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Apple trees are amazing assets to the home landscape and orchard, but when things start to go wrong, its often a fungus thats to blame. Black rot in apples is a common fungal disease that can spread from infected apple trees to other landscape plants, so its important to watch your apple trees for signs of black rot disease in order to catch it early in the disease cycle. Distressing as it is, when block rot attacks your apple trees, its not the end of the world. You can get your apples back and have healthy harvests if you understand how to destroy the disease.
Black rot is a devastating fungal disease that affects apple trees. It can lead to serious crop losses if left unchecked. As a home gardener or commercial orchardist, it’s crucial to understand this disease and how to effectively treat it. In this comprehensive guide, we’ll cover everything you need to know about managing black rot in apple trees.
What Causes Black Rot in Apples?
Black rot is caused by the fungus Botryosphaeria obtusa. This fungus can infect apples and some other fruits like pears and quinces. On apples, it primarily affects the fruit, leaves, and branches. The fungus overwinters in old cankers on branches and twigs as well as in mummified fruits that remain on the tree. In spring, spores are released from these overwintering sites and spread the disease.
Wet, humid conditions favor the development of black rot Temperatures above 48°F allow the fungus to grow Infections often begin after rain or heavy dews. The optimum temperature for spore germination and infection is between 75-80°F.
Symptoms of Black Rot
On Fruit
- Large, brown, rotten spots on the fruit, especially at the blossom end
- Concentric rings of brown/black tissue in lesions
- Fruit mummies shrivel and remain on tree
- Small black fungal fruiting bodies may be visible in lesions
On Leaves
- Circular spots with purple/reddish border and tan center (“frog eye” appearance)
- Heavily infected leaves turn yellow and may drop
On Branches
- Sunken, reddish-brown cankers with rough, cracked bark
- Dieback of infected branches
Treatment and Control
Treating black rot requires an integrated approach:
Sanitation
- Remove any mummified fruit – these harbor spores
- Rake up and dispose of fallen leaves and debris
- Prune out dead, damaged, or diseased wood
Pruning
- Prune trees during dormancy before spring growth
- Remove cankers by cutting 6+ inches below visible infection
Tree Health
- Select resistant varieties
- Plant in appropriate sunny site with well-drained soil
- Water during drought to reduce stress
- Control pests like fire blight that weaken trees
Protective Sprays
- Apply copper-based fungicide at green tip through bloom
- After petal fall, use captan, sulfur, or other labeled fungicide
- Ensure thorough coverage of leaves, fruits, and twigs
Timing Treatments
- Green tip stage: Apply first copper spray for early protection
- Bloom: Continue protective sprays every 7-10 days
- Petal fall: Switch to captan, sulfur, or other fungicide
- Continue sprays every 7-14 days until harvest
- Inspect trees regularly and remove diseased wood promptly
Promptly treating any infections is crucial for saving trees and their fruit crops. With vigilance and a proactive treatment approach, black rot can be successfully managed. Combining cultural practices like sanitation and pruning with protective sprays offers the best protection against this harmful apple disease.
FAQs about Black Rot in Apples
What apple varieties are most susceptible?
McIntosh Cortland, Empire and Northern Spy varieties tend to be the most susceptible. However, other varieties can also be affected.
How is black rot different from apple scab?
Scab mainly affects leaves and fruit surfaces, while black rot penetrates deeper and causes rotting fruit. Scab has an olive-green velvety appearance, while black rot shows distinct concentric rings.
Can black rot spread to other trees besides apples?
Yes, it can occasionally spread to nearby pear or quince trees. It mainly infects already damaged or dead tissue on other tree species.
Does black rot also affect apple tree branches?
Yes, the fungus can infect branches and twigs, causing cankers (sunken lesions) to form. These serve as sources of spores for new infections.
Can black rot be controlled without fungicides?
In home orchards, diligent sanitation practices like pruning out diseased wood and removing mummified fruit can provide adequate control in some cases without fungicides. However, fungicides provide an added layer of protection in wet seasons conducive to this disease.
Controlling black rot takes persistence and vigilance, but this troublesome apple disease can be successfully managed. Follow the treatment guidelines outlined here to keep your apple trees healthy and productive for years to come. With prompt action at the first signs of infection, you can limit the damage caused by this harmful fungus.
What is Black Rot?
Black rot is a disease of apples that infects fruit, leaves, and bark caused by the fungus Botryosphaeria obtusa. It can also jump to healthy tissue on pear or quince trees but is typically a secondary fungus of weak or dead tissues in other plants. Begin checking your apple trees for signs of infection about a week after the petals fall from your apple blossoms. Early symptoms are often limited to leaf symptoms such as purple spots on upper leaf surfaces. As these spots age, the margins remain purple, but the centers dry out and turn yellow to brown. Overtime, the spots expand, and heavily infected leaves drop from the tree. Infected branches or limbs will show characteristic red-brown sunken areas that expand each year. Fruit infection is the most destructive form of this pathogen and begins with infected flowers before fruits expand. When fruits are tiny and green, youll notice red flecks or purplish pimples that enlarge as the fruit does. Mature fruit lesions take on a bulls-eye appearance, with bands of brown and black areas expanding outward from a central point in each lesion. Commonly, black rot disease causes blossom end rot or mummification of the fruits on the tree.
Apple Black Rot Control
Treating black rot on apple trees starts with sanitation. Since fungal spores overwinter on fallen leaves, mummified fruits, dead bark, and cankers, its important to keep all the fallen debris and dead fruit cleaned up and away from the tree. During the winter, check for red cankers and remove them by cutting them out or pruning away the affected limbs at least 6 inches (15 cm.) beyond the wound. Destroy all infected tissue immediately and keep a watchful eye out for new signs of infection. Once black rot disease is under control in your tree and youre again harvesting healthy fruits, make sure to remove any injured or insect-invaded fruits to avoid re-infection. Although general-purpose fungicides, like copper-based sprays and lime sulfur, can be used to control black rot, nothing will improve apple black rot like removing all sources of spores.