Fusarium top blight, caused by F. oxysporum, can cause severe losses of 1+0 Douglas-fir and pines in bareroot and container nurseries. In containers, the problem is often traced to seed-borne inoculum. Bareroot inoculum carries over on bits of old roots and organic matter, including sawdust mulch. On germinants, rot appears at the junction of the seedcoat and cotyledons and spreads down the stem. Seedling mortality follows.
Both bareroot and container-grown seedlings are attacked from mid-to late growing season. Symptoms consist of purplish, then brownish discoloration near the base of the succulent terminal leader, the terminal bud, or adjoining needles. The pathogen progresses downward (Figure 56) killing all or part of the stem and the needles.
In bareroot culture, the disease is most likely to occur on seedlings in older nurseries with heavier soils, because the pathogen builds up over the years and heavy soils favor pathogen survival. Situating nurseries on lighter soils alleviates this problem. Bare fallowing and frequent cultivation of bareroot soils between crops also helps reduce inoculum. The practice of roguing and culling diseased seedlings in both bareroot and container nurseries will help reduce pathogen spread. Fungicide sprays are sometimes used.
Buckland, D.C. 1947. Investigations on the control of Fusarium top blight of Douglas-fir seedlings. Can. Dep. Agric., Victoria, B.C. Unpubl. rep.
Salisbury, P.J. 1951. Investigations on the control of damping-off and top-blight of Douglas-fir seedlings at the Duncan forest nursery in British Columbia in 1948 and 1949. Can. Dep. Agric., Victoria, B.C. Unpubl. rep.
|
Other Fungi |
Insects |
Environmental |
|---|---|---|
|
Colletotrichum blight |
|
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 and pines |
1+0 |
Summer through fall |
Yes |
Yes |
Yes |
Yes |
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Figure 56. Fusarium top blight on container-grown Douglas-fir. Inthis case, inoculum was not seed-borne.