Do herbicide residues in manure/hay mulch affect trees?

I’ve been hearing more and more serious warnings and horror stories about vegetable gardeners/farmers and herbicides that can be applied to hay fields/pastures and carry over into the manure (as well as hay used for mulch.) I’ll copy a link below about what I’m talking about, but my question here is whether I should be concerned about these herbicides and fruit/nut trees, too, with manure I might use for fertilizer or hay I might use for mulch that comes from sources where I’m not completely sure about its herbicide history.


I think it is pretty specific to certain pesticides and certain types of veggies, at least in terms of the worst problems. Here is a good article:

It lists some of the crops most sensitive … no trees on there. There could be a smaller negative effect but doubtful it would be a horror story on trees.


Yeah, I haven’t ever seen trees listed as susceptible crops, but then I wondered if that’s because these issues are more likely to come up in a garden context (which I’m sure they would be) or because trees really aren’t particularly susceptible, which seems likely, too, but the cost of playing the odds could be really big if I lost.

Most hay crops , at least around here are not sprayed for weeds.
But …they certainly could be. Talking to the farmer would be the way to find out.
And yes, some of the herbicides listed above , especially picloram
( tordon ) can kill trees , and vegetables ,and persist in soil , compost ,hay , manure ,for years.
I have tried my best to buy hay out of the Same fields for years. I know the farmers, they don’t spray, and as importantly , I don’t bring home any weeds I don’t already have. Usually I scout the fields for weeds befor they cut, so I know what I am bringing home.
So… yes … caution is in order here. Ask if it has been sprayed ,!


I’ve been using wheat straw for chicken bedding from TSC. is wheat sprayed at all? i usually leave used bedding to compost a season before using it as fertilizer so hopefully any residue is leached out . i can easily go back to pine shavings.

Wheat here is sprayed at least once with broadleaf herbicide(s). Farmers will rotate a small grain in their fields so they can get glyphosate resistant weeds under control. They’ll go back to corn or soybeans after a year or two of small grains.

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Hillbillyhort is right: picloram can persist for years, and, I will add, will pass through animals when the hay is used for feed, so you can’t trust the manure either. Composting will not destroy it either.

But it will quickly affect any broadleaf plant, so it’s straightforward enough to do a bio assay by applying a bit to sensitive crops. Beans and tomatoes are good choices as they are particularly sensitive.


Yah. A bioassy , is a cheep, effective way to test.
Can be done indoors. In a flower pot, to test media before it would be time to spread compost for the season.

Wheat no doubt is spayed, but with what , and how persistent is it.?
Most likely, not very persistent if grown in a rotation with things like soy , sunflower, canola.etc. The farmer knows,but getting commodities 2nd or third hand , you will not know the history.

Wood chips ,may be a bigger threat. As these are usually from power line right of ways, precisely the areas where some of these more persistent -“ brush killers “ are used !
They want to kill the brush for awhile in these areas , so persistent
Herbicides are what they chose .
I think wood chips are a great resource, but again , caution is advised.


I can not see the residues being high enough to hurt trees. Picloram does stay in the soil for a long time but people spray pastures with trees all the time. As long as the spray does not drift onto the leaves I have never seen any damage. In fact if there are not enough leaves, spraying to kill trees will not be very effective. The take up from the soil is very minor. Velpar, on the other hand, does take up from the soil and I have seen that affect the soil for many years.

And dicamba is an ingredient in weed and feed lawn fertilizer. If there was a chance it could kill trees, they would not be able to sell it for lawn use.

Also, I did not see any reference to brush or trees in the articles. Trees are much more resistant to herbicides than tender seedlings.

Dicamba can indeed damage and kill trees

Milestone is a commonly used herbicides in pastures and on small grains where there’s a thistle problem. Milestone can and does damage and kill woody vegetation. I know this first hand :grimacing:

But that article seems to be talking more about drift than residue. Yes, it is a labeled for brush control. But that is at a higher rate than is applied to most hay fields.

The OP was talking about the small amount in hay residue, not direct spraying or the product washing off a field onto the neighbors field.