New Emerging Disease: How to manage the problem of sudden withering and wilt of a litchi tree?

By: Merikheti
Published on: 18-Dec-2023

Litchi (litchi chinensis) is a tropical and subtropical fruit tree known for its juicy and aromatic fruits. Diseases in litchi are less. For successful cultivation of litchi, it is necessary to manage the insects that attack it. But for the last few years, Wilt Disease has been seen in litchi which is a vascular disease caused by fusarium oxysporum/solani fungi. This pathogen mainly attacks the root system, disrupts the transport of water and nutrients and makes the tree dry, yellow, and eventually causes death.


Symptoms of Wilt disease in litchi


Although this disease can affect litchi trees of any age, this wilt disease is usually seen more in the new trees of litchi under five years of age, in which the trees would wither away in less than a week. The first symptoms appear as yellow leaves, after that the leaves fall, gradually withering and drying, causing a complete death of the plant within 4-5 days. This fusarium is caused by oxysporum/solani fungus. This requires more research. There is still very few literature available on this disease. Wilt symptoms in litchi are similar to Wilt disease in common. Litchi's Wilt Disease (Wither) is caused by the soft -worn fungus Fusarium oxysporum/solani, which is a terrible threat to litchi orchards worldwide. To maintain litchi cultivation, it is very important to understand the disease, its life cycle and to know management strategies.


Identification and life cycle of fusarium oxysporum


Litchi withering causing agent Fusarium oxysporum/solani, belongs to a group of mild fungi which is known for its wide host border and firmness in the soil. The pathogen infects litchi trees through the roots, occupies the vascular system and causes obstruction of water-rich vessels. As a result, the plants begin to fade and eventually the tree dies. The life cycle of fusarium oxysporum/solani involves surviving as a chlamydospore resistant to the soil. These spores can persist for years, when a sensitive host faces the susceptible root system waiting to be infected, the fungus sprouts and enters the roots, and installs itself in vascular tissues. Then the fungus produces more spore, completes the cycle and maintains the disease.


Factors Contributing to Wilting of Litchi


Many factors contribute to the development and spread of wilting of litchi such as…


Soil Conditions: Fusarium oxysporum thrives in warm and moist soil conditions. Poor drainage and waterlogged soils create an ideal environment for the fungus to infect litchi trees.


Varying susceptibility: Some litchi varieties exhibit resistance to Fusarium oxysporum, others are highly susceptible. The choice of variety significantly affects the susceptibility of the garden to litchi wilt.


Temperature and humidity: Warm temperatures and high humidity favor the growth and spread of Fusarium oxysporum. These climatic conditions provide optimal conditions for pathogens to infect litchi trees.


How to Manage Litchi Wilt Disease?


Management of litchi wilt requires a holistic approach that combines preventive measures, cultural measures, chemical treatments, biological control, sanitation and ongoing research on resistant varieties. Let's take a deeper look at each of these components:


1. Preventive measures

Site Selection: It is important to select well-drained sites to reduce the risk of litchi wilting. Avoiding waterlogged areas helps create a less favorable environment for Fusarium oxysporum.


Selection of resistant varieties: Planting litchi varieties with inherent resistance to the pathogen is a proactive strategy. Ongoing research aims to identify and develop resistant varieties that can withstand Fusarium oxysporum.


2. Cultural (agricultural) measures

Irrigation Management: Proper irrigation practices are essential. It is important to maintain a balance between waterlogging and drought stress to create unfavorable conditions for Fusarium oxysporum. Drip irrigation systems can help deliver water directly to the root zone, reducing soil contact with the pathogen.


Pruning and thinning: Regular pruning of infected branches and thinning of the canopy promote air circulation, reducing moisture around the tree. This, in turn, reduces the chances of fungal spores germination and infection.


Distance between trees: It is very important to have adequate distance between litchi trees. The increased distance facilitates better air circulation, reduces humidity and limits the spread of Fusarium oxysporum.


3. Chemical treatment

Fungicide Application: Fungicides play an important role in the management of wilt of litchi. Fungicides containing active ingredients such as thiophanate-methyl and propiconazole have demonstrated efficacy against Fusarium oxysporum/solani. With preventive treatments implemented during the early stages of disease development, timing of application is important. Treat the soil (active root zone) with a solution of Hexaconazole or Propiconazole @ 2 ml per litre of water or a fungicide called Carbendazim or Roco M @ 2 grams per liter of water and thoroughly soak the soil around the tree. After ten days, thoroughly soak the soil around the tree again with the same solution.



Integrated disease management (IDM): Integrating fungicides with other disease management practices reduces the risk of resistance developing. The IDM approach considers the ecological context and aims for sustainable, long-term disease control.


4. Biological control

Beneficial Microorganisms: Some beneficial microorganisms such as various species of Trichoderma have shown promise in suppressing Fusarium oxysporum/solani. These biocontrol agents can be applied to the soil or used as foliar sprays, providing a natural and environmentally friendly means of disease management.


In litchi, apply Neem cake or castor cake @ 5-8 kg/tree along with recommended dose of fertilizer according to the age of the tree or apply Burmese compost @ 20-25 kg per tree. The use of biocontrol agents such as Trichoderma harzianum, Trichoderma viridi, Pseudomonas fluorescens, etc. has proven effective in the management of the disease. Mix 100-200 grams of commercial formulation of Trichoderma with 20 kg of well-rotted cow dung or compost and spread it per adult tree in the active root zone in a circular strip about 30-40 cm wide on the soil surface at a place where Provide water that is about two feet inside the outer limit of the tree canopy. Ensure adequate moisture in the soil by spraying water or do light irrigation


Microbial consortia: Research is ongoing to develop microbial consortia that utilize the synergistic effects of multiple beneficial microorganisms. These consortia offer advanced disease suppression while reducing environmental impact.


5. Cleanliness

Debris Removal: It is important to promptly remove and destroy infected plant debris to eliminate potential sources of inoculum. Fallen leaves, cut branches and other plant material should be disposed of properly to prevent the persistence of Fusarium oxysporum in the garden.


Tool Disinfection: Regular disinfection of pruning tools and equipment helps prevent the inadvertent spread of fungus between trees. Hygiene is essential to reduce the risk of disease transmission during garden maintenance.


6. Research on resistant varieties

Breeding Programme: Continuous efforts in breeding programs are aimed at developing litchi varieties with inherent resistance to Fusarium oxysporum. Identifying and promoting resistant varieties is a sustainable long-term solution to litchi wilt.


Genetic Engineering: Advances in genetic engineering can accelerate the development of resistant varieties. By introducing genes that confer resistance to Fusarium oxysporum, researchers aim to increase litchi's ability to withstand the pathogen.


7. Precision Agriculture Technology

Remote sensing: Precision agriculture technologies, including remote sensing, enable growers to monitor orchard health from a distance. Drones equipped with sensors can detect early signs of disease, allowing targeted intervention and timely disease management.


Data Analytics: Analysis of data collected through precision agriculture technologies provides valuable insights into disease dynamics. This information guides growers in optimizing management practices and improving overall orchard health.


Summary


Litchi Wilt (Wither) management requires multidimensional and integrated approaches. From preventive measures and cultural measures to chemical remedies, biological control, hygiene and ongoing research on resistant varieties, each component plays an important role in reducing the impact of fusarium oxysporum. It is necessary to ensure the livelihood of producers facing a holistic strategy, maintaining litchi orchards, and through the challenges of lychee withering.