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elizabethlouise21

Herbicide carryover in straw mulch! Help!

Elizabethlouise21
10 years ago

Hi there.

This year I contacted my neighbor regarding a pile of old, rotting straw I'd seen laying around his place. He gave me 2 bales which I used to mulch my garden. Now my tomatoes, in particular, are showing signs if herbicide damage. The leaves are elongated, very curled (especially new top growth), twisted and the plants overall appear stunted. The other plants in the mulched area are not doing as well as I'd expect but most are doing better than the tomatoes. The onion, zucchini and cabbage seem to be doing the best while the tomatoes, peppers and beans are struggling.

My question is whether I should remove the mulch or leave it? It's been down now for at least 8 weeks so I'm sure it's well into the soil. At this point, I think it's too late to replant so this year may just be a bust. But in terms of overall longevity, would removing the mulch help? Would it help for this years already damaged plants? Should I just leave it in place and let nature sort it out?

The straw had been sitting untouched for years. How long will herbicides remain viable? I'm not sure what particular herbicide it might be, but based on my research an herbicide seems the culprit.

Any advice is greatly appreciated.

Thank you!!!!

Elizabeth

Comments (5)

  • elisa_z5
    10 years ago

    Such a shame. You're describing exactly the pattern of which crops are most affected by that very persistant herbicide which one of the scientists will soon come on here and identify.

    From what I've seen in previous posts, you'd do best to remove all the mulch asap, as even though some crops are doing okay, you'll need to rotate the more susceptible crops into those areas in future years.

    I'm sure one of the more knowledgeable folks will comment and give you more info.

    So sorry this happened. For mulch I always stick to hay--and that from fields I know are not sprayed--instead of straw. I know it's got weed seeds, but that's a lot better than herbicide damage.

  • digdirt2
    10 years ago

    PCA (pyridine-carboxylic acids) herbicides (aka persistant herbicides) can remain active for several months up to 3 or more years. They were developed to be that way. That makes them highly resistant to any biological decomposition process even in highly active and well maintained compost operations.

    A straw bale is very slow to decompose, even when exposed to weather, because it is 95% carbon so any PCAs in it can easily last for years.

    Many plants and grasses can tolerate it but most garden vegetables are very susceptible to it.

    Most common PCAs are Clopyralid, Aminopyralid, and Picloram.

    Remove all the contaminated mulch from the garden ASAP and hope for the best this year. Before future use flooding the garden area is supposed to help as the higher the soil moisture content the faster the chemical breakdown.

    Sorry for your problems especially when your original intentions - mulching - were so good.

    Dave

    Here is a link that might be useful: Clopyralid and Other Pesticides Info Sheet

  • theforgottenone1013 (SE MI zone 5b/6a)
    10 years ago

    Are you sure it's the straw causing the problems? If the plants are just now showing signs of damage and the straw has been down for 8 weeks it sort of makes me wonder if the straw is the actual problem here. It especially makes me wonder because the zucchini is also mulched and it is one of the plants doing the best. Cucurbits are rather tender when it comes to insecticides and herbicides. Have the plants been doing poorly since the beginning?

    Rodney

  • tishtoshnm Zone 6/NM
    10 years ago

    I would absolutely remove the mulch. One year I went to a friend's house to harvest some free horse manure. That manure was contaminated with herbicide. Of course, I did not know this before incorporating it into my garden. The 3 families that seem to be most susceptible are legumes, nightshades and the spinach family (I forget what it is called). I second Dave's advice of trying to flush it out and I would also recommend amending with lots of compost too. For next season, to do a quick test to see if it is still active, plant peas. If the plants look deformed, you know not to plant any of the susceptible families there. For some of our plants, once they pushed through the zone of contamination, they began to recover, slightly. It has been 3 years now and I think that next season most of the locations will be ready for nightshades again. Good luck.

  • digdirt2
    10 years ago

    Rodney raises a good point. Are you absolutely sure the cause is the mulch rather than just drift from a nearby application?

    Dave