Fusiform Rust Disease of Southern Pines: Biology, Ecology and Management
Robert A. Schmidt, Professor, School of Forest Resources and Conservation, University of Florida
 
Contents
Development of the Fusiform Rust Epidemic
Losses to Fusiform Rust
Biology of the Fusiform Rust Pathosystem
Life History
Susceptible Species
Pines
Oaks
Ecology of the Fusiform Rust Pathosystem ­ A Rust Favorable Environment
Natural Old Growth Forests Contrasted with Intensively Managed Plantations
Critical Factors
Pine Regeneration and Growth
Susceptible Oaks
Soils
Climate
Improved Planting Stock
Management of Fusiform Rust to Reduce Losses
Evaluating Rust Hazard Risk
Reducing Losses in Moderate- and High-Hazard Areas
Site Preparation
Rust-resistant Planting Stock
Plant Healthy Seedlings
Oak Management
Delay Fertilization
Alternative Species and Silviculture
Preventing Rust in Low-Hazard Areas
Nursery Planting Stock
Encroachment of Oak
Treating Infected Stands
Replant
Prune Limb Galls
Sanitation/Salvage Thinnings
Benefits of Research
Summary
References
Acknowledgments
 

Development of the Fusiform Rust Epidemic

Fusiform rust, a fungus-caused disease which kills and deforms pines (cover photo), has increased to epidemic proportion in slash and loblolly pine plantations throughout extensive areas of the South, including north Florida, since the late 50s and early 60s. Previously, this disease, first reported near the turn of the century, was neither widespread nor prevalent. There is evidence the disease increased in intensity from Mississippi to the Atlantic coast and south to Florida. The pathosystem is endemic (i.e., both host and pathogen are indigenous to the southeastern USA, which is likely the center of origin and the region of great genetic diversity in host and pathogen). The pathogen is not known to occur naturally outside the southern USA and is most prevalent in the southeastern USA. The increase in fusiform-rust incidence and therein its role as a major limiting factor in the management of slash and loblolly pine over extensive areas resulted from changes in the forest ecosystem which occurred as pine management evolved from extensive to intensive.

The fungus causing fusiform rust is not favored nor abundant in old growth natural stands but is greatly favored in young, rapidly growing, pine plantations of susceptible species, especially when established in high- rust hazard areas. Young plantations are extremely vulnerable to the disease in high-rust hazard areas and more than 90% of rust-susceptible trees can be infected by the age of 5 years. Also, land-use patterns which placed susceptible pines in close proximity to the alternate host (susceptible oaks), (e.g., planting slash and loblolly pine on former agricultural land where oaks abound) favored fusiform-rust increase, as did a reduction in controlled burning and suppression of wildfires, which favored oak abundance. Research by state and federal agencies and the forest industry, which began in the 50s, continues to improve our knowledge of the biology, ecology and management of this most serious disease of southern pines.

Current rust hazard zones for fusiform rust in plantations of slash and loblolly pines (Figures 1A and 1B) show areas of low, moderate and high-rust hazard (see Table 4 for delineation of rust hazard). Fusiform rust is estimated to cause 35 million dollars in losses annually in five southeastern states, including 8 million dollars in Florida. Table 1 shows the number of acres by forest type in Florida with high, moderate and low levels of rust-infected trees.March 1998
 
 
Table 1. Thousands of acres of pine forests in Florida with fusiform rust at three levels of incidence (adapted from Starkey et al. 1997). 
Rust incidence 1 
 

Forest type 

  

Total acres 

 >10%  >30%  >50% 
Acres  Acres  Acres 
#  %  #  %  #  % 
Planted slash  3296  794  24 2  274  8  121  4 
Natural slash  1903  158  8  58  3  30  2 
Planted loblolly  317  99  31  60  19  31  10 
Natural loblolly  261  116  44  63  24  30  11 
Total/Average  5777 3  1167  20  455  8  212  4 
1 Rust incidence is % trees with a stem gall (canker) or a branch gall within 12 inches of the stem. 
2 % rounded to nearest whole number. 
3 Of the total pine acres (5,777,000) 36.5, 51.8 and 11.7% are in non-industrial, industrial and government ownership, respectively. 

Losses to Fusiform Rust

Annual losses to fusiform rust have been estimated at 35 million dollars in five southern states (FL, GA, SC, NC and VA) and 8 million dollars in Florida. Significant rust and losses also occur in AL, MS, and east TX (Figures 1A and 1B). Losses occur mostly as mortality to young pines. When 1-5-year old trees develop stem galls, they often die before rotation age (harvest) or become deformed and unmerchantable or reduced in value (cover photo).

Trees with severe stem galls ­ often referred to as cankers ­ may die throughout the rotation especially if subjected to high velocity winds. Branch galls on young trees within 12 inches of the stem often grow into the stem and become damaging stem cankers, otherwise branch galls which form on older trees or further from the stem do not severely impact the tree. Severely diseased trees may suffer a loss of growth in the absence of mortality. In high-rust-incidence areas, severely damaged young plantations are often destroyed and replanted, adding to costs of establishment and lengthening rotation age. Further, rust-infected trees may succumb to other pest problems (e.g., pitch canker, pitch moth or tip moth).

Damage can also occur when resinous stem cankers (galls) ignite during prescribed burns or wild fires: these trees may be killed or reduced in value due to charring.

A model has been developed (Table 2) to estimate losses due to rust-associated mortality for unthinned slash pine plantations at age 20 years as a function of stem galls at age 5 years and site index (potential pine growth rate).

To discuss the management options available to large and small, private and public, forest landowners, some important attributes of the biology and ecology of the fusiform-rust pathosystem must be considered.
 
 
Table 2. Estimated number of trees surviving and volume loss to fusiform-rust-caused mortality for slash pine in unthinned plantations at age 20 years as a function of percentage stem galls at age 5 years and site index (adapted from Nance et al. 1982). 
Site index a 
40, 60, 80  40  60  80  80 
Stem rust age 5 yr  Surviving trees age 20 yrs  Volume loss - age 20 yrs 
(%)  ------(#/ac)------  -----------(cu ft/ac)-----------  cd/ac 2 
0  621  0  0  0  0 
10  555  33  142  347  2.7 
20  489  72  292  537  4.2 
30  424  118  424  794  6.2 
40  359  168  600  1114  8.7 
50  296  125  771  1474  11.5 
60  238  291  987  1914  15.0 
70  171  362  1251  2420  18.9 
1 Site index is a measure of the quality of a site and is quantified by the average height of the dominant (tallest) trees on the site at age 25 years. 
2 Loss based on 128 cu ft/cd; growth of 2 cd/ac/yr. 

Biology of the Fusiform Rust Pathosystem ­ A Complex Life-style

Life History

The life history of the fusiform rust pathosystem is complex (Figure 2).

The important aspects of the disease cycle are: 1) the fungus pathogen, Cronartium quercuum f. sp. fusiforme , is an obligate parasite requiring two living host trees ­ pine and oak ­ to complete its life cycle; the fungus cannot spread from pine to pine, but must return to oak to produce the spores which in turn infect pine; 2) the fungus produces five distinct spore types, each with a unique function ­ two types (pycniospores and aeciospores) occur on galls on pine stems and branches, and three types (urediniospores, teliospores and basidiospores) occur on the underside of oak leaves; 3) tender young oak leaves are infected in the spring by wind-borne aeciospores produced on pine, and new pine leaders are infected later in the spring by wind-borne basidiospores from oak leaves; 4) the fungus does not require a wound to infect the oak or pine hosts, but can infect emerging succulent, healthy host tissue, directly or through stomata; hardened tissue of oak and pine cannot be infected by the fungus; 5) spores of the fungus require moisture for germination and infection of pine and oak; 6) the fungus is perennial in living pine tissues, causing a hypertrophy or gall. The gall is often colonized by other fungi and insect pests which deteriorate and weaken the galled portion of the tree (Figure 3). The fungus is annual in oak leaves: dying with defoliation in the fall and recurring with infection of oak from the orange aeciospores produced on the pine galls in the spring. Little or no damage occurs to oak trees, although severely infected leaves may die.

Susceptible Species

Pines. Of the commercially important pine species, slash pine ( Pinus elliottii var. elliottii ) and loblolly pine ( P. taeda ) are very susceptible to fusiform rust; longleaf pine ( P. palustris ) is less susceptible, and shortleaf pine ( P. echinata ) is considered immune. Pond pine ( P. serotina ) is intermediate between loblolly and longleaf, and spruce pine ( P. glabra ) is essentially immune. Sand pine
(P. clausa ) is not thought to be susceptible to fusiform rust but is damaged by a related pine-oak rust disease.

Oaks. Twenty of the southern red oaks can be infected by aeciospores of the fusiform rust fungus (Table 3). The most important oak host in many areas in Florida is water oak ( Quercus nigra ) but prevalent and important oak species can vary among habitats. Several species of pine from the western U.S. and California black oak are very susceptible when artificially inoculated, but the disease does not occur naturally on these species.
 
 
Table 3. Relative susceptibility of southern oaks to Cronartium quercuum f. sp. fusiform (adapted from Dwinell 1974). 
Oak host 1  Rank 2  Oak Host  Rank 
Water  1a 3  Blackjack  6cd 
Willow  2a  Southern red  7cde 
Cherrybark  3b  Northern red  8de 
Bluejack  4b  Turkey  9de 
Running  5bc  Laurel  10ef 
1 Other oaks of lesser susceptibility are swamp chestnut, scarlet, overcup, chestnut, black, dwarf live, sand live, post and dwarf post. 
2 Ranked from most susceptible to least susceptible on the basis of number of telia/cm 2 of leaf surface area following artificial inoculation of seedlings. 
3 Ranks not followed by the same letter are significantly different (p = 0.05) for telia/cm 2 of oak leaf surface area. 
 

Environmental factors (climatic, edaphic and biotic) including human activities significantly affect pathogens and the diseases they cause. Fusiform rust is no exception. Research has identified certain critical environmental factors in the biology and ecology of the fusiform rust pathosystem, including management practices which can influence the rust epidemic and help to explain why the disease has reached epidemic proportions in intensively-managed pine plantations and naturally regenerated old fields.

Natural Old Growth Forests Contrasted with Intensively Managed Plantations

In the natural forest, essentially devoid of human activity, indigenous (native) pathogens and indigenous hosts most often reach a balance, such that both organisms co-exist without severely limiting one another. Such was the case historically (at least in the recent past) with fusiform rust in natural pine forests where this indigenous rust was of limited occurrence and caused little damage. Earlier unchecked natural fires and those set by Indians and early settlers likely limited oak populations and fusiform rust incidence. However, in our desire (and need) for more productive forests, with more intensive forest management, we have created conditions very favorable for fusiform rust to increase and spread. To redress the balance and reduce losses to fusiform rust, the critical factors which have caused increased rust incidence must be identified and their role in the epidemic understood. It should also be noted that natural forests newly seeded onto old fields also have a high incidence of fusiform rust. This is especially true of loblolly pine, often called "old field pine".

Critical Factors

Pine Regeneration and Growth.  Since World War II intensive planting efforts have replaced natural regeneration and 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 agecomposition of the pre-existing forest, in favor of the rust pathogen and resulting disease. Old growth forests ­ often of the more rust-resistant longleaf pine ­ were replaced by young plantations of the more susceptible slash and loblolly pines. For example, in Florida, pine plantations increased from an estimated 291 thousand acres in 1952 to 5.59 million acres by 1990. In the Southeast, this increase was from 1.0 to 22.6 million acres. The shift to younger age classes accompanying the increase in plantations has contributed greatly to the increase in rust incidence. Abundant, succulent, new pine growth (leaders) are very susceptible to infection by the fungus. While many pathogens grow best in weakened trees, the fusiform-rust pathogen infects and grows best in healthy, rapidly growing trees. The more rapidly a tree grows, the more it is at risk to the fungus. Thus, most practices which improve pine growth (e.g., fertilization, vegetative competition control, genetic growth rate improvement, and intensive site preparation) favor rust development. This presents a dilemma to forest landowners when rapid reforestation and increased productivity are management goals.

Susceptible Oaks .  The red oaks (Table 3), which serve as the alternate host of the pathogen and the source of inoculum (spores) for the infection of pine, are critical for disease development. In the absence of susceptible oaks, there would be no fusiform rust of pine since the fungus cannot spread from pine to pine. 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 apparently 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.

On the drier upland sites where oaks can flourish in the absence of fire, reduced prescribed burning and absence of wildfires, which has occurred over the last 50-70 years, has favored oak regeneration and allowed oaks and rapidly growing young pines to occur in close proximity. Incentive programs have resulted in an increase of planting of former agricultural sites (i.e., drier sites where oaks flourish). Also, some silvicultural practices can favor oak regeneration (see Site Preparation , below).

Soils.  Moderately to well-drained soils with a sandy surface and an organic horizon, but lacking a spodic horizon (CRIFF E & F soils) 1 , are associated with high-rust incidence, while the wetter, poorly drained, flatwood soils with a spodic horizon (CRIFF C & D soils) 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. Thus, soils are an indicator of oak and therein of rust hazard. This relationship, however, applies best to extensive areas and those unaltered by silvicultural practices which favor fusiform rust increase and spread, and soil samples alone cannot be relied on to predict rust hazard at the individual stand level due to long-distance dissemination of spores of the pathogen.

Climate . Fusiform rust has special climate requirements for rapid spread and development. Most important is surface moisture in the form of rain or dew on succulent oak leaves and pine leaders, which favor the production of spores, spore germination and subsequent infection of the hosts. 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. There is some indication that fusiform rust is limited in the west (Texas) and the north (NC) by a lack of sufficient moisture and low temperatures, respectively. It is also apparent that rust incidence varies among years depending in part on favorable or unfavorable weather at critical periods in the rust life cycle.

Improved Planting Stock . Species of pine and, more importantly, some genotypes 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 , below).

Management of Fusiform Rust to Reduce Losses

Proactive prevention of disease is a fundamental principle of effective forest disease control. This principle is especially appropriate for fusiform rust which causes most severe impact in young plantations. When a young plantation is infected, there are few effective remedies to reduce economic losses. Thus, preventing rust is most important. Management recommendations vary in high- versus low-rust hazard areas, and rust-hazard risk must be evaluated.

Evaluating Rust Hazard Risk

Prior to planting, the potential risk of rust occurrence can be described as follows:

<´> High-rust hazard : >30% pines infected* (approximately >15% stems infected at age 5 years). 

<´> Moderate-rust hazard : 10-30% pines infected (approximately 5-15% stems infected at age 5 years). 

<´> Low-rust hazard : <10% pines 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 (adapted from Starkey et al. 1997).

High- and low-rust incidence areas, which have remained so for many years (Figure 4) can be assessed by defining critical factors, e.g., 1) the amount of rust in nearby susceptible pine stands, 2) the presence of susceptible oaks, 3) the soil type, and 4) site quality (Table 4). 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.
 
 
Table 4. Estimating fusiform rust-hazard risk. 
Hazard or risk  Susceptible 
oaks 		 Rust in nearby pine stands  Soil type  Site quality/ 
Growth rate 
High  Abundant in and around plantation  > 30% infected  Moderately to moderately well drained  High-rapid 
growth 
Mod- 
erate 		 Present in or around area but scattered and not abundant  20-30% infected  Poorly to moderately well drained  Moderate- 
rapid growth 
Low  Lacking or few within ½ mile  < 10% infected  Poorly drained flatwood spodosols  Low-slow 
growth 
Data from row-plot progeny tests, which estimate rust impact, show the increase in rust incidence with age (Figure 5) and the associated rust mortality (RAM) at age 23 years given the percentage of trees infected at age 5 years.

For example, a plantation with 50% of the trees infected at age 5 years (R05) is predicted to have approximately 90% of the trees infected at a pulpwood harvest age of 23 years (Figure 5). This same plantation is predicted to have 35% rust associated- mortality (RAM) at age 23 years (Figure 6).

Reducing Losses in Moderate- and High- Hazard Areas

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. Site preparation practices which may increase or retain oaks on high-hazard sites should be avoided. Some forms of mechanical site preparation promote development of oak sprouts. For example, in one study KG (shearing standing, residual trees [following harvest] at or below the ground line) and discing promoted the fewest sprouts while chopping without discing promoted the greatest number of oak sprouts (Figure 7). Site preparation by windrows, which incorporate large amounts of soil and prevent complete burning of piled debris, may create soil conditions in the windrow which favor oak regeneration.

Rust-Resistant Planting Stock.  The best management tool to prevent or reduce rust losses is rust-resistant seedlings. Rust-resistant genotypes 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. Although large quantities of the best rust-resistant seed are in short supply and some rust-improved varieties are more resistant than others (no families are immune (i.e., disease free)), rust-resistant seedlings can reduce rust incidence by 20 to 80% in high-rust hazard areas (Figure 8, Table 5), with little or no reduction in growth (see Benefits of Research below).

Due to their short supply, rust-resistant seedlings should only be used in moderate- to high-rust hazard areas. Because most rust-improved seedlings currently available are from an open-pollinated, maternal, parent tree (only the mother tree is of known resistance), not all seedlings in the family are resistant. Nevertheless, a higher percentage of seedlings from rust-improved families would be rust resistant. At present, there is no standard rating at nurseries which reports the degree of disease resistance for rust-improved seedlings. Not all "genetically improved" seedlings have rust resistance; some are only improved for growth. These seedlings would not be appropriate to plant in high-rust hazard locations.
 
 
Table 5. Fifth year fusiform rust incidence on susceptible and resistant loblolly and slash pine and reduction in rust incidence due to planting rust-resistant families in operational plantations in high-rust incidence areas. (Adapted from Schmidt et al. 1985) 
Rust incidence (%) 
Location  Species  Rust susceptibility  No. of plantations  Acres  Mean  Reduction 
FL  Slash  Susceptible  88  6070  49.1  58.2 
Resistant  22  1569  20.5 
Loblolly  Susceptible  14  765  35.6  69.1 
Resistant  24  1447  11.0 
GA  Loblolly  Susceptible  82  4133  31.4  52.2 
Resistant  46  5330  15.0 
GA  Loblolly  Susceptible  71  4116  44.4  72.1 
Resistant  61  9770  12.4 
Summary  Susceptible  255  15084  Ave. 40.1  Ave. 63.0 
Resistant  153  18116  Ave. 14.7 

Plant Healthy Seedlings. In most nurseries (especially those in high-rust hazard areas) fusiform rust is effectively controlled with the systemic chemical Bayleton®. Bayleton®, applied as a seed treatment and/or sprayed on seedlings, is systemic, (i.e., it is absorbed and translocated within the seedling, protecting actively growing susceptible tissues). Since the chemical is in the seedling, it is not eroded by rain or irrigation. Bayleton® not only prevents infection, but is reported to eradicate newly established infections. Bayleton® applied in the nursery may have some residual effect immediately after outplanting, but will not long protect newly planted seedlings in the field. Bayleton® applied to seedlings and small trees (1 to 3 years) in the field has been reported to provide rust protection. However, it is difficult to protect trees beyond 3 to 5 years of age with chemical sprays applied from the ground because of the expenses and difficult logistics of application. Currently 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. In addition to reducing hardwood competition, spores which infect pine come from infected oak and reduction of oak should reduce rust incidence. However, because spores are wind-disseminated over great distances (perhaps ½ to 1 mile), there is no assurance that removing oaks from a plantation and immediate surrounding area will significantly reduce rust incidence if spores come from adjacent oak, beyond the oak removal zone. Thus, reducing oaks solely for the purpose of reducing rust incidence may not be effective. Prescribed fire and herbicides can provide effective oak control in established stands. However, if resinous stem galls on pine are ignited, trees may be killed and charring may degrade wood for some uses.

Delay 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 and early growth or in management systems for longer, solid wood rotations, delaying fertilization may be appropriate.

Alternative Species and Silviculture. 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. There is evidence to suggest that a shelterwood silvicultural system (natural regeneration of pines beneath an overstory of seed trees) can result in reduced rust incidence on understory regeneration, perhaps by creating unfavorable climate conditions (e.g., reduced surface moisture on understory regeneration). Additionally, prescribed fire, especially summer burns, can reduce oak abundance.
 

Preventing Rust in Low-hazard Areas

Few precautions need be taken 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 galls (Figure 9) 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).
 

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, 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. An 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).

Prune 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 silvicultural and wood quality advantages and may be economically feasible. However, because wounds can be colonized by the fungus, pruning should not occur during the season March - July when basidiospores may be present.

Sanitation/Salvage Thinnings. A sanitation/salvage thinning at mid-rotation age or beyond should remove diseased trees. This thinning practice, when done in conjunction with normal thinning operations, can improve the residual stand and utilize trees which otherwise would likely be lost to rust mortality 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.

Benefits of Research

Often the realized monetary benefits which accrue to the expenditure of dollars to support research are difficult to assess and poorly documented. Recently the U.S.D.A. Forest Service, using Forest Inventory and Analysis and data from several state and federal research projects, completed a benefit/cost analysis of dollars spent on fusiform rust research in the South. While the report focuses on the development and deployment of rust- resistant slash and loblolly pine seedlings, this critical aspect of reducing losses to fusiform rust would not have been possible without associated research in other areas of rust biology and ecology.

The successful development of rust resistance in southern pines began in the early 1950s and continues today ­ pointing out the significance of longterm research in forestry. A further hallmark of this successful effort has been the cooperation among scientists from state and federal laboratories, universities and industry. Again, while the focus is on pathologists and geneticists working together, many other disciplines have made significant contributions.

Information (Table 6) adapted from the U.S.D.A. Forest Service report Positive Returns from Investments in Fusiform Rust Research indicates that for every dollar spent on rust research a return of 6 to 20 dollars was realized, depending on product utilization and optimum deployment of rust-resistant seedlings. The net present value (PV) varies from approximately 245 to 949 million dollars. Among all options considered, B/C ranged from 2.2 - 20.4 and PV ranged from 59 - 949 million dollars. These figures represent an annual gain of 5-20 million dollars overall in the South.
 
 
Table 6. Benefit/cost ratio (B/C) and net present value (PV) from investments in fusiform rust research in slash and loblolly pine (adapted from Pye et al. 1997). 
Utilization 1  Benefit 
measure 2 		 Optim deployment 3 
Poor  B/C  20.4 
PV  949.7 
Pulpwood  B/C  14.1 
PV  638.2 
Sawtimber  B/C  6.9 
PV  287.9 
Full  B/C  6.0 
PV  245.0 
1 Assume a fixed 35-year rotation: poor , any tree with a stem gall is left in woods; pulpwood , any tree with a stem gall is pulped; sawtimber , infected tree pulped unless a 16 ft sawlog section is free of stem gall; full, optimum product utilization of all trees, including trees with rust galls.

2 B/C, benefit/cost ratio; PV, net present value in millions of constant 1992 dollars.

3 Optim deployment, rust-resistant seedlings were deployed in high-rust hazard areas where benefits would be greatest.

Summary

Intensively managed plantations of slash and loblolly pines are severely damaged by fusiform rust in extensive areas throughout the South and significant financial losses occur. This report summarizes important aspects of the biology, ecology and management of this disease which can severely limit the productivity of southern pine forests, including those in Florida. The critical environmental factors which affect rust incidence and spread are discussed, including the significant role of man, both in creating and solving the problem. Potential rust incidence, rust-associated mortality and volume losses are estimated. Criteria for rust-hazard risk evaluations are provided inorder to consider effective rust management, which is discussed in some detail. The important role of the successful development and deployment of rust-resistant seedlings is emphasized. Finally, the beneficial and extremely cost-effective role of regional, longterm fusiform rust research is discussed.

References

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Anderson, R.L., R.A. Schmidt, and G.A. Snow. 1984. Integrated pest management in regeneration - early growth phase of pine stands - diseases. Pages 45-71 in : S.J. Branham and G.D. Hertel, eds. Proc. Integrat. For. Pest Manage. Symp. Athens, GA. 281 p.

Belanger, R.P., T. Miller, R.A. Schmidt, and J.E. Allen. 1995. Relation of mechanical site preparation to oak abundance, pine growth, and fusiform rust incidence in a slash pine plantation. Interim Res. Rept. 34, Integrat. For. Pest Manage. Coop., Sch. For. Resourc. Conserv., Univ. Fla., Gainesville. 12 p.

Dinus, R.J. 1974. Knowledge about natural ecosystems as a guide to disease control in managed forests. Pages 184-190. in : Proc. Amer. Phytopathol. Soc. Vancouver, B.C.

Dinus, R.J. and R.A. Schmidt, eds. 1977. Management of fusiform rust in southern pines. Symp. Proc., Univ. Fla., Gainesville. 163 p.

Dwinell, L.D. 1974. Susceptibility of southern oaks to Cronartium fusiforme and Cronartium quercuum . Phytopathology 64:400-403.

Dwinell, L.D. and H.R. Powers, Jr. 1974. Potential for southern fusiform rust on western pines and oaks. Plant Dis. Rept. 58: 497-500.

Goddard, R.E. and O.O. Wells. 1977. Susceptibility of southern pines to fusiform rust. Pages 52-58 in: R.J. Dinus and R.A. Schmidt, eds. Management offusiform rust in southern pines. Symp. Proc. Univ. Fla., Gainesville. 163 p.

Griggs, M.M. and R.A. Schmidt. 1977. Increase and spread of fusiform rust. Pages 32-38 in: R.J. Dinus and R.A. Schmidt, eds. Management of fusiform rust in southern pines. Symp. Proc. Univ. Fla., Gainesville. 163 p.

Hedgcock, G.G. and P.V. Siggers. 1949. A comparison of pine-oak rusts. U.S. Dept. Agric. Tech. Bull. 978. 30 p.

Kelley, W.D. and G.B. Runion. 1991. Control of fusiform rust on loblolly and slash pine seedlings in forest nurseries in the southeastern United States. Pages 338-340 in : Y. Hiratsuka, J.K. Samoil, P.V. Blenis, P.E. Crane and B.L. Laishley, eds. Rusts of pine. Proc. Internl. Union For. Res. Org. Work. Party Conf., Banff, Alberta, Can. Info. Rept. NOR-X-317. 408 p.

Nance, W.L., R.D. Froelich, T.R. Dell, and E. Shoulders. 1982. A growth and yield model for unthinned slash pine plantations infected with fusiform rust. Pages 275-282 in E.P. Jones, Jr., ed., Proc. 2 nd Biennial So. Silvicul. Res. Conf. Atlanta, Ga. 514 p.

Powers, H.R., Jr. 1975. Relative susceptibility of five southern pines to Cronartium quercuum . Plant Dis. Rept. 59:312-314.

Powers, H.R., Jr., J.P. McClure, H.A.Knight, and G.F. Dutrow. 1975. Fusiform rust: forest survey incidence data and financial impact in the south. U.S. Dept. Agric. For. Serv., Southeast. For. Exp. Stn. Res. Pap. SE-127. 16 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.

Pye, J.M., J.E. Wagner, T.P. Holmes, and F. W. Cubbage. 1997. Positive returns from investment in fusiform rust research. Res. Pap. SRS-4. Asheville, NC. U.S. Dept. Agric. For. Serv. South. Res. Stn. 55 p.

Rowan, S.J., W.H. McNab, and E.V. Brender. 1975. Pine overstory reduces fusiform rust in underplanted loblolly pine. U.S. Dept. Agric. For. Serv. Res. Note SE-212.60, 6 p.

Schmidt, R.A. 1978. Diseases in forest ecosystems: the importance of functional diversity. Pages 287-315 in: J.G. Horsfall and E.B. Cowling, eds. Plant Disease: An Advanced Treatise. Vol. II. How disease develops in populations. Acad. Press., New York. 436 p.

Schmidt, R.A. and J.E. Allen. 1991. Temporal and spatial variation affecting fusiform rust hazard prediction in slash pine plantations in the southeastern United States. 1991, Pages 139-148.in:Y. Hiratuska, J.K. Samoil, P.V. Blenis, P.E. Crane, and B.L. Laishley, eds . Proc. Internl. Union For. Res. Org. Work. Party Conf. Rusts of pine ,. Banff, Alberta, Canada. Info. Rept. NOR-X-317.408p:

Schmidt, R.A. and J.E. Allen. 1995. Geographic variation in fusiform rust incidence on progeny of open-pollinated resistant and susceptible slash pine families in the Coastal Plain. Integrat. For. Pest Manage. Coop., Interim Res. Rept. 35. Sch. For. Resourc. Conserv., Univ. Fla. Gainesville. 44 p.

Schmidt, R.A., J.E. Allen, R.P. Belanger, and T. Miller. 1995. Influence of oak control and pine growth on fusiform rust incidence in young slash and loblolly pine plantations. South. J. Appl. For. 19:151-156.

Schmidt. R.A., R.C. Holley, and M.C. Klapproth. 1985. Results from operational plantings of fusiform rust resistant slash and loblolly pines in high rust incidence areas in Florida and Georgia. Pages 33-41 in: J. Barrows-Broaddus and H.R. Powers, Jr., eds. Proc. Internl. Union For. Res. Org. Rust of hard pines Work. Party Conf. S2-06-10. Athens, GA. 331 p.

Schmidt, R.A., E. J. Jokela, J.E. Allen, R.P. Belanger, and T. Miller. 1990. Association between fusiform rust incidence and CRIFF soil classification for slash pine plantations in the Coastal Plain of Florida and Georgia. South. J. Appl. For. 14:39-43.

Schmidt, R.A. and M.C. Klapproth. 1982. Delineation of fusiform rust hazard based on estimated volume loss as a guide to rust management decisions in slash pine plantations. South. J. Appl. For. 6:59-63.

Schmidt. R.A., H.R. Powers, Jr., and G.A. Snow. 1981. Application of genetic disease resistance for the control of fusiform rust in intensively managed southern pine. Phytopathology 71:993-997.

Schmidt, R.A. and D. Wilson. 1997. Geographic variation in fusiform rust incidence on progeny of resistant and susceptible slash pine families in the Coastal Plain: rust virulence study - third planting established in 1991. For. Biology Res. Coop., Sch. For. Resourc. Conserv., Univ. Fla. Gainesville. 36 p.

Starkey, D.A., R.L. Anderson, C.H. Young, N.D. Cost, J.S. Vissaage, D.M. May, and E. K. Yockey. 1997. Monitoring incidence of fusiform rust in the South and change over time. U.S. Dept. Agric. For. Serv., South. Region For. Health Prot. Rept. R8-PR30. 29 p.

Acknowledgments

Many scientists from state, federal and industry laboratories have contributed to the information contained herein and I have attempted to show appropriate credit both in the tables and figures, and in the literature references. Much of the information comes from the research programs of School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida, both published and unpublished, as noted. In many instances, the forest industry played a major role through their participation in the Integrated Forest Pest Management Cooperative, the Cooperative Forest Genetics Research Program and the Cooperative Research in Forest Tree Fertilization in the School of Forest Resources and Conservation.

1 . The Cooperative Research in Forest Fertilization (CRIFF) program at the School of Forest Resources and Conservation, University of Florida, has defined eight soil types (A-H) which are widely used in forest soil management, especially with respect to fertilization. Type E and F are moderately-well to well-drained soils lacking a spodic horizon and having an argillic (clay) layer at depths of approximately 10-50 inches.

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