Planting method is thwarting weevils that can ravage Texas citrus groves

An illustration of a bug tripped on plastic mesh

Image: Research Communications and Public Relations

A planting design that outwitted a weevil in Texas citrus groves has yielded numerous other benefits for growers and brought better quality oranges and grapefruits to consumers, according to experts with Texas A&M AgriLife.

In 2000, the Diaprepes root weevil was found to be chewing up Texas citrus tree roots, then busting through the soil and up the tree to feast on leaves. Researchers began looking for a way to disrupt the weevil’s path.

By 2009, studies found all it took to stop the pest was a layer of plastic mesh over the soil beneath the tree, according to lead scientist Mamoudou Sétamou, a professor in the Department of Agriculture, Agribusiness, and Environmental Science at the Texas A&M University-Kingsville Citrus Center in the Rio Grande Valley town of Weslaco.

The plastic forms a barrier that the weevil cannot penetrate either from the ground up or from the tree to the soil, researchers said, and disrupts the pest’s life cycle.

But after several years, Sétamou and others on the project realized that with field work, irrigation of the trees and washing rains, soil would become deposited on top of the plastic mesh layers. That led the team to try planting citrus trees on raised beds of soil and then covering the beds with plastic mesh. This design has proven effective in stopping Diaprepes root weevils and preventing soil accumulation to build.

And that might have been the end of the story, but the research team began to notice other benefits after years of watching for the weevils.

Olufemi Alabi, a Texas A&M AgriLife Extension Service plant pathologist in Weslaco, said the planting method also has proven to save the growers money on inputs while yielding more fruit per acre.

“Traditionally, the planting density in the Rio Grande Valley is 121 trees per acre,” said Alabi, who joined the project in 2013. “With the new planting design, growers can easily increase this to 165-218 trees.”

The raised beds are 10-feet wide at the base, slope to 8 feet at the top and are about 18 inches tall, Alabi said. The plastic mesh is applied across the beds in a continuous length from one end of the row to the other.

The configuration has saved irrigation water, Alabi said, because the plastic mesh reduces evaporation from the root zone meaning less water is needed. The method also reduces the need for chemical sprays against the weevils and weeds, which can’t grow through the plastic mesh.

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