Runoff pollution from pesticides may be a major issue in the agricultural industry the world over, but a team of U.S. researchers has now developed an innovative way of making more of the spray stick to the plants.

Scientists from the Massachusetts Institute of Technology (MIT) used a clever combination of two oppositely-charged additives to the sprays that drastically cut down on the amount of liquid that bounces off.

The left half of the leaf is sprayed conventionally and retains a small amount of liquid, while on the right much more liquid remains using the new approach.

The findings were published in the journal Nature Communications, by associate professor of mechanical engineering Kripa Varanasi, graduate student Maher Damak, research scientist Seyed Reza Mahmoudi, and former postdoc Md Nasim Hyder.

Speaking to www.frehsfruitportal.com, Varanasi and Damak explained that previous attempts to reduce the droplet bounce rate had relied on additives like surfactants that reduce the surface tension.

However, tests have shown this method provides little improvement, and actually results in smaller droplets being sprayed which means they are more easily blown away.

Varanasi and his team also discovered another problem with previous attempts was that the droplet bouncing happens so quickly - in a matter of milliseconds - that most countermeasures simply didn't have time to make much difference.

The recently developed approach uses two substances, one which gives the solution a negative charge, and another that gives it a positive charge.

When the two droplets meet on a leaf surface, they form a water-attracting 'defect' that sticks to the surface and increases the retention of further droplets.

"Our inspiration was something that’s done in a completely different field called layer-by-layer deposition, which is a technique they use to deposit proteins where they spray these oppositely charged polyelectrolytes and then they act together," Damak said.

"So we thought of using that charge interaction in a completely different situation, which is simultaneous spraying and these droplets impacting on each other on the surface of the leaf.

"We realized that those charge interactions can act much faster than the usual chemical additives that people use and from there we developed this technique."

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.

In addition the polymer additives themselves are natural and biodegradable, so will not contribute to the runoff pollution.

An Indian farmer with a typical handheld sprayer, a common means of spraying in developing countries

Varanasi also explained that the new approach would not require major changes to existing equipment used by farmers - the pesticide would just need to be separated into two streams to which small amounts of each substance would be added.

The additives themselves are extracted from common, low-cost materials that could be produced locally.

"The farmers would just need to have two containers, which is not uncommon, to which they add these substances to the pesticide solution," Varanasi said.

"The farmer would do everything else as usual. It wouldn’t be a major change to their equipment."

Along with the environmental benefits, the researchers also explained farmers could make huge cost savings with the method.

"In India, for example, pesticides represent about 30-35% of the production costs of cotton, and cotton has hydrophobic leaves so runoff is a problem," Damak said.

"So if we can reduce pesticide using by 10, or even five times, it can be game changing for many farmers."

Varanasi also highlighted that the method of using solutions with opposite charges was not limited to pesticides, but could be used for any liquids that are sprayed.

"For example, in Florida farmers spray water on the crops to protect against frost damage, and this method could reduce the amount of water used," he said.

The team is now hoping to carry out greenhouse and field trials, and then move on to commercialization.

"We've received a bunch of enquiries from farmers so we're excited to start working with them," Varanasi said.

"We want to do some control studies to quantify the benefits, which will hopefully be in the next year or two. We are already setting up a small greenhouse facility where we can test it out in a multiple plants, and then move to a bigger farm scale."

He added he was really looking forward to working with the agricultural community and providing a positive influence.

"We have to work with the supply chain and we need to have the right business model," he said.

"Once proven at farm scale, and once we have that data point, then it becomes very convincing to funders and that can pave the way to commercialization quickly."

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