Chrysanthemum White Rust

What is Chrysanthemum White Rust?

Chrysanthemum White Rust (CWR) is a potentially devastating fungal disease that affects members of the Asteraceae family, with chrysanthemums being the primary host.

Regions Impacted

Originating in eastern Asia, chrysanthemum white rust has spread to regions like the Far East, Europe, Africa, Australia, Central America, and South America. Although outbreaks have occurred in Canada and the United States, swift eradication measures have been successful in controlling the pest.

What are the Symptoms?

• Yellow Spots: Initial symptoms of Chrysanthemum White Rust often appear as small, yellowish spots on the upper surface of the leaves. These spots can be easily overlooked or mistaken for other issues, which makes early detection challenging.
• White to Pinkish Pustules: As the disease progresses, the undersides of the leaves display the most distinctive sign of Chrysanthemum White Rust: the development of white to pinkish pustules. These raised growths are where the fungus produces its spores.
• White Spore Release: The pustules rupture to release white to off-white spores, which gives the disease its name. This sporulation can cause the underside of the leaf to appear powdery or dusty.
• Leaf Distortion: Leaves affected by the rust may become distorted, especially if the infection is severe. This can lead to curling, twisting, or other deformities in leaf shape.
• Necrosis: Surrounding the pustules, there might be areas of dead tissue, which can turn brown to black. Over time, if the disease continues unchecked, the entire leaf might die.
• Pustules on Stems and Flowers: In severe infections, the white pustules can also appear on stems and even on the flowers of the chrysanthemum, although this is less common than leaf infection.
• Overall Plant Decline: If left untreated, Chrysanthemum White Rust can cause a general decline in the health and vitality of the plant, impacting its growth, flowering potential, and overall appearance.

Recognizing these symptoms early and taking swift action is crucial in managing Chrysanthemum White Rust, as the disease can spread quickly under favorable conditions and can cause significant damage to chrysanthemum crops.

What Causes this Rust?

Chrysanthemum White Rust is caused by the fungus Puccinia horiana. The fungus produces spores that can be spread by wind, water, or by contaminated tools, clothing, and plant materials.

How to Control and Prevent Chrysanthemum White Rust?

• Sanitation: Always start with clean planting material. Ensure that the plants you purchase or propagate are free from the disease.
• Quarantine: If you suspect a plant is infected, immediately isolate it from other plants to prevent the spread.
• Regular Inspection: Regularly inspect chrysanthemums for signs of the disease. Catching it early can prevent a more severe outbreak.
• Environmental Control: Reduce humidity around plants. The fungus thrives in moist conditions. Improve air circulation and avoid overhead watering.
• Cultural Practices: Plant chrysanthemums in well-draining soil and space them adequately to prevent overcrowding.
• Resistant Varieties: Some chrysanthemum varieties may show resistance or reduced susceptibility to CWR. Opting for these can reduce the risk of infection.
  • Painted Daisy (Chrysanthemum carinatum)
  • Crown Daisy (Chrysanthemum coronarium)
  • Pyrethrum (Tanacetum coccineum = Chrysanthemum coccineum)
  • Marguerite Daisy (Argyranthemum frutescens)
  • Ox-eye Daisy (Leucanthemum vulgare)
  • Shasta Daisy (Leucanthemum X superbum = Chrysanthemum maximum)
  • Corn marigold (Chrysanthemum segetum)
• Destruction of Infected Material: If a plant is heavily infected, it might be best to destroy it to prevent the spread of the disease. Always dispose of diseased plant material away from the garden, preferably by burning.
• Fungicides: Protective fungicides can be applied to prevent infection, especially during wet seasons or if the disease has been known to be present in the area.

In conclusion, Chrysanthemum White Rust is a significant threat to chrysanthemums and can cause considerable damage if not detected and treated promptly. Prevention through cultural practices and regular inspections, combined with prompt action at the first sign of infection, can help manage and control this disease.