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10 Diseases of Avocado Trees

Did you know that Kenya is one of the top producers of avocados in the world? In fact, according to the Kenya National Bureau of Statistics, avocado exports brought in over Ksh 14 billion (USD 140 million) in revenue in 2019 alone. However, diseases of avocado hamper the industry’s growth as local farmers need to meet stringent export requirements. 

The main export Avocado is Hass. You can know more about Hass Avocado farming in Kenya by reading the prepared guide. The guide will help you enter the export market and increase yields by at least 30%.

In Kenya, various factors, such as climate and soil type, contribute to the prevalence of avocado diseases. According to a study published in the African Journal of Horticultural Science, up to 80% of avocado trees in Kenya are affected by diseases, with fungal and bacterial diseases being the most prevalent. 

This article will explore ten of the most common avocado diseases in Kenya and their management strategies to help farmers protect their crops and livelihoods.

10 Diseases of Avocados Trees in Kenya

The first disease of avocado trees that we will discuss is Anthracnose. Anthracnose is a fungal disease affecting avocado tree leaves, stems, and fruits. The symptoms of anthracnose vary depending on the affected plant part.

In avocado leaves, anthracnose appears as small, dark, water-soaked spots that eventually enlarge and turn brown or black. The spots can coalesce, causing the leaves to yellow and drop prematurely.

In avocado fruit, anthracnose causes small, circular, sunken lesions that are dark brown or black in color. The lesions can expand, covering large areas of the fruit, and can also cause the fruit to rot. In severe cases, anthracnose can cause defoliation, stunted growth, and reduced fruit yield. 

It is important to note that anthracnose symptoms can be mistaken for those of other diseases, such as scab and bacterial canker. Therefore, it is essential to seek the advice of a plant pathologist or agronomist for proper diagnosis and management.

In avocado leaves, anthracnose appears as small, dark, water-soaked spots that eventually enlarge and turn brown or black. The spots can coalesce, causing the leaves to yellow and drop prematurely.

In avocado fruits, anthracnose causes small, circular, sunken lesions that are dark brown or black in color. The lesions can expand, covering large areas of the fruit, and can also cause the fruit to rot.

In severe cases, anthracnose can cause defoliation, stunted growth, and reduced fruit yield. It is important to note that anthracnose symptoms can be mistaken for those of other diseases, such as scab and bacterial canker. Therefore, it is essential to seek the advice of a plant pathologist or agronomist for proper diagnosis and management. Other diseases of avocado trees are:

2. Phytophthora Root Rot

In young avocado trees, the first symptom of Phytophthora root rot is wilting of the leaves, which is often followed by a rapid decline in plant growth. The roots of affected trees appear brown or black and are soft and spongy to the touch.

In mature avocado trees, the symptoms of Phytophthora root rot may be less noticeable. However, affected trees may exhibit a reduced growth rate, thinning canopy, and declining fruit yield and quality. The bark of the trunk may also show signs of sunken cankers.

In avocado fruit, Phytophthora root rot causes the fruit to rot from the peduncle (stem) end, developing a brown, slimy mass. The fruit may also develop a sour smell and become soft to the touch.

It is essential to note that the symptoms of Phytophthora root rot can be similar to those of other root diseases, such as Armillaria root rot. Therefore, proper diagnosis is crucial for effective management. The disease can be controlled in three main ways:

  • Preventing waterlogging
  • Using disease-resistant varieties
  • Using a suitable fungicide with a combination of cultural practices 

3. Scab Disease

Scab disease in avocado trees and fruits is caused by a fungus called Sphaceloma perseae. The symptoms of this disease can vary depending on the severity of the infection, but some common symptoms are:

  • Lesions on leaves: The first symptoms of scab disease usually appear on the leaves. Small, circular, or irregularly shaped lesions appear on the upper surface of the leaves. These lesions are brown or black and may have a raised edge.
  • Lesions on fruits: As the disease progresses, lesions may also appear on the fruit. These lesions are similar to those on the leaves and can cause the fruit to become disfigured.
  • Cracking of the fruit: In severe cases, the lesions on the fruit can cause the fruit to crack or split open.
  • Premature fruit drop: Infected fruits may drop prematurely from the tree.
  • Defoliation: Severe infections can cause the leaves to turn yellow and fall off the tree.
  • Reduced yield: Scab disease can reduce the yield of the avocado tree, as infected fruits may be unsuitable for sale or consumption.

To control scab disease, follow the following guidelines:

  • Use disease-free planting materials: Ensure the planting materials are free from gumming disease infection to avoid introducing the disease into the field.
  • Sanitation practices: Remove and destroy all infected plant debris from the field, as it can be a source of inoculum for the disease.
  • Use of resistant varieties: Plant-resistant varieties are less susceptible to gumming disease. These varieties have genetic traits that can help reduce the severity of the disease.
  • Insect control measures: Control the insect vectors that spread the bacteria that cause gumming disease, such as leafhoppers and mealybugs. This can be achieved through the use of insecticides or biological control agents.
  • Cultural practices: Adopt good agricultural practices, such as proper drainage, irrigation, and fertilizer management, which can help reduce the severity of the gumming disease.

4. Avocado sunblotch viroid

This disease is transmitted through infected plant materials such as cuttings, seedlings, or contaminated pruning tools.

The disease affects the avocado tree’s leaves, roots, and fruits. It causes yellowing and blistering of the leaves, which can lead to defoliation, stunted growth, and reduced yields. The infected tree’s fruits are also affected, leading to poor quality and reduced market value.

In addition to affecting the tree’s aerial parts, ASBVd can also infect the avocado tree’s roots. The disease can cause reduced root growth and development, leading to poor nutrient and water uptake by the tree. This can lead to further stunting and decline of the tree.

In severe cases, ASBVd can cause the death of the avocado tree. The disease has no cure, and infected trees should be removed and destroyed to prevent the further spread of the disease.

Effective management of ASBVd involves using disease-free planting materials, regular crop scouting and monitoring, and strict sanitation practices. The use of disease-resistant avocado varieties can also help reduce the impact of the disease on avocado production.

5. Bacterial Canker

Bacterial canker is a common disease that affects avocado trees and is caused by the bacterium Pseudomonas syringae. The bacterium infects the tree through wounds on the bark, usually caused by pruning, hail damage, or insect feeding. Once inside the tree, the bacterium multiplies and causes cankers, or swollen areas on the bark.

The cankers ooze bacterial exudates, which may dry up and form a crust around the canker. The exudate can also spread the bacterium to other parts of the tree or to other trees in the orchard. As the disease progresses, the cankers enlarge and cause dieback of the affected branches, leading to reduced fruit yield and tree decline.

Bacterial canker also affects the avocado fruit, causing small, water-soaked lesions that eventually turn brown and dry up. The lesions can coalesce and form larger areas of rot on the fruit, making it unmarketable. The disease can also cause premature fruit drop, leading to reduced fruit yield.

Management of bacterial canker involves cultural practices such as proper irrigation, fertilization, and pruning to minimize the risk of tree damage and entry points for the bacterium. Infected plant material should be removed and destroyed to prevent further spread of the disease. Chemical control using bactericides can also be effective in managing the disease, but it is important to use bactericides that are effective against the specific strain of the bacterium causing the disease.

6. Stem End Rot Disease

Stem-end rot is a common disease that affects avocado fruit and is caused by the fungus Colletotrichum gloeosporioides. The disease causes brown, dry rot on the stem end of the fruit, which can spread to the surrounding tissue and cause the fruit to become soft and unmarketable. Stem-end rot can also cause premature fruit drop, leading to reduced fruit yield.

Stem-end rot typically occurs during the fruit maturation and ripening stages, but can also occur in fruit that has been stored for a long time. The disease enters the fruit through wounds or cracks on the skin, usually caused by insect feeding or sunburn.

Stem-end rot can also affect the tree, causing cankers on the branches and trunk, and leading to dieback and reduced fruit yield. However, the impact of the disease on the tree is generally less severe than on the fruit.

Management of stem-end rot in avocado trees involves a combination of cultural practices and chemical control methods.

Cultural practices include:

  • Proper irrigation: Maintaining proper soil moisture levels can prevent water stress, which can make the tree more susceptible to stem-end rot.
  • Proper fertilization: Providing the tree with adequate nutrients can help it grow strong and healthy, and better resist disease.
  • Regular pruning: Pruning can help improve air circulation within the canopy, reducing humidity levels and the risk of fruit infection.
  • Harvesting: Careful harvesting practices can minimize the risk of fruit damage and infection.

Chemical control methods include

  • Fungicides: Fungicides can be used to control the disease, but it is important to use fungicides that are effective against the specific strain of the fungus causing the disease. Fungicides should be applied according to label instructions, and timing is critical to ensure that the disease is effectively managed
  • Sanitation: Removing and destroying infected plant material can help prevent the spread of the disease.
  • Post-harvest treatment: Treating the fruit with fungicides after harvest can prevent the disease from spreading during storage and transportation.

7. Powdery Mildew

Powdery mildew is a fungal disease that can affect avocado trees and fruits. The fungus that causes powdery mildew, Podosphaera xanthii, infects avocado tree leaves, stems, and fruit.

When avocado trees are infected with powdery mildew, the disease can cause a range of symptoms, including white or greyish powdery patches on the tree’s leaves, stems, and fruit. The powdery mildew can also cause the leaves to curl, twist, and turn yellow or brown. In severe cases, the leaves can fall off the tree, reducing the tree’s ability to photosynthesize and produce fruit.

In addition to affecting the leaves and stems of avocado trees, powdery mildew can also affect the fruit of the tree. Infected fruit may develop a powdery white or greyish coating, which can cause the fruit to become discoloured and deformed. The fruit may become cracked or distorted in severe cases, making it unmarketable.

Powdery mildew can also affect the overall health of the avocado tree, reducing its growth rate, yield, and fruit quality. Severe infections can lead to defoliation and weaken the tree, making it more susceptible to other diseases and pests.

To control powdery mildew in avocado trees, it is important to maintain good orchard hygiene by removing infected plant debris and pruning affected branches. Fungicides may also be used to control powdery mildew, but following the manufacturer’s instructions and using them responsibly to avoid resistance development is important.

8. Black Streak Avocado Disease

Black streak disease in avocado trees is caused by a virus called Avocado sunblotch viroid (ASBVd), and it can affect both the tree and its fruit. Here are some ways black streak disease can affect avocado trees and fruits:

Reduced yield: Black streak disease can lead to a reduction in fruit yield as infected trees produce fewer fruits.

  • Stunted growth: The disease can cause the tree to become stunted and grow slower than healthy trees.
  • Leaf discoloration: The leaves of infected trees may become yellow, pale, or bronze.
  • Fruit discoloration: Infected fruits may have black streaks, necrotic areas, or ring spots that reduce the marketability of the fruit.
  • Poor quality fruit: The fruit may have a dry, mealy texture and a bitter taste, making it unsuitable for sale or consumption.
  • Tree death: In severe cases, black streak disease can cause the death of the avocado tree.

It is important to note that black streak disease can be transmitted through grafting, contaminated pruning tools, and seed propagation, so it is essential to practice proper sanitation measures to prevent the spread of the disease

 

This Post Has 2 Comments

  1. Karen

    What is the gel like substance in the fruit of the avacado tree?

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