crops of maize and canola are being used in South America to clean up fields contaminated by gold mining, and that the metals, including gold are being extracted from their stalks.

Plants and bacteria are used to break down petroleum products and other organic chemicals so that they are non-hazardous and/or useful in the environment. Of note is that I did not find anything saying that pharmaceuticals and other complex molecules were being taken up and stored in plant material. So, I can’t say that there is no problem with them. Only that I suspect that if it were, it would have been both newsworthy and studyworthy enough to be publicized to the extent that it would be not be so difficult for even a bumbler like me to find.

Specifically pertaining to rodenticides, I found this Human and Environmental Exposure to Rotenticides in Google books. It evaluates the effects on rodents, other animals, secondary ingestors,and worst case scenarios on the soil, air, water, breakdown and remaining percentage in treated sewage products, of the rodenticides used in Norway. Applicable information and analysis begins on page 44 or 45 and extends into the 70’s. That’s where I stopped gleaning and gave my brain a rest.

I didn’t mean to leave you hanging, but few hours of delving into the subject doesn’t make me an authority on that area of botany.