Rhizosphaera needlecast, Rhizosphaera kalkhoffii, is a fungal disease of spruce trees that affects trees growing outside of their native range. Rhizosphaera starts on the inner and lower growth and progresses upward through the tree. It can take up to 15 months for needles to show visible symptoms after the initial infection. Young trees may be killed by this disease, but usually branches die off after 3-4 consecutive years of defoliation, causing mature trees to look disfigured.
As with most fungal diseases, prevention is the key to maintaining your tree’s health. Cultural practices such as watering only the soil around the base of your tree, avoiding getting the needles wet, and applying three inches of wood mulch can help trees overcome mild infections.
How Is It Spread?
New rhizosphaera infections begin during wet weather when spores from infected needles on the tree, and those that have fallen to the ground, are splashed on to uninfected needles. The yellowish brown to purple discoloration takes one year or more to develop. Spores overwinter on one and two year old needles.
• Symptoms begin on the inner and lowest portion of the tree and progress upward.
• Two year old needles turn yellowish-brown to purple in mid-summer.
• Complete branches can die back.
• A spruce with severe rhizosphaera needle cast may have only the current year’s needles left on the tree; healthy spruce will retain needles for 5-7 years.
Growing outside normal range, excessive watering
Risk Of Spreading