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Why Is the Fruit Development Period Important in an IPM Program?

The fruit development period is vital for ensuring that the controls applied during the dormant and bloom seasons were effective. Controlling aphids and mites is especially important during the fruit development period.

Since mites aren’t present every year, 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 you can control it with "soft" insecticides such as oil (for aphids and mites) and avoid the conventional insecticides (such as organophosphates or pyrethroids) that destroy beneficial insects and mites.

Plum 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 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. Many flowers and fruitlets may drop shortly after bloom if their ovules were not fertilized. Sometimes a drop of young fruit, often called "June drop," occurs in April or May. This normal process probably results from competition among fruit for nutrients. In plums, petal fall occurs around April 1, and by May 1 the fruit is about 1 inch in diameter.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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