Roadside Revegetation

IMPLEMENTATION GUIDES
Inset 10-18 | Assessing poor quality nursery stock
Poor quality planting stock can be caused by biotic (e.g., diseases,
insects) or abiotic factors (e.g., imbalance of soil moisture, temperature,
nutrients, and pesticides) in the nursery resulting in detrimental, and
sometimes devastating, effects on seedling survival and growth when
outplanted. Infection with various pathogens, or biotic causes, may
not necessarily be manifested in a nursery, but may cause stunting
or mortality once seedlings are under stress following outplanting.
Revegetation specialists should be aware of the possible nursery
diseases in order to either recognize or discuss with nursery personnel
during visits to inspect their seedlings.
Diseases caused by fungi, water molds, bacteria, and viruses can often
be difficult to distinguish from damage caused by abiotic events or
factors. If damage or chlorosis of seedlings is noted, it is recommended
to check with the nursery manager to determine the history of the
seedlings, what pathogens are traditionally a problem at the nursery,
and what, if any, have occurred during the current growing season.
Hamm and others (1990) and Landis and others (1990) provide more
detailed information on nursery pests.
Shoot and foliage diseases can be caused by a variety of organisms,
with various levels of impact on seedlings. Fusarium hypocotyl rot
(caused by Fusarium oxysporum) can cause large losses in the nursery
from July through October. Gray mold (caused by Botrytis cinerea) can
cause significant damage to densely grown bareroot and container
seedlings, as well as nursery stock stored in less than optimal conditions
(Hamm and others 1990). The mycelium and gray spore clusters are
often easily visible to the naked eye. Botrytis can girdle infected
seedlings, increasing mortality rates following outplanting. Minor
shoot and foliage diseases, such as shoot blight (caused a number of
organisms including Sirococcus spp., Phomopsis spp., and Phoma spp.)
and needle-casts and other foliage diseases tend to deform or stunt
seedlings, but do not result in significant mortality in the nursery or
in an outplanting situation.
Root diseases may be the most insidious of nursery seedling diseases.
Since seedlings are cultured under optimum conditions for growth,
symptoms are often masked throughout the growing season, manifested
only during outplanting stress or drought stress in succeeding
years. Most conifers, and many native species, are susceptible to root
diseases and root rots caused by Phytophthora spp., Fusarium spp.,
and Cylindrocarpon spp. These diseases will be manifested in the
nursery in pockets of symptomatic seedlings or mortality, particularly
in areas of poor drainage or previous infestation. Outplanting seedlings
infected with these pathogens will result in reduced survival. In
addition, transfer of these organisms to outplanting sites may result
in infection of the planting area. This specifically is a problem with
the root disease, Phytophthora lateralis. The spread of this disease
from infected seedlings can devastate populations of established
Port Orford cedar.
Not all seedling quality problems are caused by biotic factors – many
are one-time damaging events that occur during a short time span with
a regular distribution throughout the field or greenhouse (Mallams
2006). If foliage discoloration, foliage or stem wilting or die-back,
seedling stunting, or mortality occur in large patches or over large areas
in the nursery, the causes are often abiotic. Outplanting seedlings that
have been stunted or damaged in the nursery can reduce seedling
growth and survival, as well as increase the time required for site
recovery. However, the symptoms of abiotic damage are often more
apparent, and the consequences more easily predictable, than damage
caused by pathogens.
Although restoration personnel have little to do with nursery cultural
practices and disease mitigation in the nursery, several options exist
to prevent or control disease problems on restoration sites. Disease
mitigating measures are similar to insect mitigating measures: (1)
only plant healthy stock because weakened or stressed seedlings
are more susceptible to diseases both in the nursery and on the
outplanting site, (2) plant a variety of species to avoid outplanting
failure due to infestation of any single disease, (3) create a healthy
soil environment – seedlings grown on poor sites or on sites outside
of the species environmental ranges will be placed under stress and
more susceptible to disease infection.
Large container stocktypes (typically those equivalent to a half gallon or larger) are stored and
transported in the containers in which they are grown. They are typically stored in shadehouses
or other sheltered storage. In cold climates, the roots should be insulated to protect against
cold injury. During unseasonably warm periods during the late winter or early spring, large
container stock should be monitored for drying and irrigated if necessary.
Grading Specifications – There are no nursery-wide minimum nursery standards for the size
and appearance of nursery grown plants because of the wide variety of ages, stocktypes, and
growth patterns of native species. Nevertheless, you must establish some criteria for accepting
or rejecting plants or you might be receiving marginal plants. Being present at the time of
packing is the most effective way to negotiate grading standards with the nursery and assure
that you receive quality plants.
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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