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Pecan Paradise: OSU Ag Research furthers the land-grant mission

Monday, September 18, 2023

Media Contact: Harrison Hill | Senior Research Communications Specialist | 405-744-5827 |

Wheat and livestock often get the spotlight in Oklahoma, but the state also boasts a thriving pecan industry.

The pecan is the main fruit tree crop in Oklahoma, and the state ranks among the top five pecan producers in the U.S. In 2022, Oklahoma pecan production totaled 7.5 million pounds, adding $10.5 million to the economy. Pecans can be classified into two types: improved cultivars and native pecans. More than 80% of pecans grown in Oklahoma are native.

Pecan production in Oklahoma varies annually and regionally based on weather conditions and is highly susceptible to large-scale damage. That’s why it is important to research alternative ways to improve the health and well-being of this important economic industry.

“We work on both improved cultivars and native pecans,” said Dr. Lu Zhang, an Oklahoma State University horticulturist who specializes in pecan research.

Zhang and her colleagues are currently researching how to make pecan trees less susceptible to ice storms and spring freezes as well as how mycorrhizal fungi can increase nitrogen and nutrients in the trees. Zhang’s research agenda involves projects aimed at improving Oklahoma’s native pecan production.

Mitigating Ice Damage

Following a severe ice storm in October 2020, OSU horticulturalists began two research projects to study how managing a tree canopy might help with recovery after a pecan tree is damaged during the event.

The longest recovery periods for damaged pecan trees are caused by ice storms. Ice damage is typically more severe in pecan orchards than in other orchard crops because a pecan tree’s height, long limbs and large leaf areas are more susceptible to breaking.

“Pecan trees usually take anywhere from three to 10 years to recover sufficient productivity following severe canopy damage caused by ice storms, tornadoes or thunderstorms,” Zhang said. “Research-based information on canopy management after severe canopy loss is lacking, and producers do not have a strong understanding of when a tree can return to productivity.”

Nitrogen and zinc fertilization and irrigation are major factors that affect production recovery. In these projects Zhang and her colleagues, Dr. Niels Maness and Dr. Ali Mirchi, studied how long trees took to return to bloom at different levels of canopy loss and the role carbohydrate levels played in the process. They also studied nitrogen, zinc and irrigation management, and methods of removing epicormic shoots, which are dormant shoots beneath the bark of a tree that sprout when damage occurs.

Based on this research, they developed protocols for pruning epicormic shoots, nitrogen and zinc fertilizer application, and irrigation adjustment to accelerate a tree’s healing.

Battling Spring Freezes

Spring freeze is one of the most severe threats to Oklahoma pecan production. In 2018, late April freezes damaged up to 70% of pecan growers’ crops.

“Pecan flowers’ temperature threshold and how long they are tolerant to freezing temperatures is unknown,” Zhang said. “With some pecan cultivars, secondary buds will develop into healthy flowers if the primary buds are impaired, which functions as a fail-safe to guarantee yield. But other cultivars failed to produce or set abnormal flowers from secondary buds.”

Zhang and her colleagues evaluated and measured the critical freezing temperature and durations, flower qualities, carbohydrates and hormone levels, conducting the following research:

  • Evaluated the development and qualities of flowers exposed to different freeze temperatures for different periods of time.
  • Investigated how a primary bloom breaking and a secondary bloom flowering impacts carbohydrate and hormone levels.
  • Assessed the influence of rootstocks on flower development related to carbohydrate status and hormone balance.

The research data will be used as an index for proper practices in managing damage.

Fungi Byproducts

More than 90% of terrestrial plants can form a mutually beneficial relationship with mycorrhizal fungi in which the fungi can obtain carbohydrates from host plants. In return, fungi help the host plants absorb nutrients and water from the soil.

“Pecan truffle is a type of mycorrhizal fungi, and our current research shows that the truffle genus Tuber is naturally abundant in many pecan orchards in Oklahoma,” Zhang said.

Nitrogen is the most limited nutrient in pecan yields, and previous research shows that mycorrhizal fungi play an essential role in enhancing plant nitrogen uptake. In a new research project, Zhang and colleague Dr. Tingying Xu, assistant professor of geochemistry, will focus on increasing the efficiency of nitrogen uptake in pecan trees by surveying and selecting mycorrhizal fungi native to various pecan orchards in Oklahoma.

Zhang said her research team has successfully inoculated the fungi into 3-month-old pecan seedlings in a lab, and results indicate that pecan seedlings with fungus grow taller than those in the control group after six months of incubation.

“We will isolate mycorrhizal fungi from the pecan root, then screen and identify fungi that provide the most suitable fungal candidates to improve pecan nitrogen uptake,” Zhang said. “Then, the selected fungi will be grown and introduced into pecan seedlings. Our work will demonstrate how to introduce the best biotypes of mycorrhizal fungi into pecan orchards.”

Zhang also hopes to apply her findings to mature pecan trees in improved pecan orchards and native pecan groves as a sustainable practice for Oklahoma pecan producers.

“The pecan research conducted by Dr. Zhang and her colleagues is a demonstration of the importance of the land-grant mission,” said Dr. Scott Senseman, associate vice president of OSU Ag Research. “Pecans are vitally important to our economy and food sustainability, but like many other agricultural crops, this fruit tree faces many environmental hardships. By providing solutions to these problems, Dr. Zhang’s research teams are improving the sustainability of our pecan industry and, ultimately, the lives of Oklahomans, the nation and the world.”

Photo By: Mitchell Alcala

Story By: Alisa Boswell-Gore | Research Matters Magazine

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