The popular herbicide paraquat works well and is inexpensive, but emerging research shows a correlation of paraquat exposure and Parkinson's disease, reported Kerry Klein on Valley Public Radio.

Klein met with UC Cooperative Extension weed advisor Kurt Hembree at an almond orchard near Selma that was clear of weeds. Growers kill weeds because weeds kill crops, Hembree said.

"Direct competition for water and nutrients. Whatever the tree likes, the weeds like," he said.

Hembree explained how the paraquat works.

"Paraquat's a contact-type herbicide," he said. "In other words, it's a material that, if you sprayed it on a plant, it'll disrupt the plant's cells. And basically in five or six days, whatever it touches, it spots up and it causes necrosis and death on the tissue."

Paraquat is toxic, so it requires careful handling to protect the safety of applicators.  

“Something like paraquat, you're going to wear rubber boots, you're going to wear goggles while you're spraying,” Hembree said. “You don't want to get this stuff on your skin or on your mouth or anywhere.”

The KVPR story said paraquat is among the top 10 most common herbicides in California, and the San Joaquin Valley gets more than three-quarters of the state total. Caroline Tanner, a neurologist at UC San Francisco, was also interviewed for the story.

“People who mixed or applied this chemical had more than double the risk of developing Parkinson's disease compared to people really very similar as far as where they lived, even what they did for a living, age and gender,” she said.

However, people who were careful with personal protective equipment didn't have a greater risk of Parkinson's disease, Tanner said.

Weeds will compete with a new orchard for water, sun and nutrients, and interfere with harvest in mature orchards. Weeds in this orchard were killed with an herbicide.