How do I know if my spruce trees are infected?
On Colorado blue spruce, infected needles often show symptoms of yellow mottling in mid-to-late summer. Needles progressively turn bright yellow, purplish-pink and finally brown.
Infected needles of other plant species usually become off-green, later turning to tan or brown. As the fungus matures, rows of black fruiting bodies develop on the needles. Twelve to fifteen months after infection, needles will drop prematurely.
What causes needle cast?
Rhizosphaera needle cast is a very significant disease of landscape, nursery and plantation conifers. It is caused by a group of fungi in the genus Rhizosphaera. This disease is found throughout the northern hemisphere.
Cool, rainy weather or long periods of leaf wetness provide conditions for disease development.
Can needle cast kill my spruce trees?
Branches that lose first year needles for 3 to 4 consecutive years may die.
Which trees species are in danger?
Many spruce species, such as Colorado blue and Engelmann spruce are highly susceptible; white spruce is intermediate in susceptibility. Other hosts include: deodar cedar, Douglas fir, true firs, hemlocks, pines and coast redwood.
Management & Treatment Options
- Prune out severely affected branches.
- Rake up and dispose of fallen needles.
- Begin treatment with a registered fungicide in spring at half-needle elongation. Repeat when environmental conditions are conducive for disease development. Follow label rates and frequency for the product of choice.
- Deep root water during periods of drought.
- Fertilize with Arbor Green PRO to invigorate plant growth.