Tomato plants owned by area gardener Andy Kippenhan. Kippenhan says the plants on the right were treated with contaminated manure from a local stable and died as a result of herbicide carryover. The plant in the photo to the left is a healthy tomato plant not treated with the contaminated manure.
Sure, you can smell it a mile away, but do you really know where your manure came from?
Gardeners know that the key to cultivating strong, healthy plants is good soil rich in nutrients. One of the ways gardeners achieve this is by adding manure to their compost or by applying it directly to garden beds. But local gardener Andy Kippenhan, who learned about the stinky side of manure the hard way, warns that farmers and gardeners should ask about the source before applying it to garden vegetable or flower beds.
Kippenhan said he incorporated horse manure from a local stable into soil that was used on his tomato plants, and that those plants died as a result of ‘herbicide carryover.’
Herbicide carryover happens when a grazing animal eats hay from a pasture that has been treated with an herbicide that does not break down in the digestive process. The herbicide remains in the manure at levels that can be deadly to certain plants, and can also remain active in hay, straw, grass and clippings.
After his plants died Kippenhan performed tests on other tomato plants to be sure manure from the local stable was the source of the problem. He used control plants with no treatment and other plants treated with both manure and hay from the stable. The treated plants began to shrivel within a matter of days.
Georgia House Representative Rick Jasperse, who served as Pickens County’s Extension Agent for nearly three decades, said he has written on the subject of herbicide carryover numerous times during his tenure with the extension office.
According to Jasperse, there is a group of relatively new herbicides used in pastures to control noxious weeds. He says these herbicides, which include the active ingredient picloram (commonly sold under the trade name Grazon and other generic names), are deadly to broadleaf plants, but not to plants in the grass family. This makes them perfect for use on a pasture for weed control, but makes them lethal on garden plants such as tomatoes and beans.
“Ten years ago this wasn’t an issue,” Jasperse said, “but we’d have pastures just taken over with weeds like pigweed and some of the thistles. Because of this new group of herbicides like Grazon, which is very widely used, we don’t have that problem anymore.”
But beyond being out several tomato plants, Kippenhan is frustrated about the use of chemicals such as Grazon, which he says corrupts the flow of nutrients in gardening and farming.
“Contaminating an entire nutrient cycle, making it dangerous to use, can never be a sustainable practice,” Kippenhan said. “Many people in this area and elsewhere produce fine hay of mixed species, without using a persistent herbicide, or even any at all.”
According to Jasperse, Grazon can be used only by licensed individuals and he says the package clearly states hay and manure should not be used on gardens. Still, he said, care is not always taken to communicate what herbicides have been used during hay production.
Jasperse said if the farmer who is providing the manure grows and cuts the hay on his or her own, it is easy for a gardener to find out if the animals were fed picloram-treated hay.
“But if the farmer gets the manure or hay from suppliers they may not know where that hay came from,” Jasperse said. “That’s what makes it hard. You don’t know where it comes from, and even the supplier may not know where the hay originally came from or what herbicide was used on it.”
Jasperse recommends hot composting all manure for one year to get rid of potentially harmful chemicals, “but honestly most people won’t do that,” he said. “There is a great publication in the Pickens Extension Office on how to create compost correctly.”
Jasperse said you can also test out the manure or hay on your own by applying it to a small part of your garden, but he recommends applying them to non-sensitive crops such as corn.
While Kippenhan said his tomato plants took just two days to show symptoms of contamination, Jasperse said the time the herbicide takes to affect the plant depends on the concentration of the chemical.
“If you add just a little manure to the soil and till it in one inch you might not have much impact,” Jasperse said, “but if you add five inches of manure and till it in you would have more possible damage.”
Here are some tips from the North Carolina Extension Service regarding ways herbicide carryover can be avoided.
For hay producers and dealers: Be sure you know if any herbicide used on your pasture can stay active in manure, and communicate that information to those who purchase the hay so you do not jeopardize their crops.
For livestock and horse owners: If you buy hay for your animals ask the seller which herbicides were used in producing the hay.
For farmers and gardeners wanting to use manure or compost: Before acquiring or using manure, ask what the animals were fed, the origin of the hay, and what, herbicides were used on the hay or pasture.
For farmers and gardeners wanting to use hay or grass clippings: Find out what herbicides were used in production of the hay or grass.