Charging pesticide droplets "pins them to leaf surface"

Pesticides and other sprays can be made much more effective with a new technique to prevent them bouncing off crops, according to US researchers.

Varanasi (right) with co-author, MIT graduate student Maher Damak - Image: Melanie Gonick
Varanasi (right) with co-author, MIT graduate student Maher Damak - Image: Melanie Gonick

A team from the Massachusetts Institute of Technology (MIT) found that a combination of two inexpensive additives to the spray drastically reduced the amount of liquid that bounces off, by overcoming the natural hydrophobic (water repelling) effect of many plant leaves.

One polymer is added to some of the spray solution to give it a negative electric charge, the other causes a positive charge in the remainder. When two oppositely-charged droplets meet on a leaf surface, they form a hydrophilic (water attracting) "defect" that sticks to the surface and increases the retention of further droplets.

Earlier efforts to overcome the problem used chemical additives such as surfactants, but the droplet bouncing happens too quickly for these to have much effect.

"So we thought, what else can you do? And we started playing around with charge interactions," associate professor of mechanical engineering Kripa Varanasi said.

Laboratory tests suggest the new system could allow farmers to get the same effects by using only one-tenth as much pesticide or other spray, and would require only minor changes to existing equipment, the team claims.

They are also experimenting with different sprayer designs to avoid the need for two separate tanks.

The findings were published yesterday in the journal Nature Communications.

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