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6F36c- UNIVERSITY OF
Cooperative Extension Service
Institute of Food and Agricultural Sciences
Management of Fusiform Rust Diseases of Southern
Robert A. Schmidt2
This document describes the history, biology,
causes and current management offusiform rust-the
most serious disease ofsouthern pine.
Fusiform rust, a fungus-caused disease which kills
and deforms pines, has been present in epidemic
proportion in slash and loblolly pine plantations
throughout extensive areas of the South, including
north Florida, since the late '50s and early '60s.
Fusiform rust is estimated to cause 35 million dollars in
losses annually in five Southeastern states, including 8
million dollars in Florida.
Research in state and federal agencies and forest
industry has provided management recommendations
to minimize losses to fusiform rust.
The important points of the life history of the
fusiform rust disease are:
the fungus pathogen, Cronartium quercuum f.
sp.fusiforme, requires two living host trees-
pine and oak-to complete its life cycle. The
fungus cannot spread from pine to pine
the fungus produces five distinct spore types,
each with a unique function: two types on
galls of pine stems and branches and three
types on the underside of oak leaves
young oak leaves are infected in the spring by
wind-borne spores produced on pine, and new
pine growth is infected later in the spring by
wind-borne spores from oak leaves.
Pines. Of the commercially important pine
species, slash pine, and loblolly pine are very
susceptible to fusiform rust; longleaf pine is less
susceptible; and shortleaf pine is immune. Sand pine is
not susceptible to fusiform rust, but is damaged by a
related pine-oak rust disease.
Oaks. More than 20 of the southern red oaks can
be infected by the fusiform rust fungus. The most
important oak hosts, especially in Florida, are thought
to be water, laurel, willow and southern red oak.
Cherry bark, bluejack, runner and blackjack oaks could
be important hosts in some areas.
Environmental factors (climatic, edaphic, and
biotic) including human activities, significantly affect
pathogens and the diseases they cause and fusiform
rust is no exception. Through research, much has been
1. This document is Circular 1189, one of a series of the School of Forest Resources and Conservation, Florida Cooperative Extension Service, Institute
of Food and Agricultural Sciences, University of Florida. First published: August, 1997. Please visit the FAIRS Web site at http://hammock.ifas.ufl.edu.
2. Robert A. Schmidt, Ph.D., professor, Forest Pathology, School of Forest Resources and Conservation, Cooperative Extension Service, Institute of Food
and Agricultural Sciences, University of Florida, Gainesville, 32611.
All chemicals should be used in accordance with directions on the manufacturer's label.
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ingredients. Mention of a proprietary product does not constitute a guarantee or warranty of the product by the author or the publisher.
The Institute of Food and Agricultural Sciences is an equal opportunitylaffirmative action employer authorized to provide research,
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or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office.
Florida Cooperative Extension Service I Institute of Food and Agricultural Sciences I University of Florida / Christine Taylor Waddill, Dean
UNIVERSITY OF Fl;u.',,S Li
Management of Fusiform Rust Diseases of Southern Pines Page 2
learned about the factors which enhance or inhibit rust
increase and spread.
.ENCE Pine Regeneration and Growth. Since World
SA RAYWar II widespread regeneration efforts have replaced
old-growth forests and have resulted in extensive areas
of young, rapidly growing, susceptible slash and
loblolly pine plantations. This most successful
regeneration effort has significantly altered the species-
and age-composition of the pre-existing forest, in favor
of the rust pathogen and resulting disease.
Most practices which improve pine growth, e.g.,
fertilization, vegetation (competition) control, genetic
growth rate improvement, and intensive site
preparation can favor rust development. This presents a
dilemma to forest landowners when rapid reforestation
and increased productivity are management goals.
Susceptible Oaks. Red oaks, which serve as the
source of the infection of pine, are critical for disease
development. Generally, the potential for rust on pines
increases with the abundance and nearness of infected
oaks. However, because the spores are microscopic in
size, produced in great abundance, and wind-borne,
they are transported in large quantities over long
distances from oaks to infect pines. Pines growing one-
half mile or more from infected oaks can be infected.
Soils. Moderately to well-drained soils with a
sandy surface and an organic horizon, but lacking a
spodic horizon, are associated with high rust incidence,
while the wetter, poorly drained, flatwood soils with a
spodic horizon are associated with low rust incidence.
These relationships exist because the better-drained
soils support an abundance of the alternate oak host,
while the poorly drained flatwood soils do not favor
Climate. Unfortunately, over extensive areas of
the Southeast, both moisture and temperature are
favorable for disease development much of the time.
This is especially true in young pine plantations where
abundant plant surface moisture occurs for long
periods during the critical spring season when
sporulation and infection occur.
Genetic Planting Stock. Species of pine and,
more importantly, some genotypes (families) within
slash and loblolly pine vary in their susceptibility or
resistance to fusiform rust. Planting rust-susceptible
pines increases the risk to fusiform rust, especially in
high rust incidence areas (see Rust-Resistant Planting
Stock and Nursery Planting Stock below).
Management of Fusiform Rust to
When a young plantation is infected, there are few
remedies to reduce economic losses. Thus, preventing
rust infection is most important. Management
recommendations vary in high versus low rust-hazard
areas and risk must be evaluated.
Evaluating Rust-Hazard Risk
At the site to be planted, the potential risk of rust
occurrence may be defined as follows:
* high rust-hazard= >30% trees infected* (approx.
2 15% stems infected at age 5 years)
* moderate rust-hazard = 10-30% trees infected*
(approx. 5-15% stems infected at age 5 years)
* low rust-hazard = <10% trees infected* (approx.
s5% stems infected at age 5 years)
*Percentage trees infected are those with a stem gall or branch
gall on a living branch within 12" the main stem.
Rust hazard can be assessed by defining critical
factors, e.g., 1) amount of rust in nearby susceptible
pine stands, 2) presence of susceptible oaks, 3) soil
type, and 4) site quality (see Table). In addition to
assessing risk, the product objectives of the landowners
should be considered: recommendations could differ
for short-rotation pulpwood as compared with longer-
rotation solid wood products.
Preventing or Reducing Losses in High-Risk
Site Preparation. Site preparation decisions
illustrate the dilemma regarding rapid growth and its
association with increased rust susceptibility. Site
preparation should follow rules of good silviculture,
especially as related to soils, and be compatible with
landowner objectives and capital. That is, fertilizer,
weed control, cultivation, and bedding (when
appropriate on poorly drained soils) will promote rapid
growth and increase productivity. However, it will
likely increase the percentage of rust-infected trees.
One added advantage of intensive management is
the opportunity to reduce on-site oak--chemically or
mechanically. Avoid site-preparation practices which
may increase or retain oaks on high hazard sites:
Management of Fusiform Rust Diseases of Southern Pines
Management of Fusiform Rust Diseases of Southern Pines Page 3
* Some forms of mechanical site preparation
promote development of oak sprouts (KG +
disking reduces oak sprouts; chopping alone
enhances oak sprouting in young plantations)
* windows, which incorporate large amounts of soil
and prevent complete burning of piled debris, may
create soil conditions in the window, which favor
Prescribed fire can provide effective oak control in
established stands, but resinous stem galls can be
ignited resulting in tree death.
Remember though, that because spores are wind-
disseminated over great distances (perhaps '2 to 1
mile), there is no assurance that removing oak from a
plantation and immediate surrounding area will
significantly reduce rust incidence. Spores may still
Table. Estimating fusiform rust-hazard risk.
Hazard or Nearby pine Susceptible oaks Soil type Site quality/growth
High >30% infected Abundant in and around Moderately to moderately well High/good growth
Moderate 10-to-30% Present in or around area but Poorly to moderately well Moderate/good growth
infected scattered and not abundant drained
Low <10% infected Lacking or few within %-1 mile Poorly drained flatwood Low/poor growth
Rust-Resistant Planting Stock. The best
management tool to prevent or reduce rust losses is
rust-resistant seedlings. Rust-resistant varieties
(families) of slash and loblolly pine have been
developed by research scientists at state, federal, and
forest industry laboratories and are available at many
Large quantities of the best rust-resistant seed are
in short supply and some rust-improved varieties are
more resistant than others. Rust-resistant seedlings can
reduce rust incidence by 20-80% in high rust-hazard
areas, with little or no reduction in growth.
Due to their short supply, rust-resistant seedlings
should only be used in moderate to high rust-hazard
areas. Caution is urged: not all genetically "improved
seedlings" have rust-resistance; some are only
improved for growth. These seedlings would be a poor
choice to plant in high rust-hazard locations.
Planting Healthy Seedlings. In most nurseries
(especially those in high rust-hazard areas) fusiform
rust is effectively controlled with the systemic chemical
Bayleton. Bayleton is not recommended
subsequent to outplanting, except in special
circumstances, e.g. seed orchards, ornamental trees, or
trees in research plots.
Oak Management. Reducing the abundance of
oaks should be encouraged as part of the standard
operational procedures during harvest and plantation
establishment. Oak control is a factor not only because
pine-infecting spore come from infected oak, but oak
control will aid in reducing hardwood competition.
come from beyond the oak removal zone. So, reducing
oak solely for the purpose of reducing rust incidence
may not be effective.
Delayed Fertilization. In high hazard areas, it
may be possible-depending on soil type or landowner
objectives- to delay fertilization until mid-rotation in
order to prevent the rapid growth and associated
susceptibility of young trees when they can be severely
impacted by early developing stem cankers. For
example, on soils that do not require early fertilization
for seedling survival or in management systems for
longer, solid wood rotations, delaying fertilization may
Alternative Species. On appropriate sites,
longleaf pine, thought to be more naturally resistant to
the fusiform rust fungus, or the naturally immune
shortleaf pine may be good alternatives for planting.
Sand pine is a good alternative on deep sands.
Excluding Rust in Low Risk Areas
Little need be done on low rust-hazard sites. Rust
incidence, especially damaging stem cankers, will
likely be infrequent and losses will be minimal.
However, there are two precautions which should be
observed. These concern rust-free planting stock and
the invasion of susceptible oak hosts.
Nursery Planting Stock. Given that there is, at
present, a limited supply of highly resistant seedlings,
fast growing families (genetically improved seedlings)
lacking rust resistance are best planted on low rust-
Management of Fusiform Rust Diseases of Southemn Pines
Management of Fusiform Rust Diseases of Southern Pines Page 4
hazard sites. However, because these seedlings are
susceptible, growers should insure that seedlings are
obtained from a nursery which protects trees from rust
infection prior to lifting. Otherwise, infected seedlings
with or without visible galls (latent infections) may be
planted and trees will die early in the rotation.
Further, if these infected trees sporulate before
they die, they could introduce rust into an otherwise
rust-free area and increase the rust hazard of the site,
creating problems for the current and future plantings
(see Planting Healthy Seedlings, above).
Encroachment of Oak. It is important that low
hazard sites without significant numbers of oak remain
so. Thus, harvest and site preparation practices
(including drainage to reduce soil moisture and
elimination of control bums) which could favor the
establishment of susceptible oaks, should be avoided
(see Site Preparation and Oak Management, above).
Treating Infected Stands
Stands which have become infected can be
managed or treated in several ways to reduce losses.
Replant. If a young plantation is severely infected
(>50% stems infected prior to age 3 to 5 years),
consideration should be given to destroying the
plantation and replanting with resistant seedlings,
especially if landowner objectives are for pulpwood.
It is not advisable to remove diseased trees and
interplant since the newly planted trees will not
compete well with the older established trees.
Another alternative might be to manage for fewer
stems and longer rotations, e.g., for solid wood
products. In this case, severely infected trees, those
with stem cankers or limb galls likely to grow into the
stem, could be removed in precommercial or
commercial harvests (see Sanitation/Salvage
Pruning Limb Galls. Because a large percentage
of limb galls within 12 inches of the stems on young
trees grow into the stem within a few years, it may be
beneficial to prune limb galls, thereby preventing
damaging stem galls. Currently, this practice is only
economically feasible on ornamental trees, but is
impractical for extensive plantings to be used for
If landowner objectives are for longer timber
rotation (sawlogs), pruning has added advantages and
may be economically feasible.
Sanitation/Salvage Thinnings. A sanitation/
salvage thinning at mid-rotation age or beyond should
remove diseased trees. This practice, in conjunction
with normal thinning operations, can improve the
residual stand and utilize trees which otherwise would
likely be lost before normal harvest age.
Thinnings should be carefully considered,
however, to avoid residual pines being attacked by the
annosum root rot fungus and/or southern pine beetle, if
these pests are present in the area and/or environmental
conditions are favorable for pest attack.
Intensively managed plantations of loblolly and
slash pine in some areas of their range are extremely
susceptible to fusiform rust and significant losses
The critical factors which influence fusiform rust
development are rapid young tree growth, presence of
susceptible oaks, moderate to well-drained soil
conditions, and a warm, moist climatic. Management
of fusiform rust to reduce losses begins with evaluating
the rust-hazard risk of a site. Preventing or reducing
losses in high rust-hazard areas involves site
preparation which reduces oak populations, planting
rust resistant and rust-free slash and loblolly pine
seedlings, and delaying fertilization or planting
naturally resistant species. In low hazard areas,
planting healthy (rust-free) seedlings and insuring that
silvicultural practices do not encourage oaks is advised.
Infected young plantations can be replanted, pruned or
thinned depending on the landowner's objectives.
Dinus, R.J. and R.A. Schmidt, eds. 1977. Management of
fusiform rust in Southern pines. Symp. Proc., Univ. Fla.,
Gainesville. 163 p.
Powers, H.R., Jr., T. Miller, and R.P. Belanger. 1993.
Management strategies to reduce losses from fusiform rust.
South. J. Appl. For. 17:146-149.
Management of Fusiform Rust Diseases of Southern Pines