Pecans trees are water loving. In 1578 when Spanish explorer Cebeza de Vacas shipwrecked on Galveston Island the local Native Americans befriended him. De Vacas noted that the Native Americans would visit a “River of Nuts”. They would enter downstream consuming the nuts as they moved upstream.
Pecans naturally occur along shores of rivers and flood plains, tracking the Mississippi River and its tributaries from Illinois down into the South. The large nuts of pecan trees are transported down these waterways to new locations. The trees can even withstand long periods of flooding, a unique trait within hickories. Every single part of pecan’s annual growth cycle–flower formation, development of fruit from flower, nut elongation, kernel development, to name a few–requires optimum levels of rainfall. Last year’s rainfall determines total nut production. This year’s determines nut quality. To initiate and continue nut growth an average of one to two inches of rain per week are required during the growing season between April and October. This works out to 55 inches a year. The only region in the U.S. to hit this level of rainfall, with an obligingly long growing season, is the South.
However, too much rain can decimate any given year’s total pecan production.
“The rain we’ve had in the last 30 days is the worst case scenario for growing pecans…it’s just too much,” Elbie notes during my visit back in July of 2013. Most parts of North Carolina at that point in the year reached over 150-300% of their normal rainfall. At that point in the season, North Carolina was already 10 inches of rainfall above normal. What Elbie could not have known at the time was that even more rainfall was on the way. By the end of the season, 80% of North Carolina’s pecan crop was lost to scab.
“You ever notice one of those pecans that you break open, and it ain’t nothing but black and empty on the inside?” Elbie questions me. I do indeed know. There is nothing more heartbreaking than finding black dust inside a pecan shell when you are expecting a golden nut. What Elbie is referring to is pecan scab, Fusicladium effusum, a fungus that attacks both leaves and nuts of pecan trees. And as most funguses do, pecan scab prefers lots of moisture. Rainfall sparks pecan scab. The leaves and nuts need to be moist for 8-12 hours for fungal spores to penetrate leaves and nuts. Once fungal growth commences black lesions form on the pecan leaves and nut shuck. On leaves, pecan scab can result in defoliation and death of the vulnerable shoots. On the nut shuck, pecan scab can slow or prevent normal nut growth reducing pecan yields. Pecan scab is a voracious plant predator. Some pecan groves can require nearly a dozen fungicide sprayings before scab will be eradicated. In Florida, in a normal rainfall, pecan scab can result in 50-100% loss of pecan nuts if certain pecan tree varietals go untreated. In wet years this increases to 100%.
The irony of a tree that prefers flood plains being so susceptible to a disease that thrives in moist conditions is yet another paradox underlying pecan pies.