Technical Abstract: Insufficient fruit-set can limit profitability of specific pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars. The present study examined efficacy of ReTain® (Valent BioSciences, Libertyville, IL), a natural ethylene inhibitor, for increasing fruit-set in pecan trees grown at three distinct locations within the U.S. pecan-belt. Up to four years of field studies found that timely post-pollination ReTain® sprays [132 mg•L-1 a.i. (11.7 oz./acre)] to canopies could increase fruit-set of ‘Desirable’, and, accordingly, increase crop yield by 16-38% in trees carrying a “moderate to heavy” crop; nevertheless, was ineffective for increasing fruit-set on trees carrying a “light” crop-load. The ReTain®-associated increase in yield did not necessarily decrease yield the following crop year. Proper usage of ReTain® appears to offer commercial producers of ‘Desirable’ nutmeats a practical tool for managing crop-load via regulation of Stage-II drop (i.e., June-drop).