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Even with care, some herbicide use can hurt

Posted: June 18, 2017 - 12:03am
Tomatoes are highly sensitive plants, and are not spared by broadleaf herbicide chemicals. Weed control must be performed with care, as even light exposure to products like glyphosate (Roundup) – sometimes as a consequence of the wind carrying excess chemical from other sites – can cause damage.

Home gardening season has been officially begun in the CSRA. Seeds and transplants have grown tall and strong.

However, not all gardens are doing that well. Several clients have brought in samples of tomato plants from their gardens that are stunted, curled and have yellow discoloration near the base of the leaves. These conditions are caused by unintended herbicide carryover or unintentional herbicide drift. Most gardeners don't give much thought to where their manure or hay mulches come from, but this is a big mistake.

Another big mistake is making selective and nonselective herbicide applications near the garden during high temperatures or during windy conditions. Both of these can lead to damage and death of the tomato plants in your garden. Using animal manure and natural mulches is a large part of the organic and sustainable gardening movement. If you currently use these practices, you will need to confirm 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.

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.

If you do not use the above applications in your garden, unintentional herbicide drift could be the culprit. Tomatoes are very sensitive to injury from broadleaf herbicide chemicals. Even light exposures can result in injury to the plants. If an herbicide like glyphosate (Roundup) or a product containing 2,4-D or dicamba is applied in the vicinity of a vegetable garden, it can easily drift onto the plants. The most common injury symptoms observed are caused by phenoxy herbicides such as 2,4-D and dicamba. These are commonly used for controlling weeds like dandelions, plantain and clover in home lawns. These chemicals are growth regulator, hormone-type weed control chemicals. Tomato plants usually come in contact with the chemical through spray drift or the use of a sprayer that was previously used to apply the herbicide. It is also possible to expose tomato plants to broadleaf herbicides by using grass clippings from lawns recently treated for these weeds as mulch in the vegetable garden. Be sure to follow any and all herbicide label directions regarding the use of treated grass clippings for mulches in vegetable gardens. Glyphosate (Roundup) is another herbicide that has the potential to damage the vegetable garden. This is a non-selective herbicide used in many landscape applications to control unwanted weeds in natural areas or beds.

The most distinct and recognizable symptom of glyphosate damage is bleaching at the base of leaflets. Upward cupping of leaflets, browning of the leaflet edges and deformed fruit with dark brown scarring are also common.

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 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, you are better off just pulling up the plants.

Now that you know of the potential dangers of using hay, manure and herbicides around the garden, you can try your best to avoid unwanted damage to your vegetable garden.

 

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