Diseases

Bacterial canker

Pseudomonas syringae

Overview

  • Primarily a disease of sweet cherry, tart cherries less susceptible
  • Site, management, variety selection, and copper application are primary control strategies

Symptoms

  • Cankers on trunk, limbs, and branches exude gum during spring and summer
  • Leaves discolor and wilt on affected branches
  • Leaf and fruit infection can occur when serious, as evidenced by necrotic spots, leaf yellowing, and/or water-soaked necrotic tissue on fruits
  • Infected flower buds can fail to open in spring or result in rapid die-back browning of flowers/fruit/foliage

Disease cycle

  • Bacteria over-winter on tree in canker margins, healthy buds, and in vascular system
  • Bacteria multiply in spring and spreads during rainfall
  • Wet, cool springs with frost or storms that damage blossom and leaf tissue favor outbreaks
  • Bacteria can survive symptomless on leaves from bloom through leaf fall, whereupon infects fresh leaf scars and overwinters 

Management

  • Apply high rate copper in spring just before bud-break and in fall after leaf drop
  • Avoid pruning in spring during wet weather; apply copper immediately after pruning
  • Prune in summer after harvest
  • Discard nursery stock at planting if any sign of bacterial canker present

More information

 

Brown rot

Monilinia fruiticola

Overview

  • American brown rot is an important fungal disease of cherries
  • Without control, and under wet conditions, partial to complete fruit loss can occur as a result of brown rot

Symptoms

  • Brown rot affects blossoms, spurs, shoots, and fruit but fruit infections are most destructive
  • As cherry fruit mature, they are more likely to become infected, developing light brown spots which eventually take over the whole fruit and give it a fuzzy brown appearance and eventually rotting the fruit

Disease cycle

  • Source of infection in cherry is primarily overwintering inoculum in fruit mummies, peduncles, and cankers
  • Wind-driven rain in the spring infects blossoms, depending on the duration of wetting and temperature
  • Fruit infection can occur through the cuticle, or more easily in natural openings and wounds; rain-cracked cherries are brown rot's best friend!
  • Level of inoculum drives infection severity, so once brown rot gets going and it is wet stand back! Or spray fungicide...

Management

  • Sanitation - remove non-harvested, mummified cherries if possible; keep orchard floor clean
  • Fungicides - beginning at bloom, 2 or 3 sprays (often overlooked) and then resuming as fruit ripens; timing and frequency depends on weather/wetting and condition of crop, but in most years several fungicide sprays are necessary during pre-harvest and harvest; be sure to rotate fungicides to prevent resistance development
  • Sweet cherries are generally more susceptible to brown rot than tart cherries; otherwise, there is very little difference in variety susceptibility

Special note on European brown rot (Monolinia laxa). European brown rot may be present in New England on tart cherry, however, it has not been confirmed. It is common in the midwest and has been reported in New York. The main difference between American and European brown rot is European is far more aggressive infecting blossoms and spurs, resulting in blight/dieback of blossoms and spurs. It's not pretty. It can be confused with bacterial canker. Two sprays, one at popcorn bud stage and then another 7 days later are recommended on all tart cherry. Resistance may be an issue.

Cherry leaf spot

Blumeriella jaapii

Overview

  • Can be a significant problem when inoculum builds on cherries grown in humid climates
  • Lack of control can cause premature leaf drop and declined winter hardiness
  • Sweet cherry generally less susceptible to cherry leaf spot than tart cherry, when it can become severe!

Symptoms

Disease cycle

  • Overwinters on leaves on orchard floor (think apple scab)
  • Spores discharged, ideal temperature 60 to 85 F., triggered by rain, beginning at bloom to 6 weeks after petal fall
  • Very similar to apple scab, varying hours of leaf wetness, depending on temperature, required for infection
  • Continued spread by conidia on infected leaves continues with wetting

Management

  • Sanitation by removal/chopping/decomposition of leaf litter should help, as well as good season-to-season control
  • Otherwise, fungicide applications beginning at petal fall (or first leaves) and continuing every 7 to 10 days until harvest, followed by 2 post-harvest applications
  • Tart cherries require more aggressive fungicide application schedule (including post-harvest) than sweet cherry, particularly during wet seasons