Thursday, April 24, 2008

Landscape and Nursery - Rusts on Junipers

The following is information on two common rusts that affect Junipers in Delaware.

CEDAR-QUINCE RUST caused by the fungus Gymnosporangium clavipes. The orange-red swellings on the twigs will be very evident. This fungus infects groundcover junipers, Juniperus horizontalis, Juniperus scopulorum, and several others as well. On this host the swellings are often undetected and can persist for years. The galls are perennial on juniper and should be pruned out if possible. The alternate host is hawthorn, serviceberry, and several other rosaceous plants and causes deformed fruit and green twig dieback.

Cedar-quince rust on Juniper. Photo from the University of Massachusetts Extension.

CEDAR-APPLE RUST. Be on the lookout as well for the round woody galls on twigs and branches of eastern red cedar, Juniperus virginiana. During wet weather orange-red spore horns emerge. These gelatinous appendages produce the spores that infect apple and crabapple leaves at this time of the year. The best control on cedar is to prune out the galls to the extent that is practical. These cedar-apple rust galls can be pretty spectacular for fungi-philes.

Cedar-apple rust on juniper. Photo from the University of Nebraska, Lincoln, Plant Pathology

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

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