Albugo occidentalis Albugo occidentalis Albugo occidentalis, the causal agent of Spinach White Rust, is an oomycete plant pathogen, although some discussions still treat it as a fungal organism. "Albugo occidentalis" is one of the most important spinach diseases in North America, found throughout the United States east of the rocky mountains. The economically important host of "Albugo occidentalis" is spinach (Spinacia oleracea); although the oomycete has also been reported to affect plants of the genus Chenopodium, the genus including the crop plant quinoa. This pathogen causes white rust or white blister of spinach. It is unrelated to the basidiomycete rusts biologically, but
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