United States

Department of

Agriculture

Forest Service

An Integrated Approach Toward

Reducing Losses from Fusiform Rust

in Merchantable Slash and Loblolly

Pine Plantations

Southern

Research Station

Research Paper

SRS-23

Roger P. Belanger, Thomas Miller, Stanley J. Zarnoch,

Stephen W. Fraedrich, and John F. Godbee
The Authors

Roger I? Belanger was a Principal Silviculturist (now retired) and Thomas

Miller was a Principal Plant Pathologist (now retired) at the Southern

Research Station, U.S. Department of Agriculture, Forest Service,

University of Florida, Gainesville, FL 32611. Stanley J. Zarnoch is a

Mathematical Statistician at the Southern Research Station, U.S.

Department of Agriculture, Forest Service, PO. Box 2680, Asheville, NC

28802. Stephen W. Fraedrich is a Plant Pathologist at the Southern

Research Station, U.S. Department of Agriculture, Forest Service, 320

Green Street, Athens, GA 30602; ,and John F. Godbee is the Environmental

Affairs Manager at the International Paper Company, P.O. Box 1391,

Savannah, GA 3 1402.

December 2000

Southern Research Station

P.O. Box 2680

Asheville, NC 28802
An Integrated Approach Toward Reducing

Losses from Fusiform Rust in Merchantable

Slash and Loblolly Pine Plantations

Roger P. Belanger, Thomas Miller, Stanley J. Zarnoch,

Stephen W. Fraedrich, and John F. Godbee

Abstract

The primary objective of this study was to evaluate the selective

thinning of trees with rust galls as a means of reducing losses to the

fusiform rust (Cronurtium yuercuum (Berk.) Miyabe ex Shirai f. sp.

fusiforme) disease in merchantable slash (Pinus elliottiiEngelm. var.

elliortii)and loblolly (P taeda L.) pine plantations. Additional

objectives were to assess the post-thinning occurrence and impacts of

southern pine beetles (Dendroctonus frontalisZimm.) and annosum

root rot (Heterobasidion anno~um Fr.). Nineteen rust-infected

plantations were selected in Alabama, Georgia, and South Carolina to

represent a wide range of stand and rust conditions. Thinnings were

based primarily on the removal of trees with severe and moderate

stem girdling caused by fusiform rust galls. Approximately 750 acres

were thinned operationally to salvage potential mortality; 2,250

nonthinned acres served as controls. Study plots were surveyed

annually for IO years to determine the amount and causes of

mortality. Stand growth and development were evaluated at the end of

5- and IO-year periods after treatment. Removal of rust-infected

stems greatly improved the quality of trees in the residual stands. The

periodic diameter growth of individual dominant and codominant slash

and loblolly pine trees was affected by the extent of stem girdling.

Trees with severe stem girdling (250 percent) grew significantly less

than gall-free trees or trees with small or moderate stem girdling.

Trends in periodic stand growth and total volume production were

similar for slash and loblolly pine. Standing volume at the end of IO

years was greater in nonthinned portions of the plantations than in

thinned portions. However, periodic stand growth and ingrowth of

rust-free sawtimber (29 inches in diameter at breast height) were

greater in thinned portions of the plantation. Rust-associated

mortality was the primary factor that reduced volume growth and

production in slash pine plantations. Losses from fusiform rust and

the southern pine beetle had a severe impact on total production in

the loblolly plantations. Thinning significantly reduced losses from

both of these forest pests. Management implications can be

‘incorporated into conventional thinning procedures for regulating

stand density, increasing growth, and improving stand health.

Keywords: Annosum root rot, forest health, integrated pest

management, Pinus elliottii Engelm. var. elliorrii, Pinus taeda L.

southern pine beetle, thinning.

Introduction

There are over 25 million acres of pine plantations in the

Southern United States. Recent assessments indicate the

total area in pine plantations will more than double by the

year 2030 (U.S. Department of Agriculture 1988). Slash pine

(Pinus elliottii Engelm. var. elliortii) and loblolly pine (c!

rueda L.) are the species planted most commonly in the

South. These two species are also the most susceptible to

damage caused by fusiform rust (Cronartium quercuum

(Berk.) Miyabe ex Shirai f. sp.fusiforme). Recent surveys

show that slash and loblolly pine plots with > 10 percent rust

incidence are distributed over nearly the entire range of each

species (Starkey and others 1997). Losses to fusiform rust

result from mortality, stem defect, and a reduction in the

growth of trees with severe stem galls. A high incidence of

rust in pine plantations severely limits management options

and objectives.

Significant advances have been made during the past 20

years in the development of management strategies to

reduce losses from fusiform rust. Methods have been

developed for predicting the relative rust hazard of sites for

both slash and loblolly pines (Anderson and others 1986,

Borders and Bailey 1986, Froelich and Snow 1986, Starkey

and others 1997). Rust resistant planting stock is available

for use in high-rust hazard areas (Powers and Kraus 1986,

Schmidt and others 1981). Models provide the opportunity

for assessing the combined effects of site quality, stand

density, age, and level of fusiform rust infection on future

yields of infected slash and loblolly pine plantations (Nance

and others 1983,1985). These models emphasize the

importance of preventing rust during stand establishment

(O-5 years), when the potential impact of rust infection is the

greatest.

Forest surveys, completed at about the time this study was

initiated, indicate that more than 50 percent of the slash and

loblolly pine plantations-approximately 15 million acreswere greater than 10 years of age (Sheffield and Knight 1982,

Sheffield and others 1983, U.S. Department of Agriculture

1988). Many plantations, especially those located in highhazard rust areas, continue to be heavily infected with

fusiform rust (Starkey and others 1997). The selective

thinning of trees with severe stem galls has been proposed

as a means of reducing losses to rust in merchantable pine

plantations (Malac 1978, Powers and others 1974). Yet, little

is known about the value, practicality, and response of

stands subjected to thinning based on the incidence and

severity of fusiform rust. In 198 1, several members of the
newly-formed Integrated Forest Pest Management

Cooperative requested a research study to determine

whether or not merchantable-aged plantations of slash and

loblolly pines with moderate to high incidences of fusiform

rust could or should be treated. From 198 1 to 1992, a 1 O-year

study was conducted in Alabama, Georgia, and South

Carolina to better understand and manage fusiform rust in

merchantable slash and loblolly pine plantations.

Silvicultural options, pest management principles, and

operational practices were integrated to meet the following

objectives:

Assess improvements in stand quality after thinning;

Quantify mortality caused by fusiform rust, the southern

pine beetle (Dendroctonusfrontalis Zimm.) (SPB), and

annosum root rot (Heterobasidion annosum Fr.) over the

IO-year study period;

Determine whether severity of stem girdling by fusiform

rust affects the periodic diameter growth of individual

trees;

Evaluate periodic volume growth and total yield in

thinned and nonthinned plantations;

Compare differences in treatment responses between

slash and loblolly pine;

Assess advantages and disadvantages of selective

thinning in rust-infected plantations; and

Develop management recommendations for assessing

and reducing losses from fusiform rust in merchantable

slash and loblolly pine plantations.

Study Plantations and Methods

A long-term cooperative study was established in the early

1980’s to determine the biological responses and cultural

options associated with thinning stands infected with

fusiform rust (Belanger and others 1985, Miller and others

1985). Study plantations were selected to represent a wide

range of stand and rust conditions.

Ten slash pine plantations were located in the Coastal Plain

of Georgia and South Carolina-3 in Georgia and 7 in South

Carolina. Nine loblolly pine plantations were located in the

Coastal Plain of Georgia and Alabama-two in Georgia and

seven in Alabama. Plantation size ranged from 50 to 200

acres. Four l/4-acre permanent plots were established in

randomly designated thinned and nonthinned portions of

each plantation (randomized block design). All trees in the

l/4-acre plots were numbered to maintain their identities

throughout the study. Diameter at breast height (d.b.h.),

number of stem and branch galls, crown class, and a risk

class based on rust severity were recorded for each tree. The

fifth tree in each diameter class was selected to record

detailed rust characteristics and tree heights. The stem gall

characteristics measured and recorded in this 20-percent

subsample were (1) the height aboveground, (2) the

estimated percentage of stem circumference affected by each

gall, and (3) the estimated proportion of each rust gall with

sunken areas usually containing areas of decay, insect

activity, or both that are referred to as cankers. Tree heights

were measured to determine site index and develop volume

equations for individual plantations.

Guidelines for lkee Removal

The success of selective thinning in rust-infected

plantations is based on anticipated mortality. The following

criteria-based on rust severity-were used to mark and

remove trees with stem infections:

High risk: trees likely to die before rotation: number of stem

galls 22, stem girdling 250 percent by at least one gall;

Moderate risk: tree survival to rotation age questionable:

number of stem galls = 1, stem girdling 250 percent;

Low risk: trees likely to survive through rotation: stem

girdling ~50 percent.

The proportion of gall cankering was not used in the final

rust severity index because obtaining an objective

assessment of the extent of cankering is difficult.

Most high-risk trees were marked for removal; low-risk trees

were not marked. Moderate-risk trees provided flexibility in

the selection process; their removal was based on the

potential value of individual trees, spacing within the stand,

and yield requirements for thinning. Trees were cut and

removed throughout the year. Scheduling was strongly

dependent on the availability of logging crews, weather, and

local demands for pulpwood. Cutting to provide access

rows for logging equipment removed trees from all diameter

and risk classes.

Assessing Pest Damage and Treatment Differences

Study plots were surveyed annually to determine amount

and causes of mortality. Rust-associated mortality (RAM)

was defined as any dead tree with a stem gall and included

stem-breakage if the break occurred at a gall. Additional

mortality was attributed to SPB and a category classified as

other (e.g., root diseases, climatic effects, logging, fire,

cutting for access roads, other insects).

L
Annosum root rot hazard ratings were determined for

plantations based on soil types. During the seventh growing

season, a total of 3,832 roots were sampled from thinned and

nonthinned plots. These roots were washed, scraped, and

examined for symptoms of root diseases. A sub-sample (12

percent) of symptomatic roots was cultured in the laboratory

to determine the occurrence of H. annosum in damaged

tissue.

The d.b.h. of all trees in the thinned and nonthinned

portions of the study plantations was remeasured at 5-year

intervals to evaluate the effects of treatment, fusiform rust,

and other pests on individual tree growth, stand growth and

development, and total yield over a lo-year period. To

reduce the confounding effect of crown position on

individual tree growth, only dominant and codominant trees

were used to assess the influence of treatment, rust

occurrence, and risk class on periodic diameter growth.

Periodic yields were estimated using local volume tables

developed for individual plantations. Analyses of variance

were used to compare thinning and nonthinning treatments

and to separate the influence of rust severity on tree growth.

Significant differences between means were tested at the

0.05 probability level.

Results-Slash Pine

Stand and rust characteristics-Ages of the 10 slash pine

plantations averaged 16 years when the study was

established and ranged from 13 to 21 years. Average site

quality at 25 years was 62 (Bennett and others 1959). Study

plots contained an average of 437 live trees per acre and an

average total volume (Bennett and others 1959) of 2,398

cubic feet (ft”) per acre. Average d.b.h. was 6.1 inches (in.).

Approximately 9 percent of the stems were sawtimber-sized

trees (d.b.h. 29.0 in.). Susceptibility of the sites to H.

annosum infection was ranked as intermediate to low for

eight plantations. Hazard rankings for the other two

plantations were intermediate and high.

The slash pine study plots contained an average of 207

infected stems per acre. Incidence of stem infections

averaged 47 percent and ranged from 35 to 70 percent. The

average stem gall girdled 63 percent of the stem

circumference. Forty-six percent of infected stems was

classified as high-risk trees.

Southern pine beetle activity was endemic in the Atlantic

Coastal Plain when the study was initiated. Beetle-caused

mortality was not evident in the slash pine plantations

before or immediately after thinning operations.

Immediate Mums-ma@blssalvaged-Table 1 shows

average stand and individual tree characteristics after the

selective thinning of rust-infected stems. Most of the trees

removed (85 percent) were from the high- and moderate-risl

rust classes. High-risk trees represented approximately 46

percent of the total slash pine volume harvested. High-risk

trees that were not cut were generally too small for efficien

and effective harvest.

Rust profiles developed for high-, moderate-, and low-risk

trees indicate infections were equally and proportionally

distributed over all diameter classes. Because rust severity

Table l-Average stand structure and individual tree characteristics after the selective thinning

of fusiform rust-infected stems in 10 slash pine plantations in the Coastal Plain of Georgia and

South Carolina

Treatment Basal area

Stand structure Tree characteristics

Volume Live trees D.b.h. Height

FtVacre

Thinned

Initial 97

Removed 30

Residual 67

Nonthinned 95

-

D.b.h. = diameter at breast height.

FtVacre No./acre

2,403 437

731 141

1,672 2 %

2,391 308

In. Ft

6.1 47.2

5.9 46.5

6.2 47.5

6.4 47.8
was the primary basis for marking and removal, thinning did

not significantly change the average diameter, average tree

height, or diameter distribution of slash pine.

Improvement in stand quality-The average number of rustinfected stems, rust incidence, total number of stem galls,

and severity of rust infection was high in the slash pine

plantations before thinning (table 2). Thinning removed 77

percent of the high-risk trees. Thinning reduced incidence of

stem galls by 22 percent, total number of stem galls by 70

percent, and average gall severity by 15 percent. Residual

stem galls were small and had little cankering.

Periodic responses-mortality--Total mortality during the

lo-year study period was significantly higher in nonthinned

portions of slash pine plantations than in thinned portions

(table 3). Rust-associated mortality accounted for 78 percent

of the total volume losses in nonthinned areas. Most of the

remaining mortality was attributed to other causes and

factors that could not be identified. High-risk trees

accounted for 65 percent of total RAM.

Net differences in total volume losses between thinned and

nonthinned plots averaged 329 ft3 per acre. This equates to

an annual gain of approximately 0.35 cords of wood per acre.

The major portion (91 percent) of this volume gain resulted

from the salvage removal of rust-infected trees. The average

d.b.h. and total height of trees killed by SPB attack were

greater than those of trees killed by fusiform rust (table 4).

Much of the remaining mortality in the thinned plots

occurred in small trees that sustained mechanical injury

during thinning operations. Other mortality in nonthinned

Table 2-Average fusiform rust characteristics after the selective thinning of rust-infected stems in

10 slash pine plantations in the Coastal Plain of Georgia and South Carolina

Treatment

Infected

stems

Stem infections

Total stem

Incidence galls

High risk

trees

Gall characteristics

Circumference” Max.h

Thinned

Initial

Removed

Residual

Nonthinned

No/acre Percent ------No./acre------ _ _ _ _ _ _ percent _ _ _ _ _ _

207 47 372 96 6 3 71

13Z! 94 258 74 72 82

75 2 5 114 22 4 8 52

191 48 339 110 6 3 7 1

I’ Average percentage of stem circumference girdled.

b Percentage of stem circumference girdled by most severe gall.

Table 3-Average lo-year mortality and volume losses caused by fusiform rust, the southern pine

beetle, and other factors in thinned and nonthinued portions of 10 slash pine plantations in the

Coastal Plain of Georgia and South Carolina

Cause

Thinned Nonthinned

Tree mortality Volume loss Tree mortality Volume loss

Nolucre Ft3/acre No/acre Ft3/acre

Fusiform rust 17.8 74.3 73.7 373.7

SPB 1.6 7.8 5.4 28.6

Other and unknown 22.8 66.2 24.1 74.8

Total 42.2 148.3 103.2 477.1

SPB = Southern pine beetle.
Table 4-Average diameter at breast height and total height of trees killed by fusiform rust,

the southern pine beetle, and other factors in thinned and nonthinned portions of 10 slash

pine plantations in the Coastal Plain of Georgia and South Carolina

Cause

Fusiform rust

SPB

Other and unknown

Thinned Nonthinned

D.b.h. Height D.b.h. Height

In. Ft In. Ft

5.2 42.4 5.8 46.4

5.6 46.4 6.1 48.1

4.3 39.7 4.3 39.8

D.b.h. = diameter at breast height; SPB = southern pine beetle.

plots was mostly in intermediate and suppressed trees in disturbance were associated with any of the SPB outbreaks

gradual decline from crown competition. in slash pine plantations.

Accumulative annual tree mortality and associated volume

losses caused by fusiform rust were low during the 2 years

immediately after thinning but increased at a relatively

constant rate during years 3 through 10 (figs. 1,2). This trend

was particularly evident in the nonthinned plots. , ,

Losses attributed to SPB attack and spot spread were

minimal during the IO-year study period. No visible signs of

90-

60-

-2

Y 70-

a

ims

rh50- 1

e

2 40-

%

1 30-

Iu ma

10 -

4- NonthInned rut

+ lllinnedmst

4 NonthInned SPB

4 ThllmedSPB

0

1 2 3 4 5 6 7 6 9 10

Years after thinning

Figure l-Accumulative tree mortality caused by fusiform rust and the

southern pine beetle (SPB) in thinned and nonthinned portions of 10

slash pine plantations in the Coastal Plain of Georgia and South

Carolina.

Symptoms of root diseases were evident in approximately 16

percent of the roots sampled (table 5). There were no

significant statistical differences between the percentages of

symptomatic slash pine roots from thinned and nonthinned

areas. The annosum rust rot fungus was isolated from less

than 1 percent of the symptomatic roots (table 6). No

mortality in thinned or nonthinned plots was attributed to

root decay fungi.

--A- NonthInned rust

+ ThinnF.dmst

-o- NonthInned SPB

4 ThlmedSPB

I 2 3 4 5 6 7 8 9 10

Years after thinning

Figure 2-Accumulative volume loss caused by fusiform rust and the

southern pine beetle (SPB) in thinned and nonthinned portions of IO

slash pine plantations in the Coastal Plain of Georgia and South

Carolina.

5
Table 5-The incidence of roots with symptoms typical of

Heterobusidion annosum in thinned and nonthinned

portions of 10 slash pine plantations in the Coastal Plain of

Georgia and South Carolina

Treatment Sampled Symptoms

Thinned 972 145 (14.9)4

Nonthinned 1,024 173 (17.9)

Total 1,996 318 (15.9)

” Percent of infected roots.

Table 6-The incidence of Heterobasidion annosum

isolated from symptomatic roots sampled from thiied and

nonthinned portions of 10 slash pine plantations in the

Coastal Plain of Georgia and South Carolina

Treatment

Symptomatic

roots sampled

Infected

rootsa

Thinned

Nonthinned

91 1 (l.l)b

120 0 (0.0)

Total 211 1 (0.5)

n Based on laboratory cultures from symptomatic roots.

b Percent of infected roots.

Periodic diameter growth-When the study was initiated,

there were no significant differences in the average d.b.h. of

residual dominant and codominant slash pine trees between

thinned and nonthinned plots or between rust-free and rustinfected trees (table 7). Average diameter growth over the loyear study period was also nonsignificant between thinned

and nonthinned plots and between rust-infected and rustfree trees. Differences in periodic growth were significant,

however, between risk classes. Diameter growth of trees with

multiple galls and severe girdling was significantly less than

moderate-risk, low-risk, or rust-free trees. Growth losses and

related mortality associated with high-risk trees were

significant during both 5-year measurement periods.

Periodic stand growth and total yield-Treatment, total

mortality, and fusiform rust affected the average periodic

growth and total yield of the slash pine plantations. After 10

years, average basal area, volume, and number of live trees

per acre were greater in nonthinned plots than in thinned

plots (table 8). However, periodic basal area growth and

volume growth during the 1 O-year period were significantly

Table ‘I--Average diameter at breast height and periodic

growth of dominant and codominant slash pine trees as

affected by treatment, rust incidence, and risk class in 10

slash pine plantations in the Coastal Plain of Georgia and

South Carolina

Diameter at breast height

Variable Initial

Total

5 years 10 years difference

Treatment

Thinned

Nonthinned

Rust occurrence

Rust galls

Rust-free

7.0 8.1 9.2 2.2

7.4 8.5 9.4 2.0

7.3 8.3 9.3 2.0

7.2 8.2 9.3 2.1

Risk class

Rust-free

Low

Moderate

High

7.2 8.2 9.3 2.1

7.3 8.4 9.5 2.2

7.6 8.6 9.6 2.0

7.0 7.7 8.4 1.4”

a Significantly different at 0.05 probability level.

greater in thinned plots than in nonthinned plots. Average

total yield (thinned volume added to standing live volume)

was also significantly greater for thinned plots (3,460 ft3 per

acre) than for nonthinned plots (3,193 ft3 per acre). Mortality

accounted for most of the differences in periodic growth.

Losses in nonthinned plots were mostly rust associated and

evenly distributed across diameter classes. Losses in

thinned plots were mostly small trees damaged during

logging operations. The selective cutting of high-risk trees

reduced the potential for mortality in thinned plots.

At the end of the I O-year study period, the average number

of sawtimber-sized trees per acre was marginally greater in

nonthinned plots than thinned plots. However, 80 trees (75

percent) in the thinned plots were rust-free, 26 trees (24

percent) were in the low- or moderate-risk classes, and only 1

tree had severe stem girdling (table 8). By comparison, in the

nonthinned plots, only 59 trees (48 percent) were rust-free,

55 trees (44 percent) were low- or moderate-risk trees, and 10

trees had severe stem girdling. Although rate of ingrowth

was similar for both treatments, thinning improved the

quality of high-value, sawtimber-sized trees significantly.

6

.^.
Table g-Average periodic growth in thinned and nonthinned portions of 10 slash pine

plantations after the selective thinning of rust-infected stems in the Coastal Plain of

Georgia and South Carolina

Treatment Basal area

Ft2/acre

Thinned

Initial 67

5 years 84

10 years 104

Difference 37

Nonthinned

Initial 95

5 years 107

10 years 121

Difference 26

n Trees Z 9.0 in. diameter at breast height.

Stand structure

Volume Live trees

Ftj/acre NoJacre

1,672 296

2,241 270

2,729 252

1,057 -44

2,391 398

2,886 337

3,193 288

802 -110

Sawtimber a

No/acre

21

54

107

86

24

70

124

100

Results-Loblolly Pine

Stand and rust characteristics-Average age of the nine

loblolly pine plantations was 17 years when the study was

established and ranged from 16 to 22 years. Average site

quality at 25 years was 70 (Clutter and Lenhart 1968). Study

plots contained an average of 462 trees per acre and a total

volume (Bailey and Clutter 1970) of 2,856 ft3 per acre.

Average d.b.h. was 6.8 inches. Approximately 16 percent of

the stems were sawtimber-sized trees. Risk analysis ranked

the potential for II annosum infection as intermediate or low

for seven of the plantation sites. The remaining two

plantations were ranked as intermediate- to high-hazard

sites.

The loblolly pine plots contained an average of 268 infected

stems per acre. Incidence of stem galls averaged 58 percent

and ranged from 46 to 74 percent. The average stem gall

girdled 52 percent of the stem circumferences. Thirty-three

percent of the infected stems were classified as high-risk

trees.

Southern pine beetle populations were endemic in the

Atlantic Gulf Coastal Plain when the study was initiated.

There was no evidence of beetle-caused mortality in the

loblolly pine study plantations before or immediately after

thinning operations.

Immediate returns-materials salvaged-Extent of thinning

in the nine loblolly pine plantations was generally classified

as light to moderate (table 9). Average basal area was

reduced from 126 to 97 ft* per acre. Residual stocking in the

thinned stands averaged 333 live stems per acre. As with

slash pine, thinning did not significantly change the average

diameter, average tree height, or diameter distribution of

loblolly pine.

Improvement in stand quality-Selective thinning reduced

the number and severity of infected stems in the loblolly

pine plantations (table 10). Incidence of stem infections was

reduced from 59 to 47 percent with the total number of stem

infections reduced by 49 percent. Thinning removed 71

percent of all high-risk trees. The average amount of stem

circumference girdled was reduced from 5 1 to 42 percent.

Periodic responses-mortality-Toy-Total mortality in the

nonthinned portions of the loblolly pine plantations was

significantly higher than that recorded in thinned plantations

during the lo-year measurement period (table 11). Rustassociated mortality accounted for 5 1 percent of the total

volume loss. High-risk trees accounted for 65 percent of total

RAM. Mortality classified as other and unknown accounted

for only 11 percent of the total volume loss. Most of these

losses were attributed to the gradual suppression of small

trees (table 12).
Table 9-Average stand structure and individual tree characteristics after the selective thinning

of fusiform rust-infected stems in nine loblolly pine plantations in the Coastal Plain of Alabama

andGeorgia

Treatment Basal area

Stand structure

Volume Live trees

Tree characteristics

D.b.h. Height

Ft2/acre Ft3/acre NoJacre In. Ft

Thinned

Initial 126

Removed 29

Residual 97

Nonthinned 122

I>.b.h. = diameter at breast height.

2,910 460 6.9 49.5

633 127 6.4 47.8

2,277 333 7.1 50.1

2,803 464 6.7 49.2

Table lO-Average fusiform rust characteristics after the selective thinning of rust-infected stems in

nine loblolly pine plantations in the Coastal Plain of Alabama and Georgia

Stem infections Gall characteristics

-

Infected Total stem High risk

Treatment stems Incidence galls trees Circumference” Max.6

No./acre Percent _ _ _ _ _ No/acre _ _ _ _ - _ _ _ _ _ _ percent- _ - - - -

Thinned

Initial

Removed

Residual

Nonthinned

272 59 4% 86 51 60

114 90 243 61 62 76

158 47 253 25 42 49

264 57 491 92 53 63

0 Average percentage of stem circumference girdled.

b Percentage of stem circumference girdled by most severe gall.

Table 11-AveragelO-year tree mortality and volume losses caused by fusiform rust, southern pine

beetle, and other factors in thinned and nonthinned portions of nine loblolly pine plantations in the

Coastal Plain of Alabama and Georgia

Cause

Thinned Nonthinned

Tree mortality Volume loss Tree mortality Volume loss

No/acre Ft3/acre No/acre Ft3/acre

Fusiform rust 30.6 139.4 90.3 343.2

SPB 13.3 139.6 27.2 251.4

Other and unknown 22.0 85.2 28.7 74.1

Total 65.9 364.2 146.2 668.7

SPB = Southern pine beetle.

8

-.
Table U-Average diameter at breast height and total height of trees killed by fusiform rust,

southern pine beetle, and other factors in thinned and nonthinned portions of nine loblolly

pine plantations in the Coastal Plain of Alabama and Georgia

Cause

Fusiform rust

SPB

Other and unknown

Thinned Nonthinned

D.b.h. Height D.b.h. Height

In. Ft 4 In. Ft

5.7 46.6 5.5 45.7

8.5 46.6 8.0 55.2

5.1 43.6 4.6 42.1

D.b.h. = diameter at breast height; SPB = southern pine beetle.

Net difference in total volume losses between thinned and

nonthinned study plots averaged 305 ft per acre. Differences

in rust-associated mortality between thinned and

nonthinned plots accounted for 67 percent of the total

volume salvaged by thinning. Tree mortality and volume

losses caused by fusiform rust increased at a relatively

constant rate in thinned and nonthinned study plots

throughout the IO-year period (figs. 3.4).

I 2 3 4 5 6 7 8 9 IO I 2 3 4 5 6 7 8 9 I O

Years after thinning Years after thinning

Figure 3-Accumulative tree mortality caused by fusiform rust and

the southern pine beetle (SPB) in thinned and nonthinned portions of

nine loblolly pine plantations in the Coastal Plain of Alabama and

Georgia.

Southern pine beetle attack and spot spread were significant

causes of mortality in both thinned and nonthinned

plantations (figs. 3,4). Southern pine beetle activity was low

in the Gulf Coastal Plain during the early years of the study,

increased during years 7 and 8, and became epidemic in

years 9 and IO. Total volume loss caused by the SPB was 38

percent of all losses in nonthinned plots over the IO-year

400

3 350

P

f 300

2

i 250

2

0

3

200

‘ij

* 150

z

1

‘3 100

0

e

4 50

0 7-

* NoDtbinnedrust

-+lllbnedrmt

+NoatbbllKdsPB

tTllhnedSPB

Figure 4-Accumulative volume loss caused by fusiform rust and the

southern pine beetle (SPB) in thinned and nonthinned portions of

nine loblolly pine plantations in the Coastal Plain of Alabama and

Georgia.

9
period. Total tree mortality and volume losses caused by

SPB activity were approximately twice as much in

nonthinned plots as in thinned plots. Average d.b.h. and

total height of trees killed by SPB were significantly greater

than trees killed by fusiform rust or other causes (table 12).

In thinned and nonthinned plots, losses of sawtimber

volume caused by the SPB were more than three times

greater than losses attributed to fusiform rust (fig. 5).

Like slash pine, the percentage of loblolly pine roots with

symptoms typical of H. annosum did not differ significantly

between thinned and nonthinned treatment areas (table 13).

Heterobasidion annosum was isolated from 7.1 percent of

+ NonthInned rust

- Thlnnedmat

4 NonthInned SPB

+ ‘INnnedSPB

1 2 3 4 5 6 7 8 9 10

Years after thinning

Figure 5-Accumulative sawtimber volume loss caused by fusiform rust

and the southern pine beetle (SPB) in thinned and nonthinned

portions of nine loblolly pine plantations in the Coastal Plain of

Alabama and Georgia.

Table D-The incidence of roots with symptoms typical of

Heterobasidion annosum in thinned and nonthhmed

portions of nine loblolly pine plantations in the Coastal

Plain of Alabama and Georgia

Treatment Sampled Symptoms

Thinned

Nonthinned

913 158 (17.3)

923 147 (15.9)

Total 1,836 305 (16.6)

” Percent of infected roots. a Significantly different at 0.05 probability level.

10

symptomatic loblolly roots (table 14). No mortality in thinned

or nonthinned plots was attributed to root diseases.

Periodic diameter growth-When the study was initiated,

there was no significant difference in the average d.b.h. of

residual dominant and codominant loblolly pine trees

between thinned and nonthinned plots (table 15). The

average d.b.h. and diameter growth did not differ

Table M-The incidence of Heterobasidion annosum from

symptomatic roots sampled from thhmed and nonthiied

portions of nine loblolly pine plantations in the Coastal

Plain of Alabama and Georgia

Symptomatic Infected

Treatment roots sampled root@

Thinned 140 10 (7.l)b

Nonthinned 115 8 (7.0)

Total 255 18 (7.1)

“Based on laboratory cultures from symptomatic roots.

bPercent of infected roots.

Table G-Average diameter at breast height and periodic

growth of dominant and codominant loblolly pine trees as

affected by treatment, fusiform rust occurrence, and risk

class in nine loblolly pine plantations in the Coastal Plain of

AlabamaandGeorgia

Diameter at breast height

Variable

Total

Initial 5 years 10 years difference

Treatment

Thinned 7.9 8.9

Nonthinned 7.7 8.7

Rust occurrence

Rust galls 7.7 8.7

Rust-free 7.8 8.8

9.9 2.0

9.4 1.70

9.5 I.8

9.7 1.9

Risk class

Rust-free

Low

Moderate

High

7.8 8.8 9.7 1.9

8.0 9.0 9.8 1.8

7.6 8.7 9.4 I.8

7.4 8.3 8.9 1.5a
significantly between trees in thinned and nonthinned plots

during the 5-year period after treatment. Response to

thinning did occur, however, during the 6- through 1 O-year

growth period. Final measurements showed significantly

greater d.b.h. growth for trees in thinned plots than in

nonthinned plots.

Average diameter growth over the lo-year study period

between rust-infected and rust-free trees was nonsignificant.

Like slash pine, high-risk loblolly pines grew significantly

less than those with no rust infections. There were no

significant differences in average diameter growth between

moderate-risk, low-risk, and rust-free trees. Growth losses

were closely related to high mortality rate associated with

high-risk trees. There were no significant correlations

between the number of high-risk trees or growth losses and

SPB incidence or amount of SPB-related mortality.

Periodic stand growth and total yield-After 10 years, the

average stand basal area, total standing volume, and number

of live trees per acre in the loblolly pine plantations were

greater in the nonthinned plots than thinned plots (table 16).

Periodic basal area increment and volume growth, however,

were significantly greater in thinned plots than in

nonthinned plots. Average total yield (thinned volume

added to standing live volume) was also significantly greater

in thinned plots (3,791 fC per acre) than nonthinned plots

(3,489 ft3 per acre). Large amounts of rust-associated

mortality and losses from SPB activity accounted for

substantial volume reductions in the nonthinned plots.

Final stand structure showed the average number of

sawtimber-sized trees was similar for thinned and

nonthinned plots. The notable difference between

treatments was in tree quality. In thinned plots, there was an

average of 66 rust-free trees per acre, 75 low- or moderaterisk trees, and only 1 tree per acre with severe stem girdling

caused by fusiform rust. By comparison, nonthinned plots

had an average of 57 rust-free trees per acre, 83 low- or

moderate-risk trees per acre, and 6 high-risk trees per acre.

Reductions in diameter growth caused by severe stem

girdling account in part for the low ingrowth of high-risk

trees from pulpwood size to sawtimber.

Discussion

The primary purpose of this research was to evaluate

strategies for management of merchantable-aged slash and

loblolly pine plantations with moderate to high incidence of

fusiform rust disease. Rust incidence in these plantations

ranged from 30 to 70 percent. Thinning based on the removal

Table N-Average periodic growth in thinned and nonthinned portions of nine loblolly

pine plantations after the selective thinning of fusiform rust-infected stems in the

Coastal Plain of Alabama and Georgia

Stand structure

Treatment Basal area Volume Live trees Sawtimber a

Thinned

Initial 97 2,277 333 46

5 years 117 2,732 305 103

10 years 127 3,158 266 142

Difference 30 881 -67 96

Nonthinned

Initial

7 yeas

10 years

Difference

122 2,803 464 42

144 3,561 405 114

142 3,489 316 148

20 686 -148 106

Ft2/acre FP/acre No./acre NoJacre

” Trees 2 9.0 in. diameter at breast height.
of trees with severe to moderate fusiform rust galls on the

main stem was the primary treatment imposed. In contrast

with conventional silvicultural thinnings, little attention was

given to establishing predetermined residual stand densities

or fixed spacings. The selective removal of moderate- and

high-risk trees provided an immediate return on trees that

had a high probability of dying before final stand harvest. In

addition, thinning provided improvements in stand quality

and enhanced individual tree growth. Overall quality of the

residual trees was excellent after thinning. In the slash and

loblolly pine plantations, only 7 and 8 percent of the residual

trees, respectively, had severe stem girdling galls.

Rust severity is an important consideration when developing

management strategies to reduce losses from fusiform rust.

Trees with severe stem girdling grew significantly less than

rust-free trees or trees with small or moderate amounts of

stem girdling. A large portion of the rust-associated

mortality in the study appeared directly related to gradual

reduction in tree growth caused by severe stem girdling. In

addition, severe stem girdling equates to lower tree quality

and value (Clark and McAllister 1998). Rust severity was

more important in assessing the potential impact of rust than

incidence alone. Although there was a direct and significant

relationship between rust incidence and percentage of highrisk trees in the study plantations (Belanger and Zarnoch

1991), it is unknown whether these associations apply

throughout the South.

Accumulative 1 O-year losses from fusiform rust in

nonthinned plots were similar for both species. Loblolly pine

sustained large additional losses from attack and spot

spread by the SPB. Total tree mortality and volume loss

caused by epidemic SPB activity were approximately twice as

much in nonthinned study plots as in thinned plots. These

findings are in agreement with survey results in Texas

reported by Cameron and Billings (1988). The occurrence

and severity of SPB activity are expected to increase as total

volume, stand structure, and average age of loblolly pine

plantations continue to increase throughout the South.

Hedden (1983) indicated that reductions in stocking levels

by thinning lowers the probability of SPB attack and

subsequent spot spread. Results from this study confirm

these predictions.

Losses from SPB attack were minimal in the slash pine

plantations. Probable reasons are that (1) slash pine is highly

resistant to successful SPB attack and spot spread, and (2)

beetle populations were endemic in the slash pine study

areas during the lo-year measurement period.

Field surveys and laboratory testing were conducted to

assess levels of H. annd~um in the plantations. Visual field

examination of 3,832 secondary root systems showed that

symptoms of H. annosum were present on 16 percent of the

roots sampled. This low level was fairly consistent within

slash and loblolly plantations and within thinned and

nonthinned treatment areas. However, laboratory testing of a

subsample of 466 symptomatic roots isolated positive H.

annosum cultures from only 4 percent of the roots. Results

from the laboratory testing agree with the low susceptibility

rating for annosum root rot associated with soil type

(Froelich and others 1966). No mortality was attributed to

root rot fungi in slash or loblolly pine plantations.

Trends in periodic stand growth and total volume

production were similar for slash pine and loblolly pine

plantations. Standing volumes at the end of the lo-year

study period were greater in nonthinned portions of the

plantation. Periodic stand growth, however, was greater in

thinned portions of the plantations. Total volume production

(thinned volume added to standing volume) was also greater

in thinned plots than nonthinned plots. Bennett and Jones

(1983) noted that in free-to-grow stands, where mortality is

not a factor, merchantable thinning will not increase total

merchantable cubic volume yield. In this study, mortality was

a significant factor. Rust-associated mortality reduced

volume growth and production in the slash pine plantations.

Losses from rust and the SPB had a severe impact on total

production in the loblolly plantations.

In summary, silvicultural and pest management gains from

the selective thinning of rust-infected trees include

l a significant improvement in the quality of trees in the

residual stands;

l a reduction in growth losses caused by fusiform rust;

l the salvage of potential mortality;

l intermediate cash returns;

l a reduction in the potential for SPB attack and spot

spread;

l an accelerated growth of the residual stands; and

l the ingrowth of quality sawtimber.

The major disadvantages of this specialized type of thinning

include

l the costs of selective marking and harvesting; and

l lack of control over predetermined stand spacing or

stocking levels.

1 2
Results, methodology, and practices developed during this

study can be incorporated into conventional thinning

programs used to regulate stand density, accelerate tree

growth, and achieve specific management objectives. Trees

with severe rust galls should be removed during all

intermediate silvicultural practices. Guidelines have been

developed for selecting trees for removal based on degree of

stem girdling, number of galls, and location of galls

(Belanger and others 1991). Removal of high-risk galled trees

will improve the quality, growth, and general health of the

residual stand.

Acknowledgments

The research reported in this paper was funded in large part

by the Integrated Forest Management Cooperative at the

University of Florida and the Integrated Pest Management

Program, U.S. Department of Agriculture, Forest Service.

Special recognition is given to Union Camp Corporation

(now International Paper Co.) for providing the land base,

technical support, and maximum cooperation from the

inception to the completion of the study. The authors

sincerely thank Jimmy Seckinger, Jim Sullivan, and John

Williams who assisted and made important contributions to

this cooperative research program.

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stands in Florida, Georgia, and the Carolinas. Southern Journal of

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13
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14


Belanager, Roger P.; Miller, Thomas; Zarnoch, Stanley J.; Fraedrich, Stephen W.; Godhee, John F.

2000. An integrated approach toward reducing losses from fusiform rust in merchantable slash and loblolly pine

plantations. Res. Pap. SRS-23. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern

Research Station. 14 p,

The primary objective of this study was to evaluate the selective thinning of trees with rust galls as a means of

reducing losses to the fusiform rust (Cronartium yuercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme) disease in

merchantable slash (Pinus eUioftii Engelm. var. elliottii) and loblolly (P taedu L.) pine plantations, Additional

objectives were to assess the post-thinning occurrence and impacts of southern pine beetles (Dendroctonus

fronfulis Zimm.) and annosum root rot (Heterobasidion annosum Fr.). Nineteen rust-infected plantations were

selected in Alabama, Georgia, and South Carolina to represent a wide range of stand and rust conditions. Thinnings

were based primarily on the removal of trees with severe and moderate stem girdling caused by fusiform rust galls.

Approximately 750 acres were thinned operationally to salvage potential mortality; 2,250 nonthinned acres

served as controls. Study plots were surveyed annually for 10 years to determine the amount and causes of

mortality. Stand growth and development were evaluated at the end of 5- and IO-year periods after treatment.

Removal of rust-infected stems greatly improved the quality of trees in the residual stands. The periodic diameter

growth of individual dominant and codominant slash and loblolly pine trees was affected by the extent of stem

girdling. Trees with severe stem girdling (250 percent) grew significantly less than gall-free trees or trees with

small or moderate stem girdling. Trends in periodic stand growth and total volume production were similar for slash

and loblolly pine. Standing volume at the end of IO years was greater in nonthinned portions of the plantations

than in thinned portions. However, periodic stand growth and ingrowth of rust-free sawtimber (29 inches in

diameter at breast height) were greater in thinned portions of the plantation. Rust-associated mortality was the

primary factor that reduced volume growth and production in slash pine plantations. Losses from fusiform rust and

the southern pine beetle had a severe impact on total production in the loblolly plantations. Thinning significantly

reduced losses from both of these forest pests. Management implications can be incorporated into conventional

thinning procedures for regulating stand density, increasing growth, and improving stand health.

Keywords: Annosum root rot, forest health, integrated pest management, Pinus elliottii Engelm. var. elliottii,

Pinus tueda L. southern pine beetle, thinning.

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