Based on several years of study, ARS scientists at the agency's Southeastern Fruit and Tree Nut Research Laboratory in Byron, Ga., are offering pecan producers several suggestions to combat pecan vivipary. In addition to controlling soil moisture levels, other useful actions could include using an aphid pesticide and thinning tree nuts to prevent the disorder.
For growers trying to control vivipary, the scientists report, it's important to insure that soil moisture levels are near field capacity during the kernel-filling stage (usually September and October for most U.S. cultivars and locations). Growers also can take advantage of the early-ripening effect of a commonly used aphid pesticide. And, along with thinning excess fruit, they can harvest early to help avoid vivipary.
The scientists found that premature germination is closely associated with high temperatures during the latter stages of kernel filling, but that high temperatures alone do not necessarily lead to vivipary. It may be that a combination of high and low temperatures, such as hot days and cold nights, helps cause the disorder.
Vivipary also seems driven, at least partially, by an interaction between nut temperature--the magnitude of that temperature change during a 24-hour period — and nut moisture content. A genetic component may also contribute to vivipary.
Nuts exhibiting premature germination quickly undergo a loss in quality and become worthless, making vivipary disorder a major economic problem. While many growers may never have seen the malady in their particular farming operation, other growers in the U.S. pecan belt commonly suffer substantial marketable yield losses, which can exceed 50 percent. Its impact is usually greatest in the lower San Joaquin Valley of California, lower elevations in Arizona, and portions of the mid- to lower Rio Grande Valley of Texas.
The Southeastern Fruit and Tree Nut Research Laboratory continues to look for additional strategies and tools that growers can use to eliminate vivipary.
ARS is the U.S. Department of Agriculture's chief scientific research agency.