Needle cast (Rhizosphaera kalkhoffii) is a fungus disease affecting blue spruce trees in New Mexico. We have been identifying the disease right here in San Juan County!
Infections take place in the spring, but evidence of the disease is typically noticed late summer to fall. Symptoms of needle cast are discoloration of the needles, premature needle drop, and eventual defoliation. Infected needles turn yellow, then reddish-purple, and finally brown. Scattered lower branches are usually affected first and then browning progresses upward.
Timing is important! Needle cast disease overwinters in infected needles on the tree or ground. Spores are released from the infected needles in the spring. If your tree had needle cast symptoms in the fall it is time for treatment NOW.
Two years of treatment is recommended because of the organism’s life cycle, and will usually restore moderately affected trees to full foliage. Severely affected trees may require more years of treatment.
If you are unsure if your tree is infected, but it does not look normal, bring a clipped branch in a SEALED plastic bag to SJN for a diagnosis.
Tip: If trees are infected, fallen needles should be cleaned up and discarded in a sealed plastic trash bag and sent to the dump. Pruning shears should be sterilized with alcohol between cuts and between trees.