Scab (Gummosis)

Pseudomonas syringae

1 host plant

Last updated

Data Maturity Baseline

This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.

Scab and gummosis appear as lesions and gum exudation on fruit and branches. This fungal disease spreads in wet conditions. Remove infected material. Improve air circulation and reduce leaf wetness. Apply fungicides preventively during vulnerable periods. Monitor your plants closely and implement integrated management strategies. Prompt removal of infected material helps limit disease spread Early detection and prompt management of symptoms help limit disease spread.

Scab management starts in fall: rake up and destroy infected fallen leaves, which are the primary source of spring spores. Resistant cultivars eliminate the problem entirely for new plantings. For existing susceptible trees, fungicide applications beginning at bud break and continuing through petal fall protect new foliage during the critical infection window. Proper timing matters more than product choice.

Quick Reference

Causal Agent
Pseudomonas syringae
Host Plants
1

Management

Cultural Controls

  • Avoid overhead irrigation; use drip irrigation or soaker hoses to keep foliage dry
  • Prune in dry weather; sterilize tools between cuts with 10% bleach solution or alcohol
  • Remove infected branches, cankers, and frost-damaged wood that serves as disease entry point
  • Avoid spring pruning; prune in late fall or winter to avoid frost crack vulnerability
  • Improve air circulation through selective pruning to reduce humidity and drying time after rain

Host Plants (1)