Yellow bands containing faint orange fruiting bodies distinctive of spruce needle rust. Courtesy of Tracey Olson, PDA
Chrysomyxa weirii (H. S. Jacks)
- Most spruce species susceptible
- In Pennsylvania, most commonly reported on Colorado blue spruce and its varieties, Serbian spruce, and Sitka spruce
Symptoms and Signs
- Pale yellow bands become visible on current-year needles
- Needles infected in previous year turn brown and defoliate
- Pale yellow bands with orange fruiting bodies (called telia) obvious on most recent growth; band will go entirely around needle and increase in color intensity as season progresses; discolored bands easiest to see on overcast days
- Bright orange telia mature and rupture on infected needles
Throughout the Year
- Infected trees may appear disfigured and have extensive needle discoloration, reduced growth, and premature needle drop
Causes of Similar Symptoms
- Mechanical damage from needle punctured by needle tips
- Cinara aphids
- Pesticide phototoxicity
Weir’s cushion rust (Chrysomyxa weirii) is the only species of spruce needle rust currently found in Pennsylvania. Infected current-year needles will exhibit pale yellow bands that go completely around the needle. Orange, immature fruiting structures may be visible within the band. This is easiest to see on an overcast day or on the shady side of the tree. Mechanical damage from pricking of needles during windy weather may mimic spruce needle rust. But, mechanical damage does not encircle the needle and usually has a darkened, wrinkled spot or indentation in the yellowed area. Around bud break, the mature, orange telia form on the discolored spots. Spores are yellow orange.
Another species of spruce needle rust, Chrysomyxa ledi, has been detected in surrounding states. The fruiting body of this fungus resembles white blisters on current growth and requires an alternate host.
Biology and Life Cycle
This species of spruce needle rust does not have an alternate host. All necessary spore stages are found on spruce. During the winter, the fungus is maturing inside the current year’s needles and faint yellow bands with developing orange telia can easily be seen, particularly on lower branches (Figures 1 and 2). As bud break approaches, telia become swollen and contrast with the green or blue of the needle (Figure 3).
Figure 1. Early symptoms of developing rust on Serbian spruce. Courtesy of Tracey Olson, PDA
Figure 2. Faint yellow and orange bands with maturing fungus inside needles. Courtesy of Tracey Olson, PDA
Figure 3. Swollen telia, or fruiting bodies (April). Courtesy of Tracey Olson, PDA
At bud break the blisters burst, releasing massive amounts of yellow-orange spores (Figure 4). Wind and splashing rain carry spores to newly emerging needles on the same tree or adjacent trees. The infection period can continue for 2–3 weeks after bud break, and infection rate increases with high moisture.
Figure 4. Spores being released from the ruptured needle surface. Courtesy of Tracey Olson, PDA
The disease cycle starts again with the newly infected needles harboring the disease until bud break the following year. Previously infected needles that have already dispersed spores will turn rusty brown (Figure 5), die, and drop from the tree in summer. Spores will not continue to be produced on dead needles.
Figure 5. Sporulation occurs during bud break. Courtesy of Tracey Olson, PDA
Disease Cycle Calendar (Single Year’s Growth of Needles)
Monitoring and Management Strategies
- Thoroughly inspect all seedlings before planting.
- Space trees to encourage drying.
- Control weeds to reduce the moisture level around the trees and to increase coverage if control measures are needed.
- Remove and destroy abandoned hosts around field to eliminate sources of inoculum.
- Scout trees in winter for yellow bands with orange spots in the center indicating infection. Scout on overcast day or look at shaded needles to make it easier to detect discoloration. Lower branches are often first to be infected.
- If banding of needles is found, tag several trees to monitor for telia production.
- Scout trees for orange telia beginning 1–2 weeks before bud break and continue until 2–3 weeks after bud break.
- If only a few trees are found with symptoms, cut and remove them from the field well before fruiting bodies mature at bud break.
- Threshold level: No threshold level has been established for this fungus. If the fungus is present, it can spread rapidly with favorable environmental conditions.
- This can be a more serious concern for Christmas tree growers who also dig trees since it is a disease of regulatory concern for many states. Ask state/regional plant inspectors about a regulatory threshold for this disease.
- Apply a fungicide spray when trees have broken bud; make subsequent applications at weekly intervals until needles are mature or the symptomatic needles have dropped to the ground (approximately three to five sprays total).
- At the end of the season, evaluate results and update records.
- No recommendations are available at this time.
- Remove and destroy infected trees before spore production and release.
- No recommendations are available at this time.
Apply a fungicide spray when trees have broken bud; make subsequent applications at weekly intervals until needles are mature or the symptomatic needles have dropped to the ground (approximately three to five sprays total).
Do not purchase or accept infected nursery stock.