Understanding Almonds: Full Bloom Diseases

Almond growers know full bloom means taking the right steps to maximize yield. Making the most of the season requires proactive protection from full bloom diseases that impact nut set and quality.

“Achieving a healthy nut set is critical to a strong yield,” said Dawn Brunmeier, Technical Service Representative, BASF. “Spur dynamics, flower density, environmental conditions and overall tree health all impact set. Growers should control what they can, and protect against what they cannot.”

Growers cannot control rain, but they can apply fungicides preemptively to prevent disease outbreaks during full bloom – many diseases’ favorite time to attack. Several diseases are quick to return or can leave a lasting impact on tree health, which makes controlling them a matter of protecting a long-term investment.

Here are a few of the diseases that can strike almond trees during full bloom:
Brown Rot

  • Ideal Conditions: requires moisture and attacks most when flowers are fully open, which makes rain during bloom-time a breeding ground for the fungus.
  • Identification: flower collapse and shoot blight, gum exuding at the base of infected flowers, cankers on blighted twigs and spore masses on infected flowers and twigs.
  • Damage: kills the woody tissues within a tree, causing a “canker” that kills the branch and provides a place for the fungus to thrive. These cankers are the epicenters of brown rot that make it extremely difficult to rid an orchard of the disease following a widespread infection.

Jacket Rot

  • Ideal Conditions: cool and wet conditions during bloom can manifest into a green fruit rot, or jacket rot, in the latter part of bloom. Extended bloom periods with wet weather are most likely experience jacket rot.
  • Identification: water-soaked brown spots on blossom petals. Infections can spread to flower jackets causing them to stick to developing nuts.
  • Damage: as nuts set and start to grow, infections from bloom can cause a brown spot to develop on the jacket causing it to stick to the nut. This can infect entire nut clusters if flower parts are trapped.


  • Ideal Conditions: favors humid environments and will become worse when rain occurs. Orchards by water sources beware!
  • Identification: small yellow dots it produces on the upper leaf surface, or rusty red pustules on the lower leaf surface. The disease never attacks fruit, but can sometimes make its way to younger twigs.
  • Damage: preventing and treating for rust is imperative, as the fungus can thrive from one year to the next in infected leaves.


  • Ideal Conditions: favors prolonged wet spring weather and is often found in orchards that use sprinkler-irrigation systems.
  • Identification: presents as greasy black spots on leaves, fruit and twigs.
  • Damage: was not always considered a crop-threatening disease, but while it does not cause apparent damage to fruit, it can cause a tree to become weakened and even lose all of its leaves in a short period of time.

Shot Hole

  • Ideal Conditions: occurs in wet years with extended rainfall or sprinkler-irrigated orchards, as it requires water for all its activities.
  • Identification: most often produces lesions on leaves as they emerge from the leaf bud, but can also occur on flowers, fruits and twigs.
  • Damage: causes defoliation of leaves and fruit, loss in yield and weakened trees.

Knowing which fungicides to use, and when to use them, is key to preventing full bloom diseases. Merivon® fungicide from BASF protects almond blossoms from various disease pressures to increase yield and profitability.
Disease prevention both improves fruit quality and extends tree life. Merivon fungicide, extends its work by creating reservoirs on leaf surfaces that continually distribute its protective chemistry throughout the leaf to provide long-lasting disease protection. It also moves systemically in the crop, protecting areas untouched by the initial application.
The long-lasting disease protection and Plant Health benefits of Merivon fungicide protect and heal, boosting the strength of the tree to create healthier, higher-quality almonds for years to come.
To learn more, visit www.GrowSmartAlmonds.com or contact your local BASF representative.