Spruce (Picea spp.)-Rusts

Latest revision: 
March 2023


Cause Chrysomyxa sp., a fungus. Species reported from the Northwest include C. arctostaphyli (spruce broom rust, with kinnikinnick as the other host); C. ledicola (with labrador-tea, Ledum sp., as the other host); C. piperiana (with Rhododendron macrophyllum as the other host); and C. weirii, which does not need an alternate host. The teliospores germinate in spring and form basidiospores, which the wind carries to young spruce needles. Infection is in wet weather. The orangish aeciospores that develop later in the year on these needles spread to the alternate host. Spores that develop from these infections (urediniospores) can reinfect the alternate host but not the spruce until teliospores form. C. weirii produces teliospores on last season's needles, which infect current-season needles.

Symptoms C. arctostaphyli causes large witches' brooms in spruce. Brooms lose the green of normal foliage and turn yellow during the year as opposed to witches' brooms caused by other pathogens that retain the color. Orange-yellow powdery rust spores form on the brooms' needles in summer. Needles are cast off in fall and winter. Brooms are associated with spiketops, dead branches, bole deformations, loss of annual growth increment, and death. On kinnikinnick, the rust is most noticeable in late spring when telia on leaf undersurfaces become orange-brown.

C. ledicola and C. piperiana prematurely defoliate spruce. Current-year needles develop a yellow-green discoloration that eventually becomes white outgrowths with orangish centers (aecia). These may be star-like when viewed individually on the needle surface. Needles drop from the tree making the crown seem especially thin. Labrador-tea and rhododendron develop orange-brown pustules (uredinia and telia) on upper leaf surfaces.

C. weirii also prematurely defoliates spruce but produces telia on last season's needles. These are orange, tongue-shape outgrowths from yellowed bands on the needles.

Cultural control

  • Remove the alternate host(s) from around plantings.

Chemical control

  • Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. Mancozeb-based products may provide some protection. Group M3 fungicides. 24-hr reentry.
  • Tourney EZ at 1 to 4 oz/100 gal water. 12-hr reentry.

Reference Ziller, W.G. 1974. The Tree Rusts of Western Canada. Canadian Forestry Service Publication 1329.