Pear blossom blast and dieback (Pseudomonas syringae) (BIOFRUITNET Practice Abstract)

Summary

Less dieback of blossoms and a better yield when the bacterium is controlled.
Practical recommendation
The bacterium Pseudomonas is present on many plants including woody and herbaceous plants. Pseudomonas are epiphytic (organism that grows on the surface of a plant/tree). Epiphytic overwintering in the buds of pear is possible. If weather conditions (i.e., rainy, cold) are favourable for the bacterium, it will grow fast and cause damage. In pear, rain and low temperatures, especially frost-inducing temperatures during bloom, increase the incidence of blossom infection. Blossom petals are very susceptible.
Preventive measures
• No over-crown irrigation when not necessary,
• Over-crown irrigation only in case of frost protection, and
• Prune away infected parts.
Direct control measures
• Protect blossoms during cold weather conditions,
• Copper products, two-three sprays in spring (when allowed),
• Alternative products could be Blossom Protect (Aureobasidium pullulans), Bacillus subtilis and B. amyloliquefaciens. Some growers use a laminarin product.
Diagnosis of Pseudomonas - confusion is possible with
• Fireblight (Erwinia amylova): There is a difference in the conditions for infection: fireblight needs warm temperatures and Pseudomonas prefers rainy, cold conditions. Moreover, the first symptoms of Pseudomonas are small, black spots on the flower petals.
• Alternaria spp. (dead flower buds): Symptoms are a partial or complete necrosis of flower buds during dormancy or bud break.