This blog offers comprehensive details on the impact of diseases on citrus fruits and the simple methods farmers can use to detect and stop them.

Citrus fruits are now cultivated in more than 140 nations where suitable temperatures and water availability exist. The widespread use of the wide citrus varieties and the expansion of commercial planting have increased pests and diseases, leading to crop production losses and minor to severe damage to citrus fruits.

The primary reasons for the citrus decline are positively influenced by disease and insect incidence, climate extremes, poor soil fertility, low-quality planting materials, and poor orchard management.

This blog carries comprehensive information on the significant citrus diseases and the best ways to prevent them.

Significant diseases of citrus are:

1. Anthracnose
2. Citrus canker
3. Gummosis

Anthracnose

Anthracnose is a common disease in citrus fruits. It was initially observed in Sao Paulo state, China, and Brazil. When the fruit is grown in moist conditions, the prevalence of this disease can go up to 100%. Citrus anthracnose is distributed globally and can be found in Pakistan, Brazil, China, and India. The states with the highest disease rates in India are Tamil Nadu, Karnataka, and Andhra Pradesh, among others.

Symptoms

Leaf: 

• Common symptoms include a roughly round, flat region that is light tan in colour with a solid purple edge. At a later stage of infection, this area will reveal the fungus’s fruiting bodies (tiny dispersed black dots).
• Anthracnose colonization is more likely to occur on tissues that have been damaged by numerous environmental conditions (such as mesophyll collapse or severe spider mite infestations).

Fruit:

• Fruit that has been harmed by other factors, such as sunburn, chemical burn, bug damage, bruising, or prolonged storage periods, is typically the only fruit that develops anthracnose. The lesions are 1.5 mm or larger-diameter brown to black spots.
• The deterioration is usually solid and dry, but if it penetrates deeply enough, it might soften the fruit. The spore masses have a pink to salmon colour in humid conditions but a brown to black colour when kept in dry conditions. 
• Fruit exposed to ethylene develops flat lesions, silver in colour and leathery in texture. On degreened fruit, the exterior portion is primarily affected. Over time, the lesions will turn from brown to black, and soft rot will develop as a result.

Favourable circumstances

• Disease development in plants is caused by cool temperatures (20°C).
• Long-term high relative humidity >80% with mists

Management

• As the fungus thrives in dead branches, dead wood should be removed.
• Before the autumn rains, copper-based fungicide field sprays should be used.
• Fruit losses may be decreased by postharvest treatment with benzimidazole fungicides.

Citrus Canker

Citrus canker is the most lethal disease. The disease impacts all of the significant citrus fruit crops in that area. The disease causes enormous losses to citrus, and its severity varies depending on cultivars and the local climate. The disease is endemic in Southeast Asian nations, including India, Japan, and others. The disease was first found in India in the Punjab state.

Symptoms

• The disease first manifests as tiny, round, yellow spots soaked in water. These spots gradually get more extensive and turn dark, eruptive, and corky.
• These pustules have a recognizable yellow halo around them.
• On fruit, canker lesions do not have the same yellow halo seen on leaves. Fruit blemishes may combine to generate bigger cankers.
• Defoliation and die-back signs on the twig and stem may occur due to severe infections.

Favourable circumstances

The disease is more likely to emerge in the spring season. The primary means of short-distance dissemination within and between trees is wind-driven rain and water splashing. The risk of spreading disease can rise with irrigation.

Management

• Before the monsoon, prune out and burn all canker-infected twigs. 
• Choose seedlings free of canker for planting in the main field.
• Keep the leaf wetness time to a minimum by training and pruning to maintain optimum aeration.
• After the emergence of new growth, repeatedly spray a 50 to 100 ppm solution of streptocycline at intervals of 15 to 20 days.
• Completely cover the immature fruits and leaves.

Gummosis

Gumming disease of citrus is another name for this disease. It is a fungal disease. Long-term moist and rainy conditions might lead to soil or nursery plant infection. Common citrus fruits affected by this disease include mandarin, sweet orange, lemons, and others. Gummosis is one of the major diseases affecting the cultivation of citrus fruits.

Symptoms 

• Large water-soaked spots on the basal sections of the stem close to the ground are the first signs of disease.
• In such areas, bark dries up, contracts, cracks, and shears into vertical strips that run the length of the tree.
• Later, there is a massive exudation of gum from the trunk’s bark.
• Grapefruit exhibits relatively minimal gum development compared to sweet oranges, which exhibit a significant quantity.

Favourable circumstances for disease

The Phytophthora species that cause gummosis multiply in moist, cold environments. These conditions favour the prevalence of the disease.

Management

• Diseased bark should be removed, and a portion of the healthy strip should also be removed around the infection as a buffer.
• Preventive actions such as choosing a suitable site with sufficient drainage.
• The use of resistant rootstocks is effective in controlling the pest.
• Effective irrigation methods include using the ring method to prevent water contact with the tree trunk. Also, farmers should look for contactless irrigation methods like drip irrigation.

How can Fasal assist?

• The leading causes of disease infection in citrus fruits are harsh climatic conditions, high relative humidity, irregular watering, etc.
• Fasal is an AI-powered IoT device that has helped countless farmers achieve increased yields.
• The AI-based device is equipped with several sensors that monitor rain, soil moisture, soil temperature, wind direction, leaf wetness, and other macro- and microclimatic factors at the farm level. The hardware device’s data is processed based on agronomic models to create actionable alerts for farmers.
• The Fasal Disease and Pest Prevention System provide advisories on the best preventive sprays to minimize damage while warning farmers about the potential disease and pest outbreaks. 
• With the help of these warnings, farmers have reduced pesticide use by 15-30%, lowering the environmental impact. 
• The farmers can prevent disease/pest attacks on their crops using Fasal’s system well in advance of the occurrence of such an event.

Fasal technology satisfies farmers, knowing that their crops are in good hands.