How to protect your Colorado Blue, White, and Black Hills Spruce trees
What is needle drop?
Rhizosphaera Needle Cast, commonly referred to as Needle Drop, is a fungal disease that infects Colorado Blue Spruce. White Spruce and Black Hills Spruce are a bit more resistant to the infection but can also become susceptible in the cool, wet spring or humid summer. All of these evergreens are at greater risk for infection when they are under stress.
How to spot the disease
Check your spruce trees for signs of Needle Drop in the cool, wet days of spring and humid days of summer, times when conditions are most favorable for the disease. Here’s what you should know:
- LOWER BRANCHES: Because humidity is higher closer to the ground, Needle Drop begins in the lowest branches.
- COLOR: The first sign of infection is the yellowing of lower needles. If not treated at this stage, needles will turn purplish brown and will eventually drop.
- DROPPED NEEDLES: Needles that are shed by your tree can become a breeding ground for fungal spores that will infect new growth and may risk infection of nearby trees.
How to treat the disease
The key to successfully treating most any fungal disease is to bring it under control as early as possible. At the first sign of distress or disease:
- AVOID OVERHEAD WATERING: Provide adequate air circulation and try to keep the tree as dry as possible.
- SPRAY with Fungonil or Bordeaux Mix (copper-sulphate).