Spruce needle cast (Lophodermium piceae)
- Latin name: Lophodermium piceae (Fckl.)
- French name: Rouge (Lophodermium piceae)
- Division: Ascomycota
- Class: Rhytismatales
This disease is widely distributed throughout the range of its hosts.
Damage, symptoms and biology
Needle cast is caused by a related group of fungi (Ascomycetes), which cause more damage to coniferous foliage in North America than any other group of fungi. Severe infection can result in significant growth reduction in seedlings.
Typically, only a few of the many needle cast diseases are known to cause serious damage which is limited to growth loss; tree mortality is not known. Seedlings may be severely damaged if a high percentage of the foliage is infected. Heavily infected trees have an unsightly appearance caused by needle discolouration.
The degree of damage can be influenced by the age of the host tree; older trees are more resistant to damage and infection of older needles is eventually harmless.
Lophodermium piceae causes damages on 2-year-old and older infected needles, which makes damage minimal. Sokolski et al. 2007 consider it an endemic endophyte in black spruce.
Climatic conditions influence spore dissemination and germination, and thus the frequency and severity of infection. Needle cast diseases are more common following wet springs. Lower branches and understory trees are frequently the most seriously affected as the more humid conditions favour infections.
Generally, two types of fruiting bodies develop during the life cycle of fungi responsible for needle cast:
"asexual" fruiting bodies, which occur as small dots (pycnidia) on the upper surface of the needles; and
"sexual" fruiting bodies (producing the ascospores that transmit the disease), which are generally larger and occur along the mid-ribs of the lower needle surface.
Each fungus responsible for needle cast has a different life cycle and many are incompletely known; that of Isthmiella faullii is presented as an example.
The current year's needles are infected first, but they do not show any damage. The following spring, brown spots appear, eventually covering the entire surface of the needles by mid-summer. The first fruiting bodies form on the upper surface of the needles and discharge spores in late summer or early fall. It is unclear exactly what role these spores play, but they may give rise to the second type of spores. Ascospores form in mid-summer on the needles infected two years earlier. The “sexual” fruiting bodies called hysterothecia (because the ascocarp has a slit-like opening), create a black line on the lower needle surface. During rainy periods, asci will release ascospores that are able to infect new shoots the following spring. The ascospores are dispersed by the wind. Prolonged wet periods contribute to infection.
No control measures are planned in the forest sector. However, Christmas tree growers might consider preventing infection on lower branches by clearing the base of trees and cleaning out grasses growing between rows in order to reduce moisture levels, thus minimizing conditions conducive to new infections. Keeping fir and spruce trees in windbreaks should also be avoided in order to reduce potential sources of inoculum. Lastly, chemical control using copper oxychloride-based fungicides (the only fungicide registered in Canada for controlling needle cast and rusts) applied every 10 days after bud break until wet spring conditions subside could be considered. This spraying should be done by trained personnel who have received the required training.
There are three species of true fir, Abies spp., in the Pacific region: amabilis fir, occurs west of the Coast Mountains; alpine fir, occurs generally above 1200 m along the Coast and is scattered throughout the Interior into the Yukon Territory, and grand fir, occurs at lower elevations on Vancouver Island and the adjacent mainland coast, inland to the Hope area, and in the southern region of the southwest Kootenays. Some of the many true fir needle and shoot blights also cause damage to Sitka spruce, and white spruce foliage.