Technical Abstract: Inadequate cross-pollination of pecan [Carya illinoinensis (Wangenh.) K. Koch], a wind pollinated crop, occurred in orchard situations traditionally assumed to be generally exempt from poor pollination problems. "Off-genotypes" effectively pollinated adjacent trees when pollen from the primary pollinator was unavailable; thus the presence of such trees insures against crop losses. The beginning, ending, duration, and temporal separation of flower maturity windows changed because of tree age, or size, and due to warmer spring temperatures, therefore likely being primary factors accounting for pollination related fruit-set losses. Higher air temperatures accelerated catkin development relative to that of pistillate flowers. Flower maturity advanced in time as trees aged or grew larger. Fruit set declined sigmoidly as pollinator distance increased, with trees beyond about 48 m from the pollinators exhibiting greatly reduced fruit set. Maximum fruit-set occurred when the pollinator was only one or two rows away. Maximum fruit-set occurred when pistillate flowers received pollen within about one day after becoming receptive; whereas, no fruit set was evident when pollinated beyond four days after the initiation of receptivity. These findings indicate that orchards should be comprised of at least three appropriately positioned complementary cultivars if pollination related crop losses are to be minimized.