Thinning and Return Bloom
Chapter authors - Teryl Roper, Brent Black
While the precise mode of action of PGR thinning agents is not clearly understood, evidence is accumulating that the carbohydrate status of the tree plays a key role in plant sensitivity. Carbohydrate status is affected by light levels (more light = more photosynthesis = improved carbohydrate levels) and by overall tree health.
This effect occurs both at the whole-tree and the individual-branch level. Overcast conditions and internal shading both make the fruit more sensitive to PGR thinning applications. Likewise, well-exposed branches under full sunlight conditions tend to be more difficult to thin.