2018 Crop Protection Guide for Tree Fruits in Washington

Bioregulator Sprays

Monday, March 25, 2019

Promotion of Apple and Pear Fruit Size

When used in a chemical thinning program, BA (MaxCel, Exilis Plus, Exilis 9.5SC) may increase fruit size beyond the effect of reduced crop load; cytokinins often increase cell division, and BA-treated fruit may have higher cell numbers resulting in larger fruit size. This effect may be achieved in apples with minimal fruit thinning by using sequential applications of BA at concentrations lower than those used for standard thinning programs. To promote apple fruit size while still maximizing fruit set, apply 2-4 sprays of BA at 3-10 day intervals, starting at petal fall; please refer to product labels for appropriate concentrations for this purpose. Be warned, even at lower rates, BA may induce fruitlet abortion; growers should exercise caution when using these programs if additional thinning is not desirable.

Tree Fruit Research & Extension Center, 1100 N Western Ave, Washington State University, Wenatchee WA 98801, 509-663-8181, Contact Us