Researchers have used nanotechnology to kill weeds using sharply reduced amounts of a common herbicide, according to papers published in multiple journals.

Researchers with the State University of Londrina and the State University Paulista Julio de Mequita Filo in Brazil used atrazine contained inside microscopic capsules made of Poly(ϵ-caprolactone) (PCL), a type of polymer, against slender amaranth and hairy beggarticks weeds.

Researchers gathered samples of hairy beggarticks from the wild, and purchased slender amaranth seeds from Bayer, then grew them in prepared soils in a greenhouse. They treated the weeds about 30 days in with distilled water, empty nanocapsules, regular atrazine, and nanocapsules containing atrazine. They also tested a separate group of plants with atrazine at 1/10th the commercially recommended level and another with atrazine in nanocapsules at a similar level.

All plants were then checked for the level of photosynthetic activity, and harvested and evaluated for relative growth rates.

In the beggarticks plants, the results showed that treatment with the encapsulated atrazine showed negative relative growth rates for both roots and shoots. The diluted mixture of encapsulated atrazine resulted in lower relative growth rates for both roots and shoots than either the diluted atrazine mixture or the recommended level.

The encapsulated atrazine also reduced relative growth rates for both roots and shoots in slender amaranth (with a negative shoot rate) more effectively than the diluted or recommended atrazine.

The unloaded capsules and water treatments had no effects, according to the paper.

"Given that unloaded PCL nanocapsules led only to minor effects on the analyzed parameters, the increase of the herbicidal activity cannot be explained by a phytotoxic effect of nanocapsule components per se," the authors wrote. "Confersely, it may be associated with the modified release of atrazine by the nanocapsules, with a better adhesion of the nanoformulation to the leaves or with the uptake of the nanocapsules by the leaf stomates, thereby preventing atrazine loss into the environment and improving the deliver of the herbicide to the target organism."

In other words, the capsules delivered the herbicide more precisely, allowing far smaller amounts to be used.

The development is significant because other members of the amaranth genus — Palmer and giant amaranths and waterhemp — can ruin corn and soybean crops.

Atrazine — used commonly when other, more common forms of pesticide don't eliminate resistant weeds — is under review by the U.S. Environmental Protection Agency. The EPA is considering regulations that would allow growers to use much less atrazine to combat weeds.

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