Welcome to our comprehensive guide on common citrus tree diseases! If you’re a citrus enthusiast or a proud owner of these vibrant trees, it’s crucial to understand the potential threats they face. This blog explores disease symptoms, spread, control, prevention, and management.
Common Citrus Tree Diseases
Overview of Citrus Farming and Production
Because of its importance in agriculture, India is ranked as the world’s fifth-largest producer of citrus fruits. India is a prominent contributor to the global citrus industry alongside other countries, including Spain, the United States, Israel, Morocco, South Africa, Japan, Brazil, Turkey, and Cuba. North East India is pivotal in the history of various citrus species originating in Southeast Asia’s tropical and subtropical regions, including India and China. India’s vast citrus groves, covering 846,000 ha, yield a massive 7,464,000 metric tons annually.
Orange (mandarin or tantra), sweet orange (mosambi, malta, or study), and lime/lemon (known as ‘Pati lime’ or ‘Kagzi lime’) are all popular commercial citrus cultivars in India. The most important citrus-growing regions in India include the states of Maharashtra, Andhra Pradesh, Punjab, Karnataka, Uttarakhand, Bihar, Orissa, Assam, and Gujarat. Unfortunately, over 250 bug and mite species negatively impact plant growth in India’s citrus orchards, especially during the fresh flush period. Brazil, China, India, Mexico, and Spain are the top five countries producing citrus.
Most Common Citrus Tree Diseases
The world of citrus trees is not immune to diseases, and being aware of the most common ones is essential for citrus growers. Citrus Canker, caused by the bacterium Xanthomonas citri subsp. citri, results in raised corky lesions on fruits, leaves, and stems. Citrus Tristeza Virus leads to tree decline and reduced fruit quality. Phytophthora Foot Rot causes root decay, leading to wilting and death. Citrus Scab, caused by the fungus Elsinoë fawcettii, creates scaly lesions on fruits. Citrus Black Spot, caused by the fungus Guignardia citricarpa, causes dark, sunken spots on fruits.
Gummosis Diseases of Citrus Tree Control and Management
Gummosis is a citrus tree disease caused by pathogens like Phytophthora parasitica, P. palmivora, and P. citrophthora.
Symptoms and Disease Spread
Its symptoms include yellowing of leaves, bark cracking, and excessive gumming on the surface. The primary source of infection is infected planting material. Severe gumming leads to the decay of the bark, resulting in the tree drying out due to girdling. Sometimes, the tree may bloom heavily but die before the fruits mature, known as foot rot or collar rot. The pathogen responsible for gummosis exhibits aseptate, intercellular, and intracellular hyphae. The spread of the disease occurs through soil inhabitants and sporangia carried by rainwater, irrigation water, and wind.
Effective Management
- Selecting well-drained sites.
- Using resistant rootstocks.
- Preventing water contact with the trunk through ring irrigation.
- Scraping out diseased portions and disinfecting the cut surface.
- Painting the stem with a Bordeaux mixture.
- Utilizing fungicides like Ridomil MZ 72 and Aliette.
Scab/Verucosis Diseases of Citrus Tree Control and Management
Scab/Verucosis, caused by the pathogen Elsinoe Fawcett, exhibits distinct symptoms on citrus trees.
Symptoms and Disease Spread
In the early stages, small semi-translucent dots appear on the underside of the leaves, eventually developing into raised pustular elevations. The leaves can become distorted, wrinkled, stunted, and deformed as the disease progresses. On the fruit, corky projections form, which may break and result in scabs. The affected area shows a circular depression with a pink-to-red center on the opposite surface.
The pathogen’s ascostroma are simple, innate, and either intra or sub-epidermal. They are partially erumpent at maturity and range from small pulvinate to crustose structures. The asci are ovoid, and the ascospores are oblong to elliptical with 1-3 septa, appearing hyaline to yellowing. Conidia, produced in acervuli, are hyaline, oblong, and