Trunk Injection of Fruit Thinners to Regulate Fruit Set and Return Bloom in Apples

Various strategies and methods have been used to achieve and appropriate crop load on a tree to assure high quality fruit are harvested and sufficient return bloom is achieved for a commercial crop the following year.  Normally thinners are applied as a foliar spray and delivered with an airblast sprayer or similar sprayer.  Problems associated with this method of application include unfavorable weather at the time of spray application, spray drift, restricted reentry time following applications, and the potential for chemical trespass on residences in close proximity to the spray application.  We have evaluated abscisic acid (ABA), aminoacyclopropane-1-carboxylic acid (ACC) and Metamitron, all of which have abscission-promoting properties.  Our goal was to see if we could successfully apply these thinners via trunk injection and achieve similar or comparable fruit abscission when comparable doses of these were applied by traditional sprayer-applied foliar application.  Trunk injections were made to either mature Empire/M26 or Delicious/M.26 during the normal thinning time when fruit were of the appropriate size to thin.  Thinning was successfully achieve by trunk injection f ABA and metamitron and a marginal amount of thing was done with ACC.  Fruit size at harvest was a reflection of the amount of thinning that was achieved but no thinner influence fruit quality at harvest.  There was some phytotoxicity associated with the trunk injections that was associated with uneven distribution of the thinners in the trees.  Gibberellins GA₃ GA ₄₊₇ were also applied on Delicious/M.26 apple trees in July. There were no visible effects of the GA treatments.  Return bloom on trees that were injected with GAs will be discussed and compared with similar applications made as a foliar spray.