Why is the bloom stage important in an IPM program?

Honey bee on an almond blossom.

Bloom stage, which extends from the popcorn tip stage to petal fall, is the best time to manage a number of almond pests. Generally, bloom stage activities occur in the period between early February to late April but dates may vary according to region, variety, and weather. Some of the key pests are present in the trees during bloom. Also, since foliage is sparse at this time, good spray coverage is easier to achieve than later in the season.

Mummy removal is a critical management tool for navel orangeworm. This task must be completed before bloom. A good time to treat peach twig borer is during bloom with well-timed treatments of Bt. Bt treatments during bloom have the least negative impacts on the environment and natural enemies. Applications must be timed to larval emergence from overwintering hibernacula.

Monitoring for many other insect pests begins soon after bloom. This includes setting out navel orangeworm egg traps and pheromone traps for San Jose scale and peach twig borer.

Various pathogens, including brown rot, anthracnose, leaf blight, and scab, require treatments at different stages of bloom, so timing of fungicide treatments is often based on an estimate of when a certain proportion of the flower buds are fully open such as, pink bud, full bloom or petal fall. Therefore, familiarity with bloom stages of almond is critical in disease management.

  • For brown rot and anthracnose, treatments start at 5 to 10% bloom.
  • Scab treatments run from bloom through spring.
  • Leaf blight treatments starts at early leafing and continues through petal fall.

Estimating bloom stages is a matter of visual scanning of the orchard. Use the photos and descriptions below to familiarize yourself with the various bloom stages.

Pink bud stage of reproductive growth of almond.

Pink bud stage

Popcorn stage of reproductive growth of almond.

Popcorn stage

10% bloom

At 10% bloom approximately 1 out of every 10 blossom buds is open. To check for this stage, look at a series of tree branches throughout your orchard. Do you see an average of 1 open blossom for every 10 closed ones on a branch?

Full bloom stage of almond bloom.

Full bloom

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. During 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%.

Petal fall stage of almond bloom.

Petal fall

At petal fall, most of the blossoms in the orchard have dropped their petals and only sepals, styles, stigmas, and stamens are left.

Post petal fall

At post-petal fall stage a majority of the sepals (calyx, shuck) on the remains of flower blossoms are dry, senescing, and turning brown.

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