Spruce are beautiful landscape trees, but unfortunately for growers in Kansas, they are susceptible to several pathogens including Rhizosphaera needle cast. Rhizosphaera needle cast is a fungal infection that causes spruce to shed needles. This disease can leave spruce looking less than desirable and commonly causes death in lower branches and sometimes the entire tree if left unmanaged. Thankfully a little prevention and treatment goes a long way to keep trees healthy.
Rhizosphaera Biology and Identification
- Rhizosphaera is a fungal disease and thrives in moist to wet conditions.
- The fungus infects needles during wet conditions in spring but is not evident until later in the year.
- Symptoms usually start at the base of the tree and progresses upward.
- Needles may become yellow in summer and turn purple to brown by winter.
- Normally white stomata on the needles will become black.
- Infected needles fall off 12-15 months after infection giving trees a thin canopy. Spruce normally hold needles for 5 or more years therefore, premature needle loss stresses the tree.
Management of Rhizosphaera Needle Cast
- Reduce moisture on needles. Keep sprinklers away from trees.
- Space trees far enough apart to increase airflow.
- Reduce tree stress by watering (but not on the needles!), mulching, etc.
- Do not shear spruce trees as it will encourage dense compact growth which stays wet longer.
- Chemical treatment will not “cure” already infected needles but it protects young needles.
- Sprays should be applied when needles are 1/2 to 2 inches in length.
- Treatment should continue for 2 to 3 seasons.