Local Blackberry Rust Found in Oregon

By Sen Speroff

This is how the Oregon Department of Agriculture describes the impact of Himalayan blackberry (Rubus fruiticosus aggregate):

“Himalayan blackberry is the most widespread and economically disruptive of all the noxious weeds in western Oregon. It aggressively displaces native plant species, dominates most riparian habitats, and has a significant economic impact on right-of-way maintenance, agriculture, park maintenance, and forest production. It is a significant cost in riparian restoration projects and physically inhibits access to recreational activities. It reproduces at cane apices (tips) and by seeds, which are carried by birds and animals. This strategy allows it to expand en masse across a landscape or jump great distances and create new infestations. Any control strategy can be considered short-lived unless projects are planned and funded for the long-term.”
Is the battle to control Himalayan blackberry utterly un-winnable? Maybe not. In spring 2004, Curry County farmers noticed a dieback in Himalayan blackberries. The plants looked like they had been sprayed with Crossbow. Upon closer inspection, experts determined the blackberries were diseased with Phragnidium violaceum, a blackberry leaf rust fungus. It appeared to be an accidental introduction, and the first official report of its presence in North America.

P. violaceum occurs naturally in wild blackberries in Africa, the Middle East, and Europe. It has been used for decades as a biological control in Chile, Australia, and New Zealand. Fungal spores, appear as yellow powdery pustules on the underside of the leaves, attack in late spring or summer; one result is seasonal defoliation. Vigorous as they are, blackberry vines require many rust attacks over a number of years to impact their health.

Can P. violaceun be safely used as a biological control in Oregon, the number one commercial berry state in the U.S.? The wild Evergreen Blackberry (Rubus laciniatus) and the commercially grown “Everthornless” Thornless Evergreen Blackberry are susceptible to the rust, though none has been found on native Rubus or other cultivated varieties. Studies are underway to investigate whether the rust will negatively affect commercial berry crops, other commercial crops, or native species. Experts say at least five years of research are needed to determine if blackberry rust should be authorized as a biological control method.

(Source: Lecture by Amy Peters at 2006 Interagency Noxious Weed Symposium, Corvallis Oregon)