Apple scab is caused by the fungus Venturia inaequalis. It infects crabapples and apples (Malus spp.), mountain ash (Sorbus spp.), pear (Pyrus communis) and Cotoneaster (Cotoneaster spp.).
Seeing brown leaves on your apple tree can be worrying But don’t panic – brown leaves are common and usually easy to treat. This comprehensive guide explores all the reasons apple leaves go brown, and how to nurse your tree back to health
Overview of Main Causes
Apple tree leaves can turn brown due to
- Underwatering (most common)
- Overwatering
- Weather and climate stress
- Nutrient deficiencies
- Diseases like fire blight
- Pests such as aphids and apple maggots
Inadequate water is the most frequent culprit. But properly diagnosing the specific cause is key, as treatment varies. We’ll now delve into each factor in detail.
Insufficient Water
Apple trees need consistent moisture. If soil gets too dry, leaves lose turgor pressure and dehydrate. Initial symptoms are curled, wilted leaves. Prolonged drought causes browning.
Solutions for Underwatering:
- Check soil moisture before watering. Ideally use a moisture meter.
- Water when top 2-4 inches become dry. Deeply soak the root zone.
- Mulch around tree to retain moisture and reduce water needs.
- Consider irrigation if rainfall is inconsistent. Drip irrigation works well.
Overwatering
Excess moisture also causes problems. Soggy soil leads to root rot and oxygen deprivation. Leaves yellow and drop prematurely.
Fixes for Overwatering:
- Ensure pot or ground has drainage holes and amend clay soils.
- Check drainage by pouring water in a hole and timing percolation rate.
- Allow soil to partially dry out between waterings.
- Reduce watering frequency and quantity.
Getting the watering balance right is crucial for healthy leaves
Weather Stress
Temperature extremes, frost, high winds and other weather events can scorch or dehydrate leaves, causing browning. Young trees are especially vulnerable.
Protecting Trees from Weather:
- Shelter trees from harsh sun and wind, especially newly planted ones.
- Ensure correct chill hours for your variety. Most need 400-1000 hours under 45°F.
- Mulch and irrigate to protect roots from temperature swings.
- Consider growing in a greenhouse or indoors if climate is unsuitable.
While apple trees resist brief cold snaps, extreme heat causes more problems.
Nutrient Deficiencies
Lack of nitrogen, iron, zinc, manganese and other nutrients turns leaves yellow then brown. Deficiencies show in youngest leaves first.
Preventing and Correcting Deficiencies:
- Test soil pH – apple trees prefer slightly acidic around 6.0-6.5.
- Use a complete balanced fertilizer when growth begins in spring.
- Identify specific deficiencies by leaf color patterns. Target fertilizers accordingly.
- Apply zinc sulfate, iron chelate, epsom salts or other amendments.
- Mulch trees annually with 2-4 inches of compost.
Routine fertilization and pH monitoring prevents most deficiencies. Fast-acting liquid fertilizers can provide a quick fix.
Fire Blight
The bacterial disease fire blight is a prime cause of apple leaf browning. Symptoms include:
- Leaves brown and blacken but remain attached to branches.
- Infected branches bend into a shepherd’s crook shape.
- Leaves look scorched.
- Ooze may be present on bark.
Managing Fire Blight:
- Improve air circulation and prune out infected branches.
- Apply copper sprays as dormant spray and during bloom when infection risk is high.
- Remove any wild host plants like pyracantha and hawthorn.
- Choose resistant cultivars like Haralson, Liberty and Honeycrisp.
Early intervention is key, as fire blight spreads rapidly. Severely infected trees may need removal.
Pests
Hungry insects like aphids, leafrollers and maggots can skeletonize and damage leaves. Heavy infestations cause browning. Other signs include sticky honeydew and webbing.
Controlling Apple Tree Pests:
- Check undersides of leaves regularly and identify pests.
- Apply insecticidal soap, neem oil or appropriate pesticide.
- Attract beneficial insects like ladybugs and lacewings.
- Use pheromone traps and bait stations for some pests.
- Remove dropped fruit immediately to prevent maggots.
Prevention with row covers and tree collars is ideal. Monitor young trees closely.
Other Causes
- Improper pruning – Overpruning stresses the tree. Bad technique creates disease entry points. Follow best practices.
- Root damage – Restricted roots from girdling, rodents or root rot reduce nutrient uptake. Examine roots and soil for issues.
- Transplant shock – Newly transplanted trees experience stress. Allow time to establish and water diligently.
- Incorrect planting – Problems like deep planting stress the tree. Plant at same level as nursery container.
- Pollution – Environmental toxins like salt and car exhaust damage leaves. Wash leaves and improve air quality.
- Age – Older trees naturally shed more leaves. As long as it’s not excessive, it’s usually normal.
While less common, these factors can contribute to apple leaf problems. Careful inspection reveals clues to the cause.
When to Worry About Brown Leaves
Mild leaf drop is normal in fall and causes little concern. But take notice if:
- Browning is excessive or affects the entire canopy.
- It occurs on younger leaves or during the growing season.
- Tree has other symptoms like stunted growth or branch dieback.
- You find evidence of pests, disease, or nutrients issues.
Seeking expert diagnosis may be prudent if browning is advanced or causes exist outside the tree’s control, like weather extremes.
Final Tips for Healthy Leaves
- Select suitable cultivars for your climate. Most do best in zones 3-9.
- Give trees ample sun – at least 6 hours of direct sun daily.
- Space trees appropriately – standard trees 20-30 feet apart.
- Control weeds and grass that compete for water and nutrients.
- Whitewash trunks of young trees to prevent sunscald.
- Clean up diseased leaf litter and fallen fruit around trees.
With proper care, you can enjoy an apple tree with vibrant foliage for years to come. Stay vigilant for early symptoms of problems, and take prompt corrective action for best results.
How to identify apple scab Advanced apple scab on a leaf
- Leaf spots are round, olive-green, and up to 1/2 inch across.
- Spots are velvet-like with fringed borders.
- As they age, leaf spots turn dark brown to black, get bigger and grow together.
- Leaf spots often form along the leaf veins.
- Leaves with many leaf spots turn yellow and drop by mid-summer.
- Infected fruit have olive-green spots that turn brown and corky with time.
- Fruit that are infected when very young become deformed and cracked as the fruit grows.
Life cycle of apple scab Corky apple scab on fruit Older infections turn black, then leaves turn yellow and fall off.
The apple scab fungus has several host-specific strains that can cause disease on one type of plant but not any other. For example, the strain of V. inaequalis that infects mountain ash will only infect other mountain ash trees and will not infect crabapple trees. Apple and crabapple trees are infected by the same strain of the apple scab fungus because the trees are in the same genus.
- The apple scab fungus overwinters on fallen diseased leaves.
- In spring, these fungi shoot spores into the air.
- Spores are carried by wind to newly developing leaves, flowers, fruit or green twigs.
- Spores need several hours of moisture on the plant surface to start new infections.
- These infections grow into spots that can produce more spores within 9 to 17 days.
- Spores are spread by wind, splashing rain or irrigation throughout the tree canopy or to neighboring trees, starting new infections.
- The infection cycle can repeat many times throughout the growing season whenever leaves remain wet long enough.
- Warm, rainy weather in the spring and summer creates ideal conditions for apple scab.
- Leaves with many leaf spots turn yellow and fall off early. This weakens the tree.
- Several years of early leaf loss can result in decreased growth, reduced bloom and increased susceptibility to winter injury.
- Many ornamental crabapple trees are susceptible to apple scab, so the disease can be spread to your fruit trees from nearby flowering crabs.
Avoiding Fire Blight | Save your Pear (& Apple) Trees from this Deadly Disease
FAQ
What to do when apple tree leaves turn brown?
When apple tree leaves turn brown, it could be due to various factors such as disease, pests, or environmental issues. Identifying the specific cause is crucial for effective treatment. Possible causes include apple scab, fire blight, cedar-apple rust, fungal infections, or nutrient deficiencies.
How do you treat brown leaves on trees?
- Cause: Dry soil and drought.
- Solution: Water the tree.
- Cause: Overly moist soil.
- Solution: Assess your watering schedule.
- Cause: Limited or damaged root system.
- Solution: Time and adequate watering.
- Cause: Fungal or bacterial diseases.
- Solution: Call in a professional.
How to treat brown patches on apple tree leaves?
The best thing to do is to always rake up any fallen leaves around the apple trees and/or prune select branches to open up the canopy for air flow to keep the leaves dry. You can spray a fungicide as a preventative measure or choose apple varieties that are resistant to the disease.
Can a dying apple tree be saved?
“The apple tree can be saved,” he declared. The fact it has new growth is a good sign, and likely a good pruning will go far in bringing it back to health, Kuehn added. The best time to cut it back, he advised, is when the tree is not growing – sometime in February or March.