By Brad Haire
University of Georgia
“The greatest challenge to consistent pecan production is the tree’s tendency to bear a large crop for one or maybe two years followed by a small crop for a year or two,” said Lenny Wells, a horticulturist with the UGA College of Agricultural and Environmental Sciences.
This on-off cycle, or what is called alternate bearing, is something Georgia growers have dealt with since the nut was commercially introduced in the state in the 1920s. During “on” years, the tree produces a lot of nuts, but their quality can be poor. During “off” years, nut quality can be good but economic returns low because total production is low, he said.
Scientists have debated for years why the tree has this cycle, Wells said. But at its most basic level, alternate bearing is controlled by plant hormones. And hormone levels depend on the size of the previous year’s crop, or nut load.
So, the key to consistent year-to-year production is crop-load management, he said, or simply reducing the number of nuts on a tree during an on year.
Pecan harvest in Georgia starts in late October. To gather nuts, growers typically use a machine that vibrates the tree trunk, shaking the nuts from its canopy to the ground below, where they are later scooped up. The same technique can be used earlier in the season to remove some of the immature nuts, thinning the crop load during an on year, Wells said.
“When nut thinning is done correctly, it is a sound and highly effective management tool for minimizing the alternate-bearing tendency and increasing the profitability of some cultivars,” he said.
Wells conducted a two-year study using Cape Fear, a common pecan variety. Five trees were mechanically thinned in 2007, which was an on production year, and five trees were not thinned. The two-year production value of the thinned trees was $513.55 each compared to $237.94 each for the non-thinned trees.
“Not all cultivars or trees within a cultivar will require thinning in a given year, nor do all cultivars respond to thinning in the same manner,” he said. “Some cultivars may be more easily damaged than others when trunk shaking in the summer.”
The thinning technique is simple in theory, but takes skill and timely efforts, he said.
The time to thin nuts will vary with cultivar and location, as well as from year to year. But for most varieties grown in Georgia, the time will be July through early August.
If the crop is thinned too early, the nuts are small and will require forceful shaking that can damage the tree. If thinning occurs too late, the benefit for next year’s crops can be lost.
A nut’s maturity is determined by slicing through it to expose the ovule, which eventually becomes the kernel and nut.
“This thinning may not work for all growers, but it is a tool that can increase returns for growers over the lifetime of trees,” Wells said.