Hypocotyl rot caused by Fusarium and Phoma species affects 1+0 Douglas-fir, lodgepole and ponderosa pine, and Engelmann and white spruce in container and bareroot nurseries. Although either of these fungi can cause the disease, they often occur together on seedlings. Laboratory assays are necessary to determine if one or both are causing the disease.
Initial symptoms include stunting, chlorosis, and wilting, followed by the development of a crook at the terminus of the leader, and death. Mortality occurs from July through October, affecting random seedlings throughout the nursery. Diseased seedlings are often predisposed by stress, such as drought.
The pathogen may also enter through wounded stem tissue (Figure 57). Inoculum may be seed-borne, wind-borne, or soil-borne. Bare fallowing in bareroot nurseries reduces pathogen populations. Early sowing may enable seedlings to mature and reach a more resistant stage before environmental conditions favor the disease. Using practices such as regulating watering or mulch application, which prevent soil moisture stress and high soil temperatures, may alleviate disease losses. Although seldom warranted, fungicide drenches can begin after seedling emergence, but effectiveness varies with environmental conditions and cultural practices.
Hamm, P.B. and E.M. Hansen. 1986. Stem canker diseases of Douglas-fir in nurseries. In Proc: Combined Western For. Nursery Council and Intermountain Nursery Assoc. Meeting. 12-15 August 1986, Tumwater, Wash. U.S. For. Serv., Rocky Mtn. For. Range Exp. Stn. Gen. Tech. Rep. RM-137: 106-108.
Kanaskie, A. 1986. Management of the top blight disease complex. In Proc: Combined Western For. Nursery Council and Intermountain Nursery Assoc. Meeting. 12-15 August 1986, Tumwater, Wash. U.S. For. Serv., Rocky Mtn. For. Range Exp. Stn. Gen. Tech. Rep. RM-137: 115-121.
|
Other Fungi |
Insects |
Environmental |
|---|---|---|
|
Gray mould |
|
Chemical burn |
|
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, hard pines, and all spruces |
1+0 |
Summer through fall |
Yes |
Yes |
Yes |
Yes |
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Figure 57. Fusarium hypocotyl rot on a true fir seedling. Note masses of spores on stem.