Why Is the Fruit Development Period Important
The most important activity in an IPM program during the fruit development period is monitoring to be sure that the controls applied during the dormant and bloom seasons were effective. Pests that are especially important during the fruit development period are aphids, mites, and rust. Rust and mites arent present every year, so it is important to monitor for them to detect a problem as soon as it appears. Catching a pest problem early increases the possibility that it can be controlled with "soft" insecticides such as oil (aphids, mites), thus avoiding the conventional insecticides (organophosphates, pyrethroids) that destroy beneficial insects and mites.
Prune fruit go through 3 developmental stages. The first begins after fertilization and is a period of rapid growth that lasts about 30 days. By the end of this stage, nearly all the cells of the fruit have been formed and the pit begins to harden. Pit hardening marks the beginning of the second stage, during which fruit size increases more slowly. The final stage is a period of rapid growth of the skin (exocarp) and flesh (mesocarp) that usually begins 4 to 6 weeks before harvest.
Fruit and flower drop may occur at any time during the season in response to environmental or physiological conditions. A large number of flowers and fruitlets may drop shortly after bloom because their ovules were not fertilized. Sometimes a drop of young fruit, often called "June drop," occurs in April or May. This is a normal process that is probably the result of competition between fruit for nutrients. In prunes, petal fall occurs around April 1 and by May 1 the fruit is about 1 inch in diameter.