Technical Abstract: A field study was conducted to evaluate the effects of hydrogen cyanamide (H2CN2) on flower and leaf buds, foliage, and fruit of 'Climax' rabbiteye blueberry (Vaccinium ashei, Reade), a cultivar exhibiting erratic spring foliation following mild winters. Stems of 'Climax' in several stages of flower bud development were sprayed with H2CN2(0, 1.0, 1.5 and 2.0% v/v), and effects on leaf development, injury to flower buds, and fruit development were studied. H2CN2 increased rate of vegetative bud opening, terminal leaf area, and overall leaf canopy. Flower bud injury was excessive when H2CN2 was applied at rates > 1.5% v/v or when flower buds were at stages 4-5 of development; 1.5% H2CN2 significantly reduced yield and rendered berries more susceptible to late spring frost injury. H2CN2 dramatically increased total number of vegetative buds developed for the next season's foliage, delaying bud break in the Spring of 2001. Results of this study agreed with similar controlled environment studies in that when H2CN2 was applied at rates not exceeding 1.0% v/v and before a majority of flower buds exceed development stage 2, vegetative bud development was enhanced and damage to flower buds was minimal.