Chrysanthemum white rust Chrysanthemum white rust Chrysanthemum white rust is a disease of plants caused by the fungus Puccinia horiana that infects species of the genus "Chrysanthemum". Chrysanthemum white rust was first identified in Japan, although it is now established throughout Asia, Europe, South America. It has been found in the United States, Australia, and New Zealand on several occasions, but early detection and eradication efforts have prevented the disease from becoming established in these countries. Plants infected by chrysanthemum white rust exhibit spots on the upper surfaces of leaves. These spots are initially pale-green to yellow in color and up to 5mm
Stem rust the end of the growing season black telia are produced. For this reason stem rust is also known as 'black rust'. The telia are firmly attached to the plant tissue. The site of infection is a visible symptom of the disease. Pycnia appear on barberry plants in the spring, usually in the upper leaf surfaces. They are often in small clusters and exude pycniospores in a sticky honeydew. Five to ten days later, cup-shaped structures filled with orange-yellow, powdery aeciospores break through the lower leaf surface. The aecial cups are yellow and sometimes elongate to extend up to 5 mm