Texas A&M scientists solve major problems plaguing Valley citrus orchards

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Texas citrus is confronting myriad challenges these days, from pests to disease to drought, though two scientists with Texas A&M University have given the industry a fighting chance.

It goes back to 2013, when Dr. Mamoudou Setamou, professor and director of the Texas A&M Kingsville Citrus Center, and Dr. Olufemi Alabi, professor and extension specialist with the university’s AgriLife Extension Service, were going up against the Diaprepes root weevil, which was attacking trees around Bayview and other areas in the Rio Grande Valley.

In a recent interview they explained the threat from Diaprepes, a ground-dwelling insect whose larvae feed on a citrus tree’s root systems while the adults live on the foliage, where they lay their eggs. When the larvae hatch they fall to the ground and penetrate the soil, where they start feeding on the tree’s hair-like roots, destroying its ability to take in moisture and nutrients.

The larvae develop into pupae, which turn into adults, which emerge from the soil and climb up the tree to start the life cycle all over again.

“We came up with this approach of laying this black plastic mesh on the grow floor to disrupt the life cycle,” Setamou said. “By laying this ground cover, you disrupt the establishment of the larvae. They cannot bury themselves in the ground, and the adults cannot emerge because of the plastic barrier.”

They noticed that trees retrofitted with the plastic ground cover not only recovered from the weevil damage but got bigger, which gave them the idea of using the ground cloth in the planting of new trees. The scientists compared trees planted using the barrier method, which also incorporates a raised bed, with trees planted the traditional way and observed remarkable results.

“It’s day and night,” Alabi said. “Within the space of one or two years you see a dramatic difference in growth and foliage and everything. And then when we established a new orchard with this system, we found that actually those trees, they grow faster compared to the traditional planting method. And within three years they actually produce a commercial-grade crop.”

They didn’t realize it at the time, but in solving the weevil issue — a chemical-free solution no less — the barrier method proved beneficial in other ways. For instance, the ground cloth also serves as deterrent to weeds and vines, while substantially reducing the amount of water lost to evaporation.

The barrier retains so much water, in fact, that the traditional watering method — flood irrigation — began killing trees from too much water.

“This area of water conservation has been investigated further, and what we realized is that many growers who are using our system … save 30-40% of water,” Setamou said. “You can … mitigate the impact of drought by saving water. This is one major benefit of this system that we didn’t think of when we started.”

Rather than flood irrigation, the scientists recommended micro-sprinklers or pressurized drip systems for the new planting system.

Glen Martin, grove care manager for Lone Star Citrus Growers in Mission, said the barrier/drip irrigation system “is the way to go.”

“The old conventional flood irrigation is going by the wayside because of the savings in water,” he said. “It’s more efficient, it does a lot better job and we can bring trees to market with production faster.”

Martin said drip irrigation makes it possible to dial in precisely how much a tree gets in terms of water, nutrients and insecticide — a much more efficient way of doing things. Meanwhile, the water-saving aspect is invaluable in times of prolonged drought, he said.

“Flood irrigation required two acre-feet of water to irrigate one acre of citrus grove,” Martin said. “With a pressurized drip system, we only use 37% of an acre-foot now.”

Another huge benefit of the new system is that the healthier trees it produces have a better defense against citrus greening, one of the world’s most devastating citrus diseases, spread by a tiny insect called the Asian citrus psyllid.

Greening has taken a heavy toll on Florida’s citrus industry and is pervasive in the Valley as well. Also known as Huanglongbing, or HLB, the disease leads to rapid tree decline due to the loss of the fine root hairs that absorb water and nutrients, Alabi said.

“When a tree cannot get enough nutrients and water uptake, this is what leads to the collapse that is associated with greening,” he said. “But with this (barrier) method, those trees are able to regenerate new root growth.”

Setamou added that trees planted with the new system are vigorous from the start because of higher root mass.

“Even if they get infected with greening they do not collapse because their roots are more vigorous and they have the ability, as Femi said, to regenerate new fibrous root, and that allows them to continue uptaking water and nutrients,” he said. “So they do not get affected as much as the traditionally planted trees.”

Valley citrus growers have embraced the new system, with nearly 5,000 acres already planted using it, Setamou said, describing it as “the way of the future.” Growers in Florida, Mexico and even Spain and Morocco are experimenting with the system, he said, and Alabi noted its relative simplicity.

“Major impactful research does not need to be very complicated,” he said.

The research project was funded by the HLB Multi-Agency Coordination Group, an emergency response task force implemented by the Department of Agriculture, and USDA’s Plant Health Inspection Service.

Alabi’s and Setamou’s research and the impact it’s having on the Valley citrus industry is highlighted in a new video, “Citrus Growers Endorse New Texas A&M Tree Planting Method,” which can be viewed on YouTube.

Dale Murden, Valley citrus grower and president of Texas Citrus Mutual, said tree health is the most effective defense against disease and the new barrier method provides that.

“We’re saving water, we’re saving pesticide use, and we’re keeping the trees healthier,” he said. “I think that’s key until some scientist can find a cure for some of these diseases like greening.”

Nearly all new citrus planting in the Valley is using the new method, Murden said, noting that the industry was in dire need of a leg up after everything it’s endured in recent years — Hurricane Hanna in 2020, Winter Storm Uri in 2021, years of drought, and last March, flooding.

“That we’re here at all is amazing,” he said. “Whether it was an accident or not, it’s darn sure helping us move forward in some really, really tough times.

“The only thing this planting design can’t do is stop municipal growth. I’ve been down here my whole life, and I just am blown away by what we’re taking out of agriculture and planting in concrete. You’re never going to get that back. This region was built on agriculture, but it ain’t going to be here forever.”

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