You ever heard the old saying “you can’t win for losing”? I feel that way quite often now days. I think the same thing can be said for home gardeners. If it isn’t dry weather, late freezes, insects, or plant diseases, it’s any of a number of other things that can damage plants in the home garden despite all the time and hard work that it takes to be a successful gardener. One additional potential problem is not one caused by an act of weather or other natural event but rather it is a problem that often times results from our own doing.
Already this year I have had a couple plant samples brought into my office (they happened to be tomatoes but could have been any number of garden vegetable plants). Each of the samples had twisted up limbs and very distorted new growth. These are very classic symptoms of herbicide damage. Once you see herbicide damage in vegetables, it is pretty obvious. In each case as I talked with the homeowner, we eliminated all the most common causes including spray drift, contaminated sprayers, etc. The one thing they had in common was the fact that they had used animal manures as an organic fertilizer. I have already seen accidental home garden herbicide damage to other crops as well including strawberries and I even had a rose sample brought in with very classic herbicide damage symptoms that resulted from a glyphosate product that was used to kill the weeds and grass growing around the rose bush.
I can never remember a time when there was so much interest in using organic fertilizers, etc. in the home garden. I’m not sure if it is the result of the extremely high price of nitrogen fertilizers or just the desire of home gardeners to get the added benefits of organic matter in their garden soil that has sparked the renewed interest in using organic fertilizers for home gardening.
Despite all the positive and very beneficial aspects of using such organic fertilizers, there is one potential drawback. That drawback is the potential for herbicide residue damage. Many of the common herbicides used to do broadleaf weed control in pastures, hayfields, and yes, even home lawns are often not broken down during the digestive process in grazing animals and can actually be passed along through manure and unknowingly incorporated into your garden or flower beds if these manures are used as fertilizers.
Even grass clippings from the home lawn can still contain enough 2,4-D and related products to cause damage if these products were applied to the home lawn.
Tomatoes, peppers, sweet potatoes, and many other vegetables grown in home gardens are very sensitive to these herbicides and can be damaged at incredibly small levels. They can be damaged at levels very much lower than other less sensitive plants.
The product 2,4-D is one of the most common of all broadleaf weed control products for both livestock producers as well as home lawn owners and can stay active in manures for a relatively short period of time, up to about three or four months or so. Other more active herbicides such as pichloram and several other products, sold in a number of pasture weed control products, is another story all together. Pichloram can stay active for a period of up to eighteen months in amounts that can damage tomatoes and other sensitive crops (remember it takes only a minute and almost immeasurably small amount).
Once damaged by herbicide there is very little a homeowner can do for the affected plants. Some will die outright, while others that do not receive a lethal dose will seldom if ever fruit properly. In my opinion, damaged plants should be replaced (in another location) whether they live or not. There is some research that indicates incorporating activated charcoal at about five pounds per 100 square feet to a depth of six inches can help to negate the harmful effects of possible soil herbicide residue. It is probably worth a try if this has happened to you; however, the best bet is to simply replace the plants and locate them in a different area.
There are a number of take home lessons to be learned. First and foremost is to carefully read and follow the labeled instructions of any weed control product used in and around the home landscape, pasture, hay field, etc. The use of organic (manure) fertilizers in the home garden certainly has benefits ( I certainly use them myself). Manures are a great source of nitrogen, phosphorous, and potassium (all vital plant nutrients) as well as much needed soil organic matter. If you are using such manure fertilizers, however, make sure that you know the source and make sure to find out if herbicides such as 2,4-D or pichloram have been used in and around those pastures – remember that is your responsibility to find out if such products were used when you get stable manure fertilizers and you are not sure about the source. If you use home compost, be careful not to use composted clippings from herbicide treated lawns in or around your vegetables, bedding plants, etc.
Finally, be very careful about using herbicide products around your garden and landscape. While herbicides can be necessary and very useful in taking care of broadleaf weed problems, they can have some very unintended results. Plants do not have to be directly sprayed to be damaged, as in the case of the manure. Herbicides can also drift, so absolutely avoid spraying on windy days. Many products such as 2,4-D can also volatize (turn to vapors and become airborne) especially on warm sunny days. Also make sure that you have (and label) a separate sprayer for herbicides apart from the sprayer you use for insecticides or fungicides. Herbicides are very difficult to clean out of sprayers, especially if you are spraying very sensitive plants such as vegetables.