Orchard elevation influences scab damage of pecan nuts more than rainy days

Authors: SPARKS, D - University Of Georgia; BERTRAND, P - University Of Georgia; BRENNEMAN, T - University Of Georgia; Yates, Ida

Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2008
Publication Date: 3/1/2009
Citation: Sparks, D., Bertrand, P., Brenneman, T., Yates, I.E. 2009. Orchard elevation influences scab damage of pecan nuts more than rainy days. Journal of Horticultural Science and Biotechnology. 84:137-142.

Interpretive Summary: Scab is a disease caused by a fungus that attacks developing pecan leaves and fruit. This disease may decrease crop production causing growers to loose millions of dollars, especially in the southeastern USA during certain seasons. The objectives of this study were to determine the relative importance of rain and geographic elevation on occurrence of this disease. Data on nut growth suppression from scab were collected from several sites as well as weather data from the nearest National Climatic Center to the site. Statistical analyses were used to develop equations to characterize the influence of rain and elevation on scab suppression of nut growth relative to distinctive time intervals of fruit and leaf maturation. The analyses demonstrated that scab-mediated inhibition of nut growth increased as rain increased for most time intervals and provided evidence to explain the conflict between the impact of experimentally induced and naturally occurring scab during pecan fruit development. Unlike rain, increasing elevation decreased scab-mediated inhibition of nut growth and had twice the effect of rain. The results of this study demonstrate three important factors that influence the success of pecan production in the southeastern USA. One, elevation is critical in selecting sites for orchard establishment, both among and within geographic areas. Two, the duration of rainy periods during specific stages of fruit development dictates the severity of scab damage. Three, apparent spore formation from leaf-scab lesions increase scab severity on later-formed fruit.

Technical Abstract: The fungus, Fusicladosporium effusum, (G. Winters) Partridge & Morgan-Jones, causes a disease on pecan [Carya illinoinensis (Wangenh.) C. Koch] leaves and fruit in the southeastern USA. Fruit infections severely reduce nut production and could be minimized with a more comprehensive understanding of the abiotic factors impinging on disease severity. The objectives of this study were to i) investigate the impact of rain and the geographic elevation on decreasing pecan nut growth due to scab disease and ii) to determine the relative influence of the two factors. Rainfall and elevation data were obtained from the National Climatic Data Center, USA. Data on nut growth suppression from scab were collected from several sites for a period of years. Stepwise multiple regression equations were developed to characterize the influence of rain and elevation on scab suppression of nut growth relative to distinctive time intervals of fruit and leaf maturation. The analyses demonstrated that scab-mediated inhibition of nut growth increased as rain increased for most time intervals and provided evidence to explain the conflict between the impact of experimentally induced and naturally occurring scab during pecan fruit development. Unlike rain, increasing elevation decreased scab-mediated inhibition of nut growth and had twice the effect of rain. The results of this study demonstrate three important factors that influence the success of pecan production in the southeastern USA. One, elevation is critical in selecting sites for orchard establishment, both among and within geographic areas. Two, the duration of rainy periods during specific stages of fruit development dictates the severity of scab damage. Three, apparent spore formation from leaf-scab lesions increase scab severity on later-formed fruit.