Circular 1189
Southern Pines 1
This document describes the history, biology, causes and current management of fusiform rust - the most serious disease of southern pine.Introduction .
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 50's and early 60's. Fusiform rust is estimated to cause 35 million dollars in losses annually in five Southeastern states, including 8 million dollars in Florida.
Figure 1. Galls on loblolly pine covered with aecisospores that will infect emerging oak leaves in the spring.
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:
Susceptible Species
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 or nearly so. 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 learned about the factors which enhance or inhibit rust increase and spread.
Pine Regeneration and Growth . Since World War II wide spread regeneration efforts have replaced oldgrowth 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 . The 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 oak to infect pine. 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 oaks.
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).
When a young plantation is infected, there are few remedies to reduce economic losses. Thus, preventing rust infection is most important. Managementrecommendations vary in high versus low rust hazard areas and risk must be evaluated.
At the site to be planted, the potential risk of rust occurrence may be defined as follows:
(1) high-rust hazard >30% trees infected* (approximately > 15% stems infected at age 5 years)
(2) moderate-rust hazard = 10-30% trees infected* (approximately 5-15% stems infected at age 5 years)
(3) low-rust hazard = <10% trees infected* (approximately <5% stems infected at age 5 years)
*Percentage trees infected are those with a stem gall or branch gall on a living branch within 12 inches of 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 1). 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.
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:
(1) Some forms of mechanical site preparation promote development of oak
sprouts (KG +disking reduces oak sprouts; chopping alone enhances oak sprouting
in young plantations)
Table 1. Estimating fusiform rust hazard risk
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 and federal laboratories and the forest industry and
are available at many nurseries.
Figure 2.
Fusiform rust galls on nursery seedlings.
Although 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 to 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 sedlings 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. Prescribed fire can provide effective oak
control inestablished stands, but resinous stem galls can be ignited resulting
in tree death.
Remember though, that because spores are wind-disseminated over great distances
(perhaps ½ 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 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 be appropriate.
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 sand.
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 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 burns) which could favor the establishment of susceptible oaks,
should be avoided (see Site Preparation and Oak
Management , above).
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, the 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 Thinnings , below).
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 pulpwood.
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,
when done 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 are extremely
susceptible to fusiform rust in some areas of their range and significant
losses occur.
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.
1 .This document is 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.
2 .Robert A. Schmidt, Professor, Forest Pathology,
School of Forest Resources and Conservation, Cooperative Extension Service,
Institute of Food and Agricultural Sciences, University of Florida, Gainesville,
32611.
Hazard or Risk
Nearby pine stands
Susceptible oaks
Soil type
Site quality/growth
High
>= 30% infected
Abundant in and around plantation
Moderately to moderately well drained
High/good growth
Moderate
10-to-30% infected
Present in or around area but scattered and not abundant
Poorly to moderately well drained
Moderate/good growth
Low
<10% infected
Lacking or few within 1/2 to 1 mile
Poorly drained flatwood spodoosols
Low/poor growth
Excluding Rust in Low Risk Areas
Treating Infected Stands
Summary
References
