Methionine-Riboflavin and Potassium Bicarbonate-Polymer Sprays Control Apple Flyspeck and Sooty Blotch

Flyspeck (FS) and sooty blotch (SB) are widely distributed and potentially economically damaging fungal diseases of apple and pear. They are particularly significant in warm and moist climates, on late-maturing cultivars, in dense tree canopies, or where growers apply no or few fungicides. To provide an alternative to conventional fungicides for orchards, we tested spray programs based on either a methionine-riboflavin (MR) formulation or potassium bicarbonate-oil polymer for FS/SB control on three scab-resistant apple cultivars -- Prima, Jonafree, and Freedom -- in two Wisconsin orchards between 1998 and 2000. Both programs lowered FS/SB. MR reduced disease significantly and as well as or better than sulfur in every year and on every cultivar. Potassium bicarbonate plus oil, though effective, did not perform as consistently as MR. Both treatments warrant further study to ascertain their efficacy under various regimens, to clarify their modes of action, and to determine their usefulness to growers who wish to avoid or minimize reliance on conventional fungicides. Accepted for publication 18 June 2001. Published 6 July 2001.