USE OF METAMITRON ALONE AND IN COMBINATION WITH 6-BENZYLADENINE FOR THINNING APPLES

Several experiments were conducted over a 3-year period to evaluate meta-mitron as a potential apple thinner. A block of 7-year-old ‘CandyCrisp’/M.9 apples trees was selected in 2010. Metamitron rates between 50 and 400 mg/L were applied at the 15 mm fruit size stage. All rates of metamitron thinned excessively but this response was attributed in large part to very warm temperatures following applica-tion. Similar trees were used in 2011 but treatments were applied later at the 20 mm fruit size stage. At the end of June drop, crop load was reduced by nearly 50% which was a level considered to be nearly ideal for these trees. Metamitron had few fruit effects at harvest that could not be attributed to thinner-induced reduction in crop load. In a block of mature ‘Pioneer McIntosh’/M.9 apple trees metamitron was applied at rates of 150 to 300 mg/L alone and in combination with 6-benzyladenine (BA) in two separate years but using different trees each year. Excessive thinning occurred when 300 mg/L metamitron was applied alone or in combination with BA. When 150 mg/L was applied less thinning occurred and the resulting crop load was reduced to a commercially acceptable level. Metamitron had minimal influence on fruit maturity parameters. It is concluded that metamitron may be a useful thinner on apples. Especially interesting is the observation that it was effective at thinning larger-sized fruit, a characteristic that is extremely rare for a mainstream apple thinner.