Dealing with Fruit Tree Pests and Diseases

Many of us dream of picking an apple in our own back yard.  Just as you go to take a bite, you notice a few brown spots on the skin as well as an entry hole.  Such disappointment after so much work!

Apple trees are susceptible to several pests and diseases.  Below, we will list the potential problems and solutions.

Fungal diseases:

Apple scab

Apple scab is a prevalent fungal disease affecting apple and crabapple trees. It causes unattractive spots along leaf veins, which eventually turn black and make the whole leaf yellow. Fruit infected by apple scab develop olive-green spots that gradually become brown and cork-like.

The fungus survives the winter on fallen fruit and leaves, making it essential to clear away all fruit and leaf debris in the fall to prevent spreading the disease to new leaves in the spring.

Powdery Mildew

Apple tree powdery mildew is a fungal disease that appears as white, powdery spots on new leaves, shoots, and fruit. It causes stunted growth, leaf curling, and russeted fruit. The fungus thrives when daytime temperatures are warm, humidity is high, and nights are cool. To manage it, prune infected shoots and apply sulfur or fungicides between the tight cluster stage and bloom.

Fungal Disease Control

Removing leaves and fallen fruit disrupts the fungal disease cycle; if left, rain can spread spores back into the tree. Dormant oil helps prevent overwintering insects and disease—see below for application details.

Bacterial infections:

Fire blight

Fire blight is a highly contagious and destructive bacterial disease capable of destroying blossoms, shoots, and even entire apple trees within a single season. The pathogen exhibits peak activity during warm, humid spring conditions and outbreaks are frequently observed following events such as hail or strong winds that produce entry wounds on the trees.  

If fire blight is detected, it's crucial to remove the affected areas by pruning. Be sure to prune during dry conditions, cutting at least 8-12 inches below any visible signs of infection. After each cut, sanitize your tools with 70% rubbing alcohol to avoid spreading the bacteria.

Avoid excessive nitrogen fertilizer, which encourages succulent new growth that is highly susceptible to infection.

Copper sprays can be used as a delayed-dormant treatment (before buds open) to reduce surface bacteria.

Pests:

Coddling Moth

The codling moth is a significant agricultural pest, best known for its larvae, which are commonly referred to as the "worm in the apple." These larvae penetrate fruit to consume the seeds, resulting in internal decay and premature ripening. If not properly managed, infestations can lead to losses of up to 90% of the crop.  Larvae tunnel to the core to eat seeds, leaving behind reddish-brown, crumbly droppings called frass at the entry or exit hole.

Control - Guardian for Orchards nematodes:

Coddling moth spends part of its life cycle as larvae in the soil. This soil-dwelling stage makes them susceptible to entomopathogenic nematodes (EPN).  Codling moth (1-2 generations per year) have larvae or pupae that overwinter in soil, tree bark, or crevices. Their most vulnerable stage to entomopathogenic nematodes (EPN) occurs when larvae exit fruit or establish in the soil, typically lasting 2-4 weeks. Recommended control involves two applications, one by mid May for overwintered larvae and the second in early to mid August for new larvae exiting fruit.

It is strongly recommended to couple the use of nematodes with Codling Moth traps 

 Apple maggot—mid May to end of May for overwintering pupae and mid August/mid September for larvae
entering the soil.
 Peachtree borer—May for overwintered larvae and mid August/mid September for the new generation.
Visual indicators include fruit drop with entry holes (codling moth, western cherry fruit fly, apple maggot), crescent-
shaped scars on small fruit (plum curculio), and gummy exudate with frass at the tree base (peachtree borer).

Apple Maggots

The apple maggot  or "railroad worm," is a destructive North American fruit fly that targets apples. The small adult lays eggs under the fruit's skin; after hatching, larvae tunnel through the flesh, causing rot, dimpling, and early fruit drop.

Control for Apple Maggot:

Apple maggot can also be controlled using Guardian for orchards.  Application should be mid May to end of May for overwintering pupae and mid August/mid September for larvae entering the soil.

Notes on Guardian for Orchards:

• Store Guardian for Orchards at 5-7°C (41-45°F) for up to 12 weeks; do not freeze.
• Remove old leaves from under trees for better soil penetration; Water soil before application and lightly for 3-4 days after; Ensure soil temperature is at least 10°C
  (50°F); Apply in shade, cloudy weather, or late afternoon.
• Do not mix with fertilizers or pesticides.
• Wet soil to 5-8cm (2-3 in) depth
• 
  Application
• Sponge contains 10M nematodes; Soak sponge in 1L (0.26 gal) water, wring out sponge 5-10x, rinse packaging.
• 1L concentrate treats 40m² or 400ft2 (4 trees);
• Stir between refills: Use prepared suspension within 2 hours: Apply using NIC’s Hose End Sprayer (1:80 dilution)

Conclusion

It's always best to combat orchard pests in more than one location and life stage. We suggest using a trap and lure systems in conjunction with nematodes to get the best possible results.

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