Pecan Scab Hours Website Lets Producers Know When It’s Time to Spray
Arkansas-based research provides thresholds for trees of varying susceptibility
By John Lovett – Apr. 14, 2025
QUALITY CHECK — Jackie Lee, director of the Fruit Research Station, developed the Pecan Scab Hours website based on several years of research in Arkansas. (U of A System Division of Agriculture photo)
FAYETTEVILLE, Ark. — Arkansas pecan growers have an easy-to-use online tool to help them determine when to spray a fungicide to ward off “pecan scab,” a fungal disease that degrades pecan quality.
Jackie Lee, associate professor of horticulture and director of the Fruit Research Station for the Arkansas Agricultural Experiment Station, developed the Arkansas Pecan Scab Hours website with the Arkansas Cooperative Extension Service in 2022. Arkansas pecan producers grow between 2 and 8 million pounds of pecans annually.
The experiment station and cooperative extension service are the research and outreach arms of the University of Arkansas System Division of Agriculture.
“Growers have reported that the adviser has saved them having to spray, which saves them money and maintains the quality of their pecans,” Lee said. “We’ve also had growers say they didn’t realize how much they needed to spray to get higher quality pecans.”
The fungus Cladosporium caryigenum causes pecan scab. Optimal conditions for development of the fungus are when the temperature is consistently above 70 degrees Fahrenheit and relative humidity is above 90 percent. Every hour above those conditions is recorded as a “pecan scab hour.”
The website begins reporting “pecan scab hours” by individual county in April. However, Lee said pecan growers usually would not need to use the site until pecans start breaking bud, which is usually in April-May.
“At the site, you can type in your county, and it will show you how many pecan scab hours you have collected in the past 14 days,” Lee said. “But you can also personalize it by selecting your county and putting in your last spray date to obtain the number of pecan scab hours you have accumulated since your last spray date.”
Lee developed the site with inspiration from a study by scientists in Oklahoma State University’s entomology and plant pathology department evaluating two pecan scab prediction models. To tailor the prediction models to Arkansas, she conducted several years of research at three sites in Arkansas — Mayflower, Morrilton and Clarksville — with pecan tree varieties that had low, moderate and high susceptibility to pecan scab.
Thresholds of “pecan scab hours” are provided by the online tool based on this research in Arkansas. Fungicide applications are estimated to be effective for 10 to 14 days, depending on weather conditions, Lee said. Growers should consult Arkansas extension publication MP154, Arkansas Plant Disease Control Products Guide, for a list of approved fungicides.
Support for the research was provided by a U.S. Department of Agriculture Specialty Crop Block grant administered by the Arkansas Department of Agriculture.
According to the 2024 Arkansas Agriculture Profile, Arkansas ranks eighth in the United States for pecan production, with 9,766 acres of pecan trees reported in 2022.
Sherri Sanders, White County Extension Agent for agriculture, notes at a Cooperative Extension Service web page on pecan scab that while large-scale growers may have the specialized equipment for spraying pecan trees, homeowners with fewer trees may try practices that limit the fungal pathogen sources before hiring a commercial sprayer.
Pecan scab mitigation practices would include removing and destroying all fallen leaves, shucks and nuts each winter or in the early spring before buds begin to swell. The fallen leaves and nuts can be primary sources of new infections in the spring. Removing damaged twigs and limbs by selective pruning should also be practiced during the dormant season, Sanders added.
To learn more about the Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website. Follow us on 𝕏 at @ArkAgResearch, subscribe to the Food, Farms and Forests podcast and sign up for our monthly newsletter, the Arkansas Agricultural Research Report. To learn more about the Division of Agriculture, visit uada.edu. Follow us on 𝕏 at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit uaex.uada.edu.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on three campuses.
Pursuant to 7 CFR § 15.3, the University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services (including employment) without regard to race, color, sex, national origin, religion, age, disability, marital or veteran status, genetic information, sexual preference, pregnancy or any other legally protected status, and is an equal opportunity institution.
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