Technical Abstract: Excessive fruit-drop is a major problem in many tree-fruit and tree-nut crops. A substantial percentage of fruit drop 4-6 weeks post-pollination (i.e., June Drop). This drop is especially severe for certain pecan (Carya illinoinensis) cultivars, such as 'Desirable' cv., with as much as 90% of the potential crop aborting. Field studies found aminoethoxyvinylglycine (AVG/ReTain) and forchlorfenuron (CPPU/Prestige) to substantially reduce fruit-drop by pecan trees in orchards. AVG is efficacious when applied as a foliar spray to canopies just after the conclusion of pollination at 66-132 mg a.i. per L and CPPU is efficacious at 15-30 mg a.i. per L. Gibberellin-A3 (ProGibb) at 100 mg a.i. per L reduced drop by about 14 % in heavy crop trees, whereas Gibberellin-A4+7 and 6-Benzyladenine (Promalin) at 50 mg a.i. per L was ineffective. Activity by three distinctly different classes of plant growth regulators affecting three different classes of endogenous regulators appears to indicate that either two or more mechanisms likely regulate fruit drop or that a single mechanism is subject to influence at difference points by different classes of growth regulators. AVG or CPPU increased fruit retention by ' 30% in trees supporting relatively heavy crop loads, but did not retain fruit in trees with light crops. AVG and CPPU are potentially useful for increasing crop yields in moderate to heavy crop load trees. Unfortunately, enhanced fruit retention leads to reduced flowering the following growing season via pecan's innate alternate bearing physiological characteristic.