Warning This Web page has been archived on the Web.

Archived Content

Information identified as archived on the Web is for reference, research or recordkeeping purposes. It has not been altered or updated after the date of archiving. Web pages that are archived on the Web are not subject to the Government of Canada Web Standards. As per the Communications Policy of the Government of Canada, you can request alternate formats on the Contact Us page.

Fusarium root rot

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.

Hosts and damage

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.

Life history (Figure 19)

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.

Management

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.

Selected References

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.

Look Alikes

Other Fungi

Insects

Environmental

Corky root disease
Cylindrocarpon root rot
Pythium root rot

Fungus gnats
Weevils

Drought
Saturated Soil
High Salinity
Nutrient Deficiency

 

Summary

Fusarium root rot

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
rare on 2+0

Mid-summer to late fall

Yes

Yes

Yes

Yes

 


Figures

Click on any image to see the full size version. Press "Back" on your browser to return to this screen.


Click on this image to see a larger version     Figure 17. Douglas-fir affected by Fusarium root rot.

 

 

 

 


Click on this image to see a larger version     Figure 18. Douglas-fir showing advanced shoot symptoms of Fusarium root rot.

 

 

 

 


Click on this image to see a larger version     Figure 19. Life history of Fusarium root rot.