Mango and Citrus diseases | Diseases of Field & Horticultural Crops & Their Management-II

Unit-III

Syllabus
Fruits crops:
Mango: anthracnose, malformation, bacterial blight, and powdery mildew;
Citrus: canker and gummosis;
Grapevine: downy mildew, Powdery mildew;
Apple: scab, powdery mildew, and crown gall;
Peach: leaf curl.

Part - A
Mango and citrus diseases and their management

Mango

Anthracnose

Anthracnose is a common fungal disease that affects mango crops. The disease is caused by the fungus Colletotrichum gloeosporioides. The symptoms of anthracnose in mango crops include the appearance of dark, sunken lesions on the fruit skin. These lesions may be small at first but can grow larger and merge with other lesions, causing the fruit to rot.

Anthracnose can also affect other parts of the mango tree, including the leaves, stems, and flowers. On the leaves, the disease causes the appearance of brown spots with yellow halos, while on the stems and flowers, it causes cankers and dieback.

Anthracnose is spread through the air or by contact with infected plant material. The disease is more common in warm, humid conditions, which create ideal conditions for the growth and spread of the fungus. To manage anthracnose in mango crops, several practices can be employed.

Cultural Control: Cultural control methods include pruning infected branches, removing infected fruit from the tree, and burying infected plant material to prevent the spread of the disease.

Chemical Control: Fungicides can also be used to manage anthracnose in mango crops. Fungicides containing azoxystrobin, trifloxystrobin, and pyraclostrobin have been found to be effective against anthracnose in mango crops.

Biological Control: Biological control methods involve the use of microorganisms, such as Trichoderma spp. and Bacillus subtilis, to suppress the growth of the anthracnose fungus.

Integrated Disease Management (IDM): A combination of the above control methods can be used as an integrated disease management strategy to manage anthracnose in mango crops.

It is important to note that prevention is key when it comes to managing anthracnose in mango crops. Farmers should practice good orchard hygiene by removing infected plant material, using disease-free planting material, and avoiding overhead irrigation, which can create ideal conditions for the growth and spread of anthracnose fungus.

Malformation

Mango malformation is a physiological disorder that affects mango trees. The exact cause of the disorder is not fully understood, but it is believed to be caused by a combination of factors, including genetics, environmental conditions, and viral infections.

The symptoms of mango malformation include the appearance of swollen, distorted, and stunted vegetative shoots, as well as the development of abnormally shaped inflorescences (flowering structures) and fruits. The leaves on affected shoots may also be smaller, thicker, and darker in colour than normal leaves.

Mango malformation is more common in younger trees and is most severe during the first few years of growth. The disorder can result in reduced fruit production and poor fruit quality, as malformed fruits are often small, deformed, and of low quality.

To manage mango malformation, several practices can be employed:

1. Cultural Control: Cultural control methods include pruning affected shoots and branches, and removing and destroying malformed fruits. These practices help to reduce the spread of the disorder within the orchard.
2. Chemical Control: Fungicides and bactericides can be applied to the trees during the dormant season to control any secondary infections that may occur as a result of the malformation.
3. Nutritional Management: Nutritional management can also help to reduce the severity of mango malformation. Adequate nutrition, particularly the use of balanced fertilizers, can help to promote healthy growth and development of the trees, which in turn can help to reduce the severity of the disorder.
4. Virus Management: The use of virus-free planting material and the removal of infected trees from the orchard can help to prevent the spread of the viral infections associated with mango malformation.

It is important to note that prevention is key when it comes to managing mango malformation. Farmers should select planting material from reliable sources and ensure that the orchard is well-maintained with proper irrigation, fertilization, and pruning practices. Regular monitoring of the orchard for any signs of malformation and prompt action to control the disorder can help to reduce the impact of mango malformation on crop yields and fruit quality.

Bacterial Blight:

Bacterial blight is a serious disease of mango crops caused by the bacterium Xanthomonas campestris. The disease is more prevalent in areas with high humidity and frequent rainfall. The symptoms of bacterial blight in mango crops include the appearance of small, water-soaked lesions on the leaves and fruit. These lesions may become necrotic and sunken as the disease progresses, and can cause the fruit to rot and drop prematurely from the tree.

To manage bacterial blight in mango crops, several practices can be employed:

• Cultural Control: Cultural control methods include pruning infected branches, removing infected fruit from the tree, and burying infected plant material to prevent the spread of the disease.
• Chemical Control: Copper-based fungicides can be used to control bacterial blight in mango crops. However, it is important to note that excessive use of copper-based fungicides can lead to the development of copper-resistant strains of the bacterium, and can also have negative impacts on soil health and beneficial microorganisms.
• Biological Control: Biological control methods involving the use of beneficial microorganisms such as Bacillus subtilis and Pseudomonas fluorescens can also help to suppress the growth and spread of the bacterial blight pathogen.
• Integrated Disease Management (IDM): A combination of the above control methods can be used as an integrated disease management strategy to manage bacterial blight in mango crops.

Powdery Mildew:

Powdery mildew is a fungal disease that affects mango crops caused by the fungus Oidium mangiferae. The disease is more prevalent in areas with high humidity and temperatures ranging from 20-30°C. The symptoms of powdery mildew in mango crops include the appearance of a white or grey powdery coating on the leaves, stems, and fruits of the tree. The affected leaves may also curl, distort, and turn yellow, and the fruit may be stunted and of low quality.

To manage powdery mildew in mango crops, several practices can be employed:

• Cultural Control: Cultural control methods include removing infected plant material, providing good air circulation around the tree, and avoiding overhead irrigation.
• Chemical Control: Fungicides containing sulfur, myclobutanil, and propiconazole can be used to control powdery mildew in mango crops.
• Biological Control: Biological control methods involving the use of beneficial microorganisms such as Trichoderma harzianum can also help to suppress the growth and spread of the powdery mildew fungus.
• Integrated Disease Management (IDM): A combination of the above control methods can be used as an integrated disease management strategy to manage powdery mildew in mango crops.

It is important to note that prevention is key when it comes to managing both bacterial blight and powdery mildew in mango crops. Farmers should practice good orchard hygiene by removing infected plant material, using disease-free planting material, and avoiding overhead irrigation, which can create ideal conditions for the growth and spread of these diseases.

Citrus

1. Citrus Canker:

Citrus canker is a highly contagious bacterial disease that affects citrus crops, causing lesions on the leaves, stems, and fruit of the tree. The disease is caused by the bacterium Xanthomonas axonopodis. The symptoms of citrus canker in citrus crops include the appearance of small, raised, water-soaked lesions on the leaves, stems, and fruit of the tree. These lesions can become surrounded by a yellow halo and may exude a sticky, watery substance. Over time, the lesions can enlarge and cause leaf drop, twig dieback, and fruit rot, leading to significant yield losses.

To manage citrus canker in citrus crops, several practices can be employed:

• Cultural Control: Cultural control methods include pruning infected branches, removing infected fruit from the tree, and burying infected plant material to prevent the spread of the disease.
• Chemical Control: Copper-based fungicides can be used to control citrus canker in citrus crops. However, it is important to note that excessive use of copper-based fungicides can lead to the development of copper-resistant strains of the bacterium, and can also have negative impacts on soil health and beneficial microorganisms.
• Biological Control: Biological control methods involving the use of beneficial microorganisms such as Bacillus subtilis and Pseudomonas fluorescens can also help to suppress the growth and spread of the citrus canker pathogen.
• Integrated Disease Management (IDM): A combination of the above control methods can be used as an integrated disease management strategy to manage citrus canker in citrus crops.

1. Gummosis:

Gummosis is a fungal disease that affects citrus crops caused by several species of the fungus Phytophthora. The disease is more prevalent in areas with high humidity and poorly drained soils. The symptoms of gummosis in citrus crops include the appearance of a dark, sunken lesion on the trunk of the tree, which exudes a gummy substance. Over time, the lesion can enlarge and cause dieback of the tree, leading to significant yield losses.

To manage gummosis in citrus crops, several practices can be employed:

• Cultural Control: Cultural control methods include improving soil drainage, avoiding overwatering, and providing good air circulation around the tree.
• Chemical Control: Fungicides containing copper, fosetyl-aluminum, and metalaxyl can be used to control gummosis in citrus crops.
• Biological Control: Biological control methods involving the use of beneficial microorganisms such as Trichoderma harzianum can also help to suppress the growth and spread of the gummosis fungus.
• Integrated Disease Management (IDM): A combination of the above control methods can be used as an integrated disease management strategy to manage gummosis in citrus crops.

It is important to note that prevention is key when it comes to managing both citrus canker and gummosis in citrus crops. Farmers should practice good orchard hygiene by removing infected plant material, using disease-free planting material, and avoiding overwatering, which can create ideal conditions for the growth and spread of these diseases.