This nursery disease is caused by two fungi species. _Cylindrocladium
scoparium_ and _C. floridanum_: Cylindrocladium root rot has been found
on two hardwoods (yellow-poplar and black walnut) and two conifers
(white pine and Fraser fir) in forest tree nurseries in six southern
states. These include Virginia, West Virginia, North Carolina,
Tennessee, Alabama, and Mississippi.
[Illustration: Leaf symptoms on 1-0 black walnut nursery stock.]
Root rot symptoms on hardwoods and conifers are quite different. The
most characteristic root symptoms on yellow-poplar and black walnut are
the blackened and longitudinally-cracked infected roots that are in
sharp contrast with healthy white roots of these two species. Infected
seedling leaves become yellow and later turn reddish-brown.
Root rot symptoms on conifers involve either rotting of the seed or
seedling (pre-emergence damping off) before emergence from the soil or
seedling root rot following emergence. These symptoms also involve a
shrivelling and reddening of foliage, needle blight, and stem cankers.
The most characteristic symptoms are the “patchy” irregularly scattered
pattern of infection in conifer seedling beds and the loosening of the
root epidermis on infected roots—making it very easy to pull off.
[Illustration: Root symptoms on 1-0 yellow-poplar nursery stock.]
The most practical and effective control for root rot diseases of this
type involves strict quarantine to either keep the disease out of the
nursery or keep it confined to known infected areas by avoiding the
transportation of root material, organic matter, and soil from infected
to non-infected seed beds. Soil fumigation may control this disease if
applied under favorable conditions.