Discovery helps pesticides “stick” more; reduce runoff

A new study completed by researchers at MIT have found a new way to make pesticides “more sticky” helping them latch onto crops more effectually and potentially limiting the amount that are wasted by bouncing off plants and contributing to runoff that flows to streams and rivers.

A recent article explains that many plant leaves are hydrophobic, meaning they repel water on their leaves and absorb water mostly through their roots.

If leaves are too wet, they can become moldy and unhealthy, but this also makes it hard to get pesticides, many of which have a high proportion of water, to stay where they’re supposed to be—right on the leaves.

In fact, the study estimates that only about 2% of pesticide sprays actually stick to the plants, meaning farmers have to spray many more times the amount of pesticides that they need.

By using a clever combination of two inexpensive additives to the spray, however, the researchers found they can drastically cut down on the amount of liquid that bounces off. In the study, the pesticide spray used was divided into two portions, each receiving a different polymer substance. One of the portions was given a polymer that lent a negative electric charge, while the other was given a polymer that lent a positive charge. When they mix them together, they formed a hydrophilic surface on the plant itself, meaning that future drops of liquid are more likely to stick.

“All [this] happens during the time [the spray] is spreading and before the droplets starts a retraction that leads to their bouncing away, researcher Kripa Varanasi said in the article.

Based on the laboratory tests, the team estimates that the new system could allow farmers to get the same effects by using only 1/10 as much of the pesticide or other spray. And the polymer additives themselves are natural and biodegradable, so will not contribute to the runoff pollution.

"We can use normal sprayers, with two tanks at a time, and add one material to one tank and the oppositely-charged material to the other," Maher Damak, another researcher involved in the study, said. The farmer "would do everything as usual, just adding our solutions."

The researchers are also experimenting with different sprayer designs that could simplify the process further and potentially eliminate the need for two separate tanks.

The next step, Damak explains, is to take the results that have been demonstrated in the laboratory and develop them into a practical system that can easily be implemented in the field and carry out real-world tests during the coming year.

The project was developed in collaboration with the MIT Tata Center for Technology and Design, which aims to develop technologies that can benefit communities in India as well as throughout the developing world. Spraying of pesticides there is typically done manually with tanks carried on farmers' backs, and since the cost of pesticides can be a significant part of a farmer's budget, reducing the amount that's wasted could improve the overall economics of the small-farming business, while also reducing soil and water pollution.

Damak said he has already has traveled through India to see exactly how small farmers there are carrying out their spraying currently and how the team’s findings can assist. "That helped me see what the conditions are on the farms, and what they use for their spraying applications," he said.

In addition to pesticide spraying, the researchers explained the same approach could be useful in other applications, such as the spraying of water onto plants to prevent frost damage in places like Florida, where citrus crops can be severely damaged by frost but water supplies are already constrained.

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