Using ReTain to set fruit
ReTain can help set apples, sweet cherries and pears when applied in or near the bloom stage. It maintains longer flower receptiveness during bloom for apples and sweet cherries, and reduces ethylene production after bloom during fruit set on pears.
The process of anthesis (bloom) produces high levels of ethylene in the flower of some fruit types and varieties. Most apple varieties and sweet cherry produce high levels of ethylene during bloom. Pears produce spikes in ethylene 10 to 14 days after bloom. Ethylene ages the flowers and can cause fruit drop during the fruit set window. Controlling the ethylene can increase fruit set.
ReTain (AVG) is an ethylene inhibitor in fruit trees. Applying ReTain at the right time will reduce ethylene levels in the flower and tree, thus delaying the aging of the flowers, allowing flowers to be receptive to pollination and fertilization for a longer period. Also, after bloom in pears, the lowering of ethylene levels reduces the thinning effect of the ethylene. In other words, reducing the ethylene levels promotes greater fruit set.
Some apple varieties will benefit from applications of ReTain at king bloom and again at full bloom (three days later). Golden Supreme is a shy bearing apple variety that is very responsive to ReTain, but all varieties are somewhat responsive. Of course, most years on most apple varieties additional fruit set is not desired. But there could be certain times when it could be desired, such as frost damaged flowers, low frosty areas of blocks, shy bearing varieties, in the bottom half of trees, perhaps cider varieties where size and return bloom is not a concern.
Some sweet cherry varieties are very receptive to ReTain applications. Regina and others respond nicely to 1 pouch applied at popcorn stage with a 30% increase in set but when another pouch is applied at three days later at full bloom, an even greater set occurs as much as 40 to 80% increase in set compared to the UTC. Some shy bearing pears respond likewise but the ReTain has to be applied after bloom (10 days after full bloom).
The more ReTain applied (up to 2 pouches per acre), the greater the response. Current recommendation for sweet cherry is to apply 1 pouch per acre at the popcorn stage and another pouch two to three days later during full bloom. On apple, apply 1 pouch per acre at late pink to early bloom and again two to three days later during full bloom to special varieties and locations. On shy bearing pears, apply 1 pouch eight days after full bloom and again at 12 days after full bloom.
ReTain will help with fruit set but has to be put on early in bloom for sweet cherries and apples and after bloom on pears. The greater the dosage of ReTain, the greater the final set, but on apples this can greatly overset cropload and a disastrous heavy, heavy crop can result with no return bloom. Use this Retain tool with care.