Dead flower buds of pear: effect of tree growth control, and Alternaria alternata as causal agent.

Dead (dormant) flower buds of pear is an important phenomenon in pear production in the Netherlands. Vigourous or unbalanced tree growth and Pseudomonas syringae pv. syringae are mentioned as likely causes of dead flower buds. Several tree growth control treatments including ethephon. Regalis (Prohexadione-Ca) and root pruning were evaluated. Regalis increased disease incidence. The plant stimulant (foliar fertilizer) Resistim (potassium phosphonate) reduced disease incidence. Pseudomonas syringae pv. syringae was occasionally isolated from diseased flower buds. However, Alternaria alternata was nearly always isolated from diseased buds. Indicating a strong relation between this fungus and dead flower buds of pear.