Fruit trees are cherished for their beauty and bountiful harvests, but they are susceptible to various diseases that can compromise their health and productivity. In the Pacific Northwest, the humid climate fosters conditions favorable to both fungal and bacterial pathogens. Understanding these common diseases and implementing effective organic management strategies is crucial for maintaining a thriving orchard.
Anthracnose (Perennial Canker/Bull's Eye Rot)
Anthracnose and bull’s-eye rot are significant diseases in apple and pear orchards, and it is quite common on Vancouver Island. These pathogens cause sunken, discolored bark cankers and fruit rot, with telltale concentric bull’s-eye patterns. The disease thrives in wet conditions, spreading via rain splash and overwintering on infected plant material.
Symptoms:
Bark cankers that enlarge over time.
Rotting fruit with concentric rings resembling a bull’s-eye.
Premature leaf drop in severe cases.
Organic Management:
Pruning:
Remove diseased branches and cankers pruning at least 6–8 inches below visible symptoms, making sure to use sterilized tools to prevent spread.
Dispose of infected wood and plant debris either by burning or double bagging and sending to the dump as these are reservoirs for pathogens. DO NOT COMPOST!
Biological and Organic Controls:
Copper-based fungicides are effective against anthracnose when used as part of an integrated pest management (IPM) plan.
Use biological treatments like Effective Microorganisms to outcompete the bacteria.
Orchard Sanitation:
Rake and remove fallen leaves, fruit, and other debris to eliminate fungal spores. DO NOT COMPOST!
Post-Harvest Practices:
Store harvested fruit in cool, dry environments to prevent rot from developing.
Inspect stored fruit regularly for signs of infection and remove affected items promptly.
Cultural Practices:
Encourage tree health with proper fertilization, irrigation, and mulching as a healthy tree is the best defence.
Ensuring proper tool sanitization between cuts and between trees to prevent spread.
Avoid wounds or injuries to trees, as these are entry points for the fungus.
Space trees properly and thin canopies to promote airflow and reduce humidity, which limits fungal development.
Black Knot
Black knot is a fungal disease affecting stone fruits such as cherry and plum trees, forming hard, black galls on the trunk, branches and twigs. It can severely impact tree health and productivity if left untreated. It is highly transmissible and can spread through windborne spores during wet conditions.
Symptoms:
Swollen, black, rough galls on the trunk, twigs and branches.
Progressive branch dieback in severe cases.
Organic Management:
Pruning:
Prune infected branches about 6–8 inches below the visible galls. It is best to do this during tree dormancy when the branches are visible (late fall or winter).
Make sure to sterilize pruning tools between cuts with isopropyl alcohol or a light bleach solution to prevent bacterial spread.
Orchard Sanitation:
Dispose of infected wood and plant debris either by burning or double bagging and sending to the dump as the fungus can still spread once pruned off the tree. DO NOT COMPOST!
Resistant Varieties:
Plant resistant cultivars when possible to minimize susceptibility.
'Shiro', 'Stanley' and 'President' are all more resilient against black knot.
Cultural Practices:
Improve airflow through proper tree spacing and canopy thinning.
Avoid unnecessary injuries to trees, as wounds provide entry points for the fungus.
Biological and Organic Controls:
Spray the affected area with a sulfur or copper based organic fungicides as a preventative in early spring. (March/April)
Use biological treatments like Effective Microorganisms to outcompete the bacteria.
Fire Blight
Fire blight is a bacterial disease that primarily affects apples, pears, quince and other related species. It manifests as blackened, scorched-looking shoots, cankers on branches, and oozing bacterial lesions, spreading rapidly during warm, humid weather through rain, insects, and tools.
Symptoms:
Wilted, blackened shoots resembling fire damage.
Oozing cankers on branches and trunks.
Rapid dieback of branches and flowers.
Organic Management:
Pruning:
Remove infected branches during dry weather, cutting 12–18 inches below visible symptoms and making sure to sterilize pruning tools between cuts with alcohol or a bleach solution.
Resistant Varieties:
Plant apple and pear cultivars that use resistant rootstocks or have been bred for resistance to fire blight.
'Liberty', 'Enterprise' and 'Freedom' are resistant apple varieties and 'Harrow Delight', 'Moonglow' and 'Magness' are resistant pear varieties.
Cultural Practices:
Avoid excessive nitrogen fertilization, which encourages lush, vulnerable growth.
Properly space trees and thin canopies to promote airflow and reduce humidity.
Biological and Organic Controls:
Apply organic bactericides such as copper-based sprays during bloom.
Use biological treatments like Effective Microorganisms to outcompete the bacteria.
Integrated Pest Management (IPM):
Monitor closely during bloom, as infections often start on flowers.
Remove and burn severely infected branches when necessary to prevent the spread.
Bacterial Canker
Bacterial canker affects stone fruits like cherries, plums, and apricots, causing sunken, dead bark areas, oozing sap, and dieback of branches. It thrives in wet, cool conditions and can enter trees through wounds or natural openings.
Symptoms:
Sunken, darkened cankers on bark.
Gummy sap (gummosis) oozing from infected areas.
Wilted or dying branches.
Organic Management:
Pruning:
Prune infected branches during dry weather, cutting 6–8 inches below symptoms.
Make sure to sterilize pruning tools between cuts with isopropyl alcohol or a light bleach solution to prevent bacterial spread.
Avoid pruning during wet or cool conditions to reduce infection risk.
Biological and Organic Controls:
Apply copper-based sprays during dormancy and after pruning to suppress bacterial populations. Reapply after heavy rains to maintain coverage.
Use biological treatments like Effective Microorganisms to outcompete the bacteria.
Cultural Practices:
Encourage tree health with proper fertilization, irrigation, and mulching as a healthy tree is the best defence.
Ensuring proper tool sanitization between cuts and between trees to prevent spread.
Avoid wounds or injuries to trees, as these are entry points for the fungus.
Properly space trees and thin canopies to promote airflow and reduce humidity.
Resistant Varieties:
Plant resistant cultivars and rootstocks when possible to minimize susceptibility.
'Lapins' cherry and 'Shiro' plum are both more resistant to bacterial canker.
Orchard Sanitation:
Remove and dispose of fallen leaves and pruned material to eliminate spread. DO NOT COMPOST!
Apple and Pear Scab
Apple and pear scab are fungal diseases that cause olive-green to black spots on leaves, fruit, and young shoots, leading to defoliation, reduced fruit quality, and lower yields. These pathogens thrive in humid, wet conditions and overwinter on fallen leaves.
Symptoms:
Velvety, dark lesions on fruit and leaves.
Premature leaf drop in severe infections.
Organic Management:
Pruning:
Prune to improve airflow and sunlight penetration by thinning the canopy which will reduce humidity.
Remove and destroy infected branches and leaves.
Orchard Sanitation:
Rake and compost fallen leaves or dispose of them to eliminate overwintering spores. DO NOT COMPOST!
Resistant Varieties:
Plant resistant cultivars to minimize disease risk such as 'Liberty', 'GoldRush', and 'Enterprise' apples and 'Harrow Sweet', 'Harrow Delight' and 'Moonglow' pears.
Biological and Organic Controls:
Apply sulfur or copper during key growth stages such as pre-bloom and early fruit development.
Cultural Practices:
Avoid overhead watering to minimize wet conditions on foliage.
Properly space the trees when planting.
Leaf Curl
Leaf curl is a fungal disease that affects stone fruits such as peaches, nectarines, almonds, plums and cherry. This disease distorts, puckers, and discolored leaves, often leading to defoliation and reduced fruit yields. Wet, cool conditions during spring favor its development.
Symptoms:
Red, thickened, distorted leaves.
Premature leaf drop and poor fruit production.
Organic Management:
Biological and Organic Controls:
Use organic copper or lime sulfur sprays during the dormant season to kill overwintering spores.
Orchard Sanitation:
Remove and destroy infected leaves promptly to reduce spore spread.
Resistant Varieties:
Choose resistant cultivars to minimize disease occurrence such as 'Frost', Q-1-8', and 'Avalon Pride' peach and nectarines.
Cultural Practices:
Encourage tree health with proper fertilization, irrigation, and mulching as a healthy tree is the best defence.
Space trees properly and thin canopies to promote airflow and reduce humidity, which limits fungal development.
Grow against a south-facing wall or under a roof overhang to avoid excess moisture.
Avoid overhead watering, drip irrigation is best.
Shot Hole Disease (Coryneum Blight)
Shot hole disease is a fungal infection that affects stone fruits like cherries, peaches, and plums. It manifests as small, round lesions on leaves, fruit, and twigs that eventually fall out, leaving a "shot hole" appearance. The disease thrives in wet conditions and can reduce tree health and fruit quality.
Symptoms:
Circular lesions on leaves, fruit, and shoots.
Holes where lesions drop out.
Organic Management:
Pruning:
Prune infected branches during dormancy.
Prune tree shape to improve airflow and sunlight penetration by thinning the canopy which will reduce humidity.
Orchard Sanitation:
Rake and destroy fallen leaves to eliminate overwintering spores. DO NOT COMPOST!
Biological and Organic Controls:
Apply organic copper-based sprays, during dormant and pre-bloom stages.
Cultural Practices:
Space trees properly and avoid overhead watering to minimize leaf wetness.
Powdery Mildew
Powdery mildew is a common fungal disease affecting nearly all fruit trees, causing a white, powdery coating on leaves, shoots, and fruit. It can stunt growth, reduce fruit quality, and weaken trees if unmanaged.
Symptoms:
White, powdery fungal growth on foliage and young shoots.
Stunted or distorted growth.
Organic Management:
Pruning:
Remove infected shoots to reduce spore sources.
Thin canopies to improve airflow and reduce overall humidity.
Orchard Sanitation:
Rake and remove fallen leaves to eliminate overwintering spores.
Only hot compost affected leaves to destroy spores before reapplying to garden.
Biological and Organic Controls:
Use organic sulfur-based or potassium bicarbonate fungicides during key growth stages.
Use diluted milk or whey (1:10 ratio with water) as a natural antifungal spray.
Use biological treatments like Effective Microorganisms to outcompete the bacteria.
Cultural Practices:
Avoid over-fertilizing to prevent excessive, vulnerable growth.
Brown Rot
Brown rot is a fungal disease that affects all fruits but specifically targets stone fruits like peaches, cherries, and plums. It causes blossom blight, twig cankers, and rotting fruit covered in tan spore masses, significantly reducing fruit quality and tree health.
Symptoms:
Brown, rotting fruit with spore masses.
Blighted blossoms and twig dieback.
Organic Management:
Pruning:
Improve airflow by thinning the canopy and removing cankers during dormancy.
Prune tree shape to improve airflow and sunlight penetration by thinning the canopy which will reduce humidity.
Biological and Organic Controls:
Apply sulfur or copper-based sprays during bloom and pre-harvest periods to prevent infections.
Orchard Sanitation:
Remove infected twigs, blossoms, leaves and mummified fruit during dormancy. Properly dispose of all debris to eliminate fungal spores.
Only hot compost affected fruits to destroy spores.
Do not allow affected fruits to drop and rot in place.
Encourage tree health with proper fertilization, irrigation, and mulching as a healthy tree is the best defence.
Fruit tree diseases can be a challenge, but with the right knowledge and organic strategies, maintaining a healthy and productive fruit tree is achievable.Combining cultural practices, organic controls, and resistant cultivars can make a significant difference. Regular monitoring, proper sanitation, and timely interventions are key to success.
If you are looking for a tree diagnosis or help with disease management, I offer skilled fruit tree pruning and consultation services. Book now!