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Why Is the Bloom Season Important to an IPM Program?

Bloom season, which extends from the green tip stage to petal fall, is the best time to manage a number of prune pests. There is not a lot of foliage at this time, making good spray coverage easier to achieve than later in the season. Also, many of the key pests are present in the trees during bloom.

Timing for some actions is based on an estimate of when a certain proportion of the flower buds are fully open—for example, 5% bloom and 10% bloom are estimates of when the first 5% or 10% of flower buds have reached the full bloom stage. For purposes of pest management, the term "full bloom" refers to the point at which the majority of flowers in the orchard are fully open; by this time some will be past full bloom, while others will be at earlier stages. The proportion of flowers that are fully open when the orchard is at full bloom can vary substantially depending on winter chilling. In high chilling years, as many as 80% of the blossoms may reach full bloom at the same time. In low chilling years, the proportion may be below 50%.

Click on photos to enlarge

Bloom Stages of Prune
Prune fruiting spur with buds at the green tip stage.
Green tip
French prune at the first white stage of bloom.
First white tip
Prune blossoms at popcorn stage.
Prune blossoms at full bloom stage.
Full bloom
Prune blossoms at petal fall.
Petal fall
Prune blossoms at jacket stage.
Jacket stage
Prune at jacket split stage.
Jacket split

Choice of Insecticides
Bloom time applications of Bacillus thuringiensis (Bt) for control of peach twig borer help to keep leafroller, green fruitworms, western tussock moth, and cankerworm populations under control. Also, using Bt at bloom is easier on honey bees and other beneficials than postbloom use of other materials. The Bt spray is usually combined with the brown rot spray. When oil is added to this spray, it also controls aphids and improves the effectiveness of the fungicide used for brown rot control.

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

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