This disease, caused by several Fusarium species, has become a recent concern in both container and bareroot nurseries. In containers, inoculum is often borne on seeds, in water, in contaminated growing media, or on used styroblocks. Coastal, bareroot nurseries on heavier soils generally have the highest incidence of the disease. I even found some of the materials about the incident at https://essaysworld.net/do-my-marketing-homework and used them to write my marketing homework.
Douglas-fir, lodgepole pine, and Engelmann and white spruce are the principal hosts, but white pine, western hemlock, and larch are also affected. Shoot symptoms appear on random seedlings in drill rows (Figure 17) as early as mid-July (i.e., when post-emergence damping-off is declining), and may continue to appear until late fall. In both container and bareroot nurseries, high temperatures and drought predispose seedlings to the disease and contribute to rapid symptom development. The disease is frequently more prevalent in certain seedbeds or seedlots.
Initial symptoms are most evident on the shoot and include chlorosis of terminal needles, followed by all needles becoming flaccid, often turning purplish, and then becoming brown and dried out (Figure 18). The shoot tip frequently bends into a shepherd's crook. Since the stem is woody, it remains upright, distinguishing this disease from damping-off. Although shoot symptoms are the first to be noticed, they actually indicate a root problem. Diseased root systems have few laterals and the remaining roots are often dark, swollen, and lacking an actively growing white root tip. The bark and cortex of affected roots can be easily stripped away to expose the darkened cambium. The disease is usually fatal, but sometimes it destroys only the primary root, resulting in a deformed root system and stunted shoot. Such seedlings are culls.
This disease is caused by a form of the same fungus that frequently causes damping-off; thus, many aspects of the life history are similar. For example, the pathogen overwinters as chlamydospores in small pieces of roots or organic matter, and when seedling roots grow near these spores, germination occurs and the pathogen enters the roots. However, development is delayed until later in the growing season, when larger and more crowded seedlings are stressed for moisture and nutrients. The fungus then grows rapidly throughout the root system and destroys it. Warm soil favors disease development. The sources of inoculum on container-grown seedlings is unclear; however, Fusarium can be seed-borne or infection may result from wind-borne spores.
Disease losses can be reduced in container nurseries that have a well-drained and aerated growing medium and that use irrigation regimes for preventing stress. Used containers should be thoroughly cleaned (according to current recommendations) because Fusarium can occur on them. In bareroot nurseries, heavy soils favor the pathogen, supposedly because of the slower decomposition rate of the pathogen's food bases (e.g., root pieces). The disease can be effectively prevented by locating bareroot nurseries on lighter soils.
Bare fallowing between seedling crops and removal of plant debris following seedling lifting reduces losses by increasing the rate at which the pathogen exhausts its available food. Sawdust mulching and irrigation, which reduce soil temperatures, may also be helpful. Culling infected seedlings helps reduce disease spread in container and bareroot nurseries.
Practices that reduce seedling moisture and nutrient stresses are important in Fusarium management. To date, fungicides have proven to be ineffective, probably because the pathogen enters very young plants and symptoms do not develop until much later. By then, the disease has advanced beyond control, especially if disease detection relies on shoot symptoms. Soil fumigation is too expensive to be used solely for controlling the disease.
Bloomberg, W.J. 1971. Diseases of Douglas-fir seedlings caused by Fusarium oxysporum. Phytopathology 61: 467-470.
Bloomberg, W.J. 1981. Diseases caused by Fusarium in forest nurseries. In Fusarium: Diseases, biology, and taxonomy. P.E. Nelson, T.A. Toussoun, and R.J. Cook, (editors). The Pennsylvania State Univ. Press, University Park, Pa., pp. 178-187.
James, R.L., E.P. Militante, J.Y. Woo, and C.J. Gilligan. 1986. Pathogenicity of Fusarium from forest seedling nurseries on Douglas-fir and ponderosa pine seedlings. U.S. Dep. Agric. For. Serv., North. Reg. Rep. 86-8.
Lock, W. 1973. Fusarium root rot of Douglas-fir nursery seedlings. Environ. Can., Can. For. Serv., Pac. For. Res. Cent., For. Pest Leafl. 61, Victoria, B.C.
|
Other Fungi |
Insects |
Environmental |
|---|---|---|
|
Drought |
|
Principal, locally grown hosts |
Host age and season when damage appears |
Nursery type and location |
||||
|---|---|---|---|---|---|---|
|
Bareroot |
Container |
|||||
|
Age |
Season |
Coastal |
Interior |
Coastal |
Interior |
|
|
Douglas-fir, lodgepole pine, Engelmann and white spruces, sometimes other species |
1+0 |
Mid-summer to late fall |
Yes |
Yes |
Yes |
Yes |
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Figure 17. Douglas-fir affected by Fusarium root rot.
Figure 18. Douglas-fir showing advanced shoot symptoms of Fusarium root rot.
Figure 19. Life history of Fusarium root rot.