Drought & Grasshoppers Assail Area Pecan Trees

Agricultural Division
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Drought & Grasshoppers Assail Area Pecan Trees
Summer, 1998

Local lawns, gardens, pastures, and flowerbeds aren't the only things under attack this summer from drought stress and ravenous grasshoppers — trees and shrubs also are taking a beating.

Close-up photo of a grasshopper devouring a bull nettle leaf after other green plantlife has been eaten by the horde of invaders in Southern Oklahoma.

On especially young trees and shrubs, the effect could be fatal, according to Scott Landgraf, soil and pecan specialist at The Noble Foundation in Ardmore. Landgraf said he has been asked about tree damage from grasshoppers stripping off the leaves, a problem faced by many deciduous trees, including fruit and nut-bearing trees like the profuse pecan trees in the area.

As grasshoppers run out of tender plants on the ground, they're taking to the air — and onto trees.

"Defoliation of a tree during the growing season is never good," Landgraf said. "It is usually not immediate death, but it could be life threatening if the tree initiates new growth later into the fall."

Landgraf said new growth is usually in response to rainfall — something the area is as short on as it is long on grasshoppers. If new growth on trees and shrubs doesn't have time to harden before the first frost, freeze injury is inevitable, he said.

The severity of freeze injury depends on how succulent the new growth is when it freezes, and the severity of the first and subsequent freezes. Landgraf said a severe winter, after defoliation followed by some regrowth, could result in "extreme die back and maybe even death."

Pecan leaves decimated by devouring grasshoppers at the Noble Foundation's Red River Demonstration and Research Farm in Love County, Okla.

"I would encourage people who have the capability to water their trees now to stimulate new growth that will have time to harden off before fall freeze," Landgraf said. "As new growth develops, a labeled insecticide such as Sevin (dust or spray) should be applied to the leaves for protection against grasshoppers."

He added that nuts will not form on defoliated trees.

The ongoing drought also is critical for this year's pecan harvest.

"The water demands of pecan trees are at their highest in August and September," he said. "We expect to see a tremendous drop in the pecan harvest in August if we don't see rainfall by then."

He said watering individual trees might also help alleviate future defoliation this summer, since grasshoppers seem especially prone to select stressed trees, such as those growing in thin soils or those especially affected by drought conditions. Landgraf advises against mass spraying of trees, however, such as on commercial pecan operations.

"The concern with pecan trees is that spraying trees with any of the insecticides labeled for grasshoppers will reduce beneficial insect populations as well," Landgraf said. "The killing of those beneficial insects could release aphids that may be an even worse problem.

"One possibility is to treat the area under the trees or vegetation in the area to which grasshoppers are attracted," he added.