Home gardening season has been officially started for several weeks now. Seeds and transplants have taken off and begun to grow tall and strong.
However, not all gardens are doing that well. Several folks have already brought in samples of tomato plants from their gardens that are stunted and curled. This condition is caused by unintended herbicide carryover.
Most of the herbicide damage I see in home gardens comes from the use of animal manure or hay mulch. Most gardeners don't give much thought to where their manure or hay comes from, but this is a big mistake. Today, the vast majority of pastures and hay fields are treated with herbicides which can remain active even after the animal eats and digests it.
While herbicides used today are much less toxic to humans and animals than in the past, they are able to remain active for several years after use. If livestock graze on a treated pasture, the herbicide can remain in the animal's manure for up to several years, even after composting! When you incorporate this manure into your soil, you have essentially contaminated your soil with the herbicide and hindered your garden's growth ability.
The same is true for gardeners who use hay for mulch. Some of the pasture herbicides can stay in the hay and leach into your garden soil. When you plant in the spring, your garden plants will take up some of the herbicide and either severely stunt or die altogether.
Herbicide damage is fairly easy to recognize once you've seen it for the first time. Tomato plants seem to be the most susceptible to herbicide carryover damage. Leaves will begin to curl under and appear misshapen. New growth will be severely stunted, and probably stop at some point.
If you see this damage on your garden plants and you have applied animal manure or hay to your garden, you are better off just pulling up the plants. It will be difficult to determine how long the herbicide will stay in your soil. It will eventually break down after a few years due to rainfall, sun exposure, and natural microbial breakdown. Your best bet is to move your garden to a different location next year. Some folks have even had to dig up their entire garden area and replace it with new soil just to be safe.
Using animal manure and natural mulches is a large part of the organic and sustainable gardening movement. If you are still interested in this practice, you will need to confirm as best you can that the manure or hay you use has not been treated with an herbicide known to carryover. The active ingredients in herbicides that are known to cause garden damage through carryover are aminopyralid, clorpyralid and picloram.
It can be difficult to truly confirm that manure or hay has not been exposed to these chemicals. Many times, livestock owners will unknowingly purchase hay that has been treated. They feed it to their livestock and then give you the free manure. It is tough in these cases to determine whose fault the garden damage is.
Now that you know of the potential dangers of using hay or manure, you can try your best to avoid unwanted damage to your vegetable garden.