Systemic Pesticides: Chemicals You Can’t Wash Off

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Systemic pesticides are in the plant, not on it. When we make the plant itself poisonous to predators, one has to wonder what (or who) else it’s poisoning.
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A garden seed company recently sent us these seeds for a new sweet corn. The seeds were treated with Cruiser, which is thiamethoxam, a systemic neonicotinoid insecticide. They were also treated with four fungicides: azoxystrobin, carboxin, fludioxonil and mefenoxam!

In conventional food production systems, not all pesticides remain on a plant’s exterior. Systemic pesticides are chemicals that are actually absorbed by a plant when applied to seeds, soil, or leaves. The chemicals then circulate through the plant’s tissues, killing the insects that feed on them. Use of these pesticides on food crops began in 1998, and has steadily increased during the past 10 years. Unlike with traditional insecticides, you can’t wash or peel off systemic pesticide residues.

The four main systemics used on food crops (listed below) are members of the nitroguanidine/neonicotinoid group of chemicals, which has been implicated in the mysterious colony collapse disorder that has killed millions of bees. (See our article Colony Collapse: Are Potent Pesticides Killing Honeybees?)

Imidacloprid can be applied to many vegetables (including tomatoes and leafy greens) right up to the day they’re harvested.

Thiamethoxam was first approved as a seed treatment for corn in 2002, and thiamethoxam products that are applied to the soil have since been approved for use on most vegetable and fruit crops. 

Clothianidin is used as a seed treatment on canola, cereals, corn and sugar beets, and as a soil treatment for potatoes.

Dinotefuran can be applied to soil or sprayed on leafy greens, potatoes, and cucumber family crops.

When the Pesticide Action Network reviewed the results of pesticide residue tests conducted by the U.S. Department of Agriculture from 1999 to 2007, numerous samples contained residues of these systemic pesticides. For example, 74 percent of conventionally grown fresh lettuce and 70 percent of broccoli samples showed imidacloprid residues. Clothianidin was found in potatoes, thiamethoxam showed up in strawberries and sweet peppers, and some collard green samples were laced with dinotefuran.

The U.S. Environmental Protection Agency (EPA) has launched a comprehensive review of the environmental safety of imidacloprid, but we won’t have results until 2014! In the meantime, the state of California initiated its own reevaluation (currently ongoing) of all four systemics in February 2009. Among its reasons, California’s Department of Pesticide Regulation cited reports of eucalyptus nectar and pollen with imidacloprid levels up to 550 parts per billion — nearly three times the 185 parts per billion needed to kill honeybees. And deadly levels of these systemic poisons are even showing up in leaf guttation drops (water droplets that plants sometimes exude). According to a 2009 report in the Journal of Economic Entomology, “When bees consume guttation drops, collected from plants grown from neonicotinoid-coated seeds, they encounter death within a few minutes.”

Equally disturbing, it appears that nitroguanidine pesticides can persist in soil for 500 days or more, which creates a high risk scenario. After one or two applications, plants grown in treated soil may produce toxic pollen, nectar, and guttation droplets for more than two seasons. All the while, the entire treated area will be moderately toxic to beneficial earthworms, carabid beetles, lady beetles, predatory pirate bugs and more.

There is no scientific evidence yet that says food laced with neonicotinoids will harm humans, but why is the EPA allowing systemic pesticides on food plants in the first place? Do people really want to eat pumpkins that are so full of poison that they kill every cucumber beetle that dares take a bite? Looking beyond food plants, does the use of systemic pesticides to grow perfect roses justify the deaths of millions of bees and other insects? We need to set things right and learn (once again) this important lesson: When we let a novel, man-made chemical loose in the food chain, we can’t be entirely certain of what will happen next. This new contamination of our food is yet another reason to grow and buy organic.

Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on .

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