The 2011 ASHS Annual Conference

The increase in organic pear acreage in the western U.S. has created the need for an alternative to the standard, very effective 1-napthaleneacetic acid (NAA), which is normally applied 7 to 10 days prior to the beginning of pear harvest. The fermentation by-product plant growth regulator ReTain^®, aminovinylglycine (AVG), inhibits ethylene production and is acceptable for organic use. Multiple trials have been conducted since the late 1990s to determine if pre-harvest applications could 1) extend the harvest window by maintaining fruit firmness, and 2) replace NAA as a “stop drop” in organic pear orchards, since ReTain has been adopted for this use with anecdotal success. Replicated single-tree and field scale, grower-applied trials were conducted on northern Califonia ‘Bartlett’ and southern Oregon ‘Bartlett’, ‘Bosc’ and ‘Comice’ trees, both organic and conventional. ReTain was applied from 1 month to 7 days prior to harvest and data collected prior to harvest through 4 months of cold storage, depending on trial. Pre-harvest data included (variously) number of fallen fruit, fruit firmness, soluble solids and fruit size. Post-harvest quality data included fruit firmness, soluble solids, CO₂ and ethylene production (also pre-harvest in one trial), color, and storage breakdown. ReTain failed to reduce fruit drop prior to commercial harvest in most of the trials, however ReTain did reduce drop of fruit remaining on trees after commercial harvest in some trials, presenting the opportunity to extend harvest. ReTain-treated fruit were firmer than NAA-treated fruit in some trials. There was generally no difference in other measured attributes. CO₂ production rate was slightly higher and fruit softer and yellower when treated 14 days prior to harvest (DPH) versus that treated 28 DPH in 2010. Pre-harvest applications of ReTain have failed to show consistently measureable benefit as a “stop drop”, however, some potential to extend the harvest window is evident. Also, one post-harvest trial showed improved storeability. Pre-harvest treatment options that should be explored include repeated treatments and varying target applications dates based on fruit maturity. In conclusion, multiple trials have as yet been unable to show the unambiguous ability of ReTain to reduce pear fruit drop and maintain fruit firmness, however positive results in some cases and the need to find alternatives for organic pear production recommend future work.