What Is Canna Rust? A Detailed Explanation of This Common Disease
Canna
Canna rust is a disease with an extremely high incidence rate that mostly occurs in southern regions. It is mainly caused by a pathogenic fungus called Puccinia. Affected plants develop dry, withered leaves accompanied by dark brown spots, and also produce some cracked black dots. So what should be done when canna is infected with rust?
I. Symptoms
In the early stage of infection on canna leaves, small yellow water-soaked round spots appear on both the upper and lower surfaces, especially noticeable on the underside. Later, the spots gradually enlarge and develop blister-like protrusions. The lesions are orange-yellow to brown, 2-6 mm in diameter. On some varieties, a yellow-green halo ring appears at the edges. The blister-like protrusions on the lesions crack open and release orange-yellow powdery material, which is the uredinia and urediniospores of the pathogen. In winter, dark brown powdery material, namely telia and teliospores, appears on the lesions. Severely affected leaves are covered with numerous lesions that may merge into irregular large patches, causing localized necrosis of the leaves.
II. Pathogen
Canna rust (Puccinia thaliae) is caused by infection from a fungus in the Basidiomycota, Teliomycetes, Uredinales, Pucciniaceae, Puccinia genus. Urediniospores are yellow-white to orange-yellow, long ovate to elliptical, thick-walled, spiny, borne on short pedicels, measuring 20-25 × 16-22 micrometers; teliospores are long elliptical to club-shaped, with rounded or slightly flattened apex, narrower base, two-celled with slight constriction at the septum, pale yellow to yellow, measuring 35-60 × 13-18 micrometers.
III. Occurrence Patterns
Canna rust begins to occur in Guangzhou from March to April. Except for mild occurrence during hot summers and cold, dry weather in winter and spring, the disease is severe in other cool climates. The pathogen spreads urediniospores to healthy leaves through wind and water splashing; the spores germinate, invade, and cause repeated damage. Sometimes many grayish-dark brown spots appear on diseased leaves, with small black dots forming on them, while the yellow rust powder gradually decreases. This is the hyperparasite of the rust fungus (Darluca filum). This fungus and the rust fungus cause damage together, often worsening the condition and causing lesions to expand rapidly, with leaves curling and wilting.
IV. Control Methods
1. Strictly prohibit the introduction or export of infected propagation materials. In affected areas, diseased leaves should be pruned and seedlings disinfected before planting.
2. In winter, clear diseased leaves and diseased plant debris from the garden and burn them in a centralized manner.
3. During disease-prone seasons, spray with Bijunsha at 1000-1500 times dilution, 65% zineb at 400 times dilution, or 20% triadimefon emulsifiable concentrate at 2000-3000 times dilution, once every 7-10 days, alternating the products to prevent the disease. During severe outbreaks, spray with Penkejun at 2000-3000 times dilution, or use Amistar for control.
Canna Rust
Canna rust is a common disease in cities in southern China, with a very high incidence rate. In the early stage of infection, small yellow water-soaked round spots appear on both sides of diseased leaves, especially on the underside. Later, the small round spots enlarge and develop orange-yellow to brown blister-like protrusions with yellow-green halos at the edges, 2-6 mm in diameter. The epidermis of the blister-like protrusions ruptures, releasing orange-yellow powdery material (the uredinia of the pathogen). After autumn, brown powdery material (telia) appears on the lesions. Severely affected leaf surfaces are covered with lesions that may merge into irregular large necrotic areas. Diseased leaves turn yellow and eventually become brown and withered.
Pathogen and occurrence patterns: The pathogen is a species of Puccinia fungus. This fungus is often parasitized by a rust hyperparasite, causing dense dark brown spots to appear on existing lesions and producing some cracked black dot-like particles. The combination of these two types of damage worsens the condition, causing leaves to curl and wilt. In the Guangzhou area, the disease generally begins to occur in April. Except when the weather is hot and dry and the disease is mild, the disease remains severe from October through December when the climate is cool.
Control methods:
1. Strengthen garden sanitation management. In winter, as part of garden cleanup, promptly remove diseased leaves to reduce infection and spread. Thoroughly clear and burn diseased plant residues. During the disease period, promptly remove diseased leaves to reduce infection and spread.
2. Chemical control: In the early stage of disease, spray with 0.2-0.3 degrees Baume lime sulfur mixture or 20% carboxin emulsifiable concentrate at 400 times dilution, once every 10-15 days, to reduce the severity of damage. Spray with 65% zineb at 400 times dilution or 20% triadimefon emulsifiable concentrate at 2000-3000 times dilution, once every 7-10 days, alternating the products to reduce the condition.
3. Strictly prohibit the introduction or export of infected propagation materials. In affected areas, diseased leaves should be pruned and seedlings disinfected before planting.
How to Control Canna Rust
Canna rust is a common disease in cities in southern China, with a very high incidence rate. The leaves of affected plants gradually turn brown and wither. The root cause is a species of Puccinia fungus, which is often parasitized by a rust hyperparasite, causing dense dark brown spots to appear on existing lesions and producing some cracked black dot-like particles. The combination of these two types of damage worsens the condition, causing leaves to curl and wilt.
I. SymptomsIn the early stage of infection on canna leaves, small yellow water-soaked round spots appear on both the upper and lower surfaces, especially noticeable on the underside. Later, the spots gradually enlarge and develop blister-like protrusions. The lesions are orange-yellow to brown, 2-6 mm in diameter. On some varieties, a yellow-green halo ring appears at the edges. The blister-like protrusions on the lesions crack open and release orange-yellow powdery material, which is the uredinia and urediniospores of the pathogen. In winter, dark brown powdery material, namely telia and teliospores, appears on the lesions. Severely affected leaves are covered with numerous lesions that may merge into irregular large patches, causing localized necrosis of the leaves
II. PathogenCanna rust (Puccinia thaliae) is caused by infection from a fungus in the Basidiomycota, Teliomycetes, Uredinales, Pucciniaceae, Puccinia genus. Urediniospores are yellow-white to orange-yellow, long ovate to elliptical, thick-walled, spiny, borne on short pedicels, measuring 20-25×16-22 micrometers; teliospores are long elliptical to club-shaped, with rounded or slightly flattened apex, narrower base, two-celled with slight constriction at the septum, pale yellow to yellow, measuring 35-60×13-18 micrometers
III. Occurrence PatternsCanna rust begins to occur in Guangzhou from March to April. Except for mild occurrence during hot summers and cold, dry weather in winter and spring, the disease is severe in other cool climates. The pathogen spreads urediniospores to healthy leaves through wind and water splashing; the spores germinate, invade, and cause repeated damage. Sometimes many grayish-dark brown spots appear on diseased leaves, with small black dots forming on them, while the yellow rust powder gradually decreases. This is the hyperparasite of the rust fungus (Darluca filum). This fungus and the rust fungus cause damage together, often worsening the condition and causing lesions to expand rapidly, with leaves curling and wilting.
IV. Control Methods
(1) Strictly prohibit the introduction or export of infected propagation materials. In affected areas, diseased leaves should be pruned and seedlings disinfected before planting.
(2) In winter, clear diseased leaves and diseased plant debris from the garden and burn them in a centralized manner.
(3) During disease-prone seasons, spray with Bijunsha at 1000-1500 times dilution, 65% zineb at 400 times dilution, or 20% triadimefon emulsifiable concentrate at 2000-3000 times dilution, once every 7-10 days, alternating the products to prevent the disease. During severe outbreaks, spray with Penkejun at 2000-3000 times dilution, or use Amistar for control.