IDENTIFICATION

Rhizosphaera needle cast is a foliage disease of spruce trees. This tree disease generally starts at the bottom of the tree and progresses upward. Older, inner needles of the spruce tree branches are where disease symptoms are first seen. Infected needles first appear mottled or speckled with small yellowish spots. Eventually, the infected spruce needles turn a brownish to purplish color. Spruce needles may be dropped (cast) anytime from 3 to 15 months after the initial infection, depending on the variety of spruce infected. Under close examination distinct black specks can be seen in rows on the discolored needles. These specks contain the spores that spread the disease throughout the tree. The spores are spread by dripping and splashing water.

Infection from Rhizosphaera needle cast can occur anytime during the growing season on current growth or older needles that are stressed due to other pests or environmental conditions. Prolonged periods of moisture are required for the spores to germinate and initiate infection. Trees that are crowded together and/or are frequently hit by water from sprinkler systems are subject to severe needle cast infections.

HOW TO CONTROL RHIZOSPHAERA NEEDLE CAST

Rhizosphaera needle cast attacks non-native tree species or stressed trees growing in nutrient poor soils or under adverse conditions. The first step in treatment is to improve the conditions in which the tree is growing. This usually involves fertilizing to provide nutrients to invigorate a tree that is struggling. Proper watering is also essential to avoid stressing the tree either through drought or over watering. Be careful when watering spruce trees. It’s important to avoid letting water spray the tree branches, as this creates conditions favorable to growth and spread of this tree disease.

Three or more fungicide treatments in the spring and throughout the summer will help protect newly emerging spruce needles. Previously infected needles will continue to be lost even after fungicide treatments have begun, and infected needles may remain on the tree for up to 15 months. It may be necessary to continue the disease prevention program for up to five years to fully control the disease while the tree's vigor is regained. On some sites the environmental conditions may cause the disease to become chronic, requiring annual fungicide treatments.

HOST TREES

Colorado Blue Spruce, Black Hills Spruce, Norway Spruce, White Spruce.

CONTRIBUTING FACTORS

Rhizosphaera attacks non-native and stressed trees growing in nutrient poor soils or under adverse conditions. Prolonged exposure to moisture and trees that are crowded are most subject to fungal infection.

This tree disease generally starts at the bottom of the tree and typically moves upward throughout the tree canopy. Infected needles first appear mottled or speckled with dull yellowish blotches. Later, the needles turn brown to purplish brown. The needles are then dropped or “cast” from the tree. Under close examination distinct black specks can be seen in rows on the discolored needles and these specks contain the spores that spread the disease throughout the tree.

LIFE CYCLE

Disease infection usually occurs in the spring when moist weather conditions are most prevalent. Symptoms may be seen in the fall, but most often are not apparent until the following spring.

MANAGEMENT

Reducing tree stress by Deep-Root Fertilizing to help promote health and vigor.

Proper watering is essential to avoid stressing the tree by either over watering or causing drought.

Apply three or more fungicide treatments starting in the spring to protect new growth. Full control may not be achieved in one growing season because of the length of time infected needles remain on the tree.

Photos:  Joseph O'Brien, USDA Forest Service, Bugwood.org, USDA Forest Service - North Central Research Station Archive, USDA Forest Service, Bugwood.org