United States 

Department of 

Aariculture Sugarberry Dieback and Mortality .+ - 

Forest Service in Southern Louisiana: 

Cause, Impact, and Prognosis 

Southern J.D. Solomon, A.D. Wilson, T.D. Leininger, D.G. Lester, 

Research Station C.S. McCasland, S. Clarke, and (2. Affeltranger 

Research Paper 

SRS-9 
Sugarberry Dieback and Mortality 

in Southern Louisiana: Cause, 

Impact, and Prognosis 

J.D. Solomon, A.D. Wilson, T.D. Leininger, D.G. Lester, 

C.S. McCasland, S. Clarke, and C. Affeltranger 

Abstract 

A sudden widespread decline of sugarberry trees (Celtis laevigata) was 

observed in southern Louisiana during the period between the early fall of 

1988 and spring of 1990. Approximately 3 million acres or 5,000 square 

miles of forested lands were affected by the decline. In addition, sporadic 

reports of sugarberry decline also were reported at numerous locations in 

Mississippi. Investigations into the long list of potential causal agents led 

to the conclusion that the most probable causes of the damage were due to 

an opportunistic exotic insect pest, Tetragonocephalaflava, a psyllid that 

caused defoliation and twig dieback, followed by a hard freeze which 

killed new regrowth following the insect damage. The psyllid has a very 

narrow host range attacking only Celtis species. Many sugarberry trees 

that survived the decline event now appear to be slowly recovering. 

Keywords: Celtis laevigata, crown dieback, episodic event, exotic pest, 

psyllidae, sugarberry decline, Tetragonocephalaflava. 

Introduction 

Sugarberry (Celtis laevigata Willd.), a common, medium 

size tree of the Southern United States, comprises 40 to 80 

percent of the basal area in many bottomland hardwood 

stands, primarily on clay soils within the flood plains of 

major southern rivers and their tributaries. It is oAen planted 

as a shade and landscape tree in yards and along streets in 

residential areas (Kennedy 1990). The dry, sweet fruits are 

eaten by birds and wildlife in the late fall and winter months 

(Vines 1960). Sugarberry wood is used primarily in 

furniture manufacturing, but it is also used to produce 

dimension lumber, veneer, and containers (Kennedy 1990). 

The Mississippi Delta area of Arkansas, Louisiana, and 

Mississippi is the only region in the South that contains 

sufficient quantities of sawtimber-sized sugarberry to 

support commercial production (Smalley 1973). 

Southern Louisiana landowners reported a sudden and 

widespread dieback and decline of sugarberry in the late 

1980's and early 1990's (Coyer and others 199 1, Solomon 

199 1). The dieback event became very noticeable as trees 

began to die at an alarming rate. Although the cause of the 

dieback and mortality was not immediately apparent, 

landowners cited many possible causal agents ranging from 

adverse weather conditions and air pollutants to biotic pests. 

Numerous insect and disease pests of CeEtis spp. have been 

reported (Riley 1890, U.S. Depament of Agriculture 

1985), but no records describe dieback episodes like those 

in southern Louisiana. This paper provides descriptions of 

communications, contacts, and consultations with many 

scientists, professors, extension-service specialists, forestry 

consultants, and landowners. In addition, we present and 

discuss results of research from data collections and 

observations made on study plots, including analyses of 

samples collected during trips to the affected area, as well as 

followup observations of the study plots between 1988 and 

1996. We also discuss the most probable cause(s) of the 

decline based on the best information available from recent 

investigations. The objectives of this study were to 

investigate the cause(s) of sugarberry dieback and mortality, 

to assess the current status of symptoms, to evaluate the 

effects of the dieback, and to determine whether conditions 

were worsening, improving, or remaining static. 

Methods and Materials 

Scientists at the Southern Hardwoods Laboratory (SHL) 

made initial contacts in early 1989 with forestry consultants 

and landowners within areas affected by sugarberry decline. 

Samples of foliage, twigs, and branches collected from 

symptomatic trees by these cooperators were received for 

examination shortly after at the SHL. The scientists returned 

to the affected area to collect additional samples and study 

the problem in 1990. They interviewed a number of local 

residents to assess their observations. Some landowners had 

kept records of tree symptoms from the time they first 

observed the problem. Scientists from the SHL, Louisiana 

State University, and Forest Health Protection (US. 

Department of Agriculture, Forest Service, State and Private 

Forestry) met with landowners and forestry consultants to 

assess the problem. In an attempt to determine possible 

causes of the dieback problem, specialists were consulted 

and more local landowners were interviewed. Observations 

and records from these contacts are presented to provide 

some background and a chronology of the sugarberry 

dieback in southern Louisiana. 
Research study plots were installed in July 1991 within and 

outside of the area affected by sugarberry decline (fig, 1). 

Four variable radius study plots (BAF 5) were established 

randomly at each of four selected locations. Two sites in the 

affected area included a saw-log sized stand near Brusly and 

an open woodlot near Houma. Two additional sites were 

selected outside the affected area in a saw-log sized stand 

west of St. Francisville, and a similar saw-log sized stand 

southwest of Clinton. Data for the following variables were 

recorded for all trees over 3 inches in diameter at breast 

height (d.b.h.) in each plot: species, d.b.h., crown class, 

crown condition, injury by insects and disease, and whether 

the tree was alive or dead. Crown condition was measured 

by a visual assessment of the percentage of the total twigs, 

branches, and sprouts exhibiting dieback. The crown 

variables were rated using the following scale: 1 = 0 

percent, 2 = 1 to 10 percent, 3 = 1 1 to 33 percent, 4 = 34 to 

66 percent, 5 = 67 to 99 percent, and 6 = 100 percent, 

indicating the percentage of plant parts that were 

symptomatic. 

Two increment cores were taken from opposite sides of 12 

sugarberry trees at each of the 4 study sites. Annual growth 

increments from 1969 to 199 1 were measured to * 1 pm 

using a color scanner, desktop computer, and 

WinDENDROTM v. 6.0 tree ring analysis software (Regent 

A Clinton 

A St Francisville 

Figure 1-Area in southern Louisiana affected by sugarberry decline during and after the 1988-89 dieback episode. 

2 
Ltd., Quebec, Canada). Ring widths for each year at each 

site were averaged and plotted against time. Trend lines 

were fit to the data from each site using simple linear 

regression. 

A composite soil sample, composed of a mixture of five 

subsamples, was collected from the top 60 centimeters of 

soil at random locations within each plot to examine 

edaphic factors that may have contributed to the decline. 

Soil characteristics-including soil pH, cation exchange 

capacity (CEG), percent organic matter (percent OM), 

sodium concentration in parts per million, and extractable 

macronutrient and micronutrient levels in pounds per acre 

for phosphorus, potassium, calcium, magnesium, sulfur, and 

zinc-were measured by soil analyses. The soil texture at 

each plot site was classified as sandy, silty, or clayey. Any 

evidence or records of site disturbance, such as changes in 

drainage or flooding, were noted. 

Sugarberry trees were examined for the presence of fungal 

pathogens by collecting six samples each from twigs, 

branches, and roots. Samples were transported in plastic 

bags on ice to the laboratory for isolation and identification 

of pathogens. Insects from sugarberry foliage were sampled 

with sweep nets (25 sweeps per plot) and preserved for 

identification in the laboratory. 

Records of temperature and rainfall were examined for any 

radical departures from normal which might have adversely 

affected tree growth and physiology. Preliminary 

observations were made of any adverse effects from 

chemical pollutants. 

A small-scale survey of yard and street trees within 

residential areas was conducted in 1992 to provide 

additional data on the extent of sugarberry crown dieback 

and mortality. Five communities were selected for study 

along a north-south axis in the affected area. The 

communities included St. Francisville, Brusly, 

Donaldsonville, Thibodaux, and Wouma. The starting point 

within each community was randomly selected along a 

major road or street. Every third block having at least 3 

sugarberry trees, including street and yard trees on both 

sides of the street, was sampled systematically until 10 

blocks had been sampled. All sugarberry trees (including 

stumps) were scored as alive or dead, and the extent of 

crown dieback (twigs and branches combined) was rated 

using the scale described above. Followup observations in 

the affected area between 1993 and 1996 were made to 

identify any new defoliation and dieback as well as 

continuing tree recovery. 

Results 

History and Chronology 

Sugarberry trees exhibited light defoliation in the spring and 

noticeable premature defoliation in the late summer and 

early fall of 1988.Widespread defoliation occurred twice 

during the 1989 growing season, once in late spring and 

early summer and again in late summer and early fa1L2 

Foliage and twig samples from affected trees near 

Thibodeaux were submitted to the SHL on June 9, 1989. 

The leaf samples exhibited many white, silky covers 

containing psyllid nymphs which were identified as 

Tetragonocephala~ava Crawford (Sternorrhycha: 

Psyllidae). Isolations failed to yield any disease-causing 

agents. 

Dieback of sugarberry trees became increasingly noticeable 

the following spring (1990). In early May 1990, SHL 

employees met in Baton Rouge with representatives from a 

forestry consulting firm, Forest Health Protection, Louisiana 

State University, and several private landowners to evaluate 

the problem. They examined many affected trees in the 

Baton Rouge area and visited a 2,000-acre natural stand of 

sawtimber near Brusly which contained a significant 

component of sugarberry. Most trees examined had 

noticeable crown (twigs and branches) dieback. The timber 

tract had been marked for a sugarberry salvage cut because 

the landowner feared that all the sugarberry trees were 

going to die. On one side of the tract, loggers were cutting 

every sugarberry tree that was large enough to produce 

either saw logs or pulpwood. A number of other timber 

tracts in the area were being marked for salvage by 

landowners or forestry consultants who feared widespread 

sugarberry mortality. 

Large numbers of sugarberry trees of all age classes were 

affected on the 2,000-acre Brusly tract. Twig and branch 

mortality exceeded 50 percent on trees that were felled and 

closely examined. Some small cankers were found by 

removing bark from the twigs, but beyond the cankered 

areas, the tissues were white and normal with no significant 

Personal communication. 1990. O.E. Monier, Jr., Vice President, Houma 

Fabricators, Inc., Houma, LA 70360; and Dale Pollet, Extension 

Entomologist, Louisiana State University, Baton Rouge, LA 70803. 

Personal communication. 1990. Dale Pollet, Extension Entomologist, 

Louisiana State University, Baton Rouge, LA 70803; and Severn 

Doughtry, Extension Entomologist, LSU Agricultural Center, 107 Bronson 

Hall, 1 University Place, Louisiana State University, Shreveport, LA 

71 115. 
browning, streaking, or staining. Disks cut from large 

branches, the bole, and at stump level were clear and white 

with no evidence of stain or decay. However, the fresh cut 

surfaces felt exceptionally dry. There was no visual 

evidence of root rot or fungal fruiting. Eleven insects were 

found feeding on foliage, twigs, and trunks, but none was 

implicated in causing the dieback. The psyllid, 7: Ma, 

prevalent in 1989, was not found in 1990. 

Further investigations were conducted by examining trees 

from Baton Rouge southward through Donaldsonville, 

Napoleonville, and Thibodeaux to Houma. Sugarberry 

dieback was progressively more noticeable southward from 

Baton Rouge. High levels of dieback were present in a large 

percentage of sugarberry trees along streets, in yards and 

woodlots, and along roadsides and ditch banks. In May 

1990, trees in the Baton Rouge-Brusly area seemed to have 

been affected very recently, because almost all the dead fine 

twigs and small branches were still intact. This indicated 

that the dieback probably occurred in late 1989 and early 

1990. Further south in the Thibodeaux, Raceland, and 

Houma areas, the dieback also appeared to have occurred 

recently, but there the dead twigs on some trees had begun 

to fall off leaving small and large bare branches in the 

crowns. In these areas, twig dieback could have begun as 

early as 1988 or early 1989. 

Symptomology 

Sugarberry trees examined during 1988 and 1989 appeared 

chlorotic and exhibited premature defoliation. However, 

affected trees quickly refoliated. Yellowing leaves, 

premature leaf drop, and refoliation occurred at least once in 

1988 and twice in 1989. Wen trees refoliated in 1989, new 

foliage appeared on the bases of twigs and branches, leaving 

many twigs and branch ends bare (fig. 2A). The bare branch 

ends eventually broke off to form larger bare branch 

terminals (fig. 2B), a process that was especially noticeable 

after the second defoliation in 1989. After that defoliation, 

stressed trees grew many epicormic sprouts and suckers 

along their large branches and trunks (fig. 2C), which 

were observed on sugarberry trees in the woods (fig. 2D) 

and on individual trees in residential yards (fig. 2E). The 

severe chlorosis and premature defoliation symptoms did 

not appear in 1990, although for years following the damage 

in 1989 most sugarberry trees in the affected area exhibited 

severe twig and branch dieback in the upper crown, 

epicormic branches, and suckers along the larger branches 

and trunk. Leaves on surviving basal portions of twigs and 

branches were smaller than normal, slightly chlorotic, and 

often exhibited necrotic margins. Leaves on new sprouts 

were generally green and nearly normal in size. Much of the 

sprouting was clustered along large branches and trunks, 

giving trees the striking water-sprout appearance typical of 

trees that have lost apical dominmce due to top dieback 

(fig. 2F). Symptoms were so noticeable in 1989 and 1990 

that many landowners feared widespread mortality was 

imminent. 

Impact 

Range and delineation-The range of area affected by 

sugarberry decline was delineated, in part, using 

infomation from the Louisiana Forestry Commission, 

Louisiana State University, forestry consultant firms, and 

landowners. To more exactly defme the affected area, the 

Louisiana State University Staff conducted an aerial survey. 

However, that and other aerial surveys were inadequate to 

distinguish damaged sugarberry from healthy sugarberry. 

To date, our best estimation of the area affected by 

sugarberry decline includes land within imaginary lines that 

extend from Baton Rouge southward to just beyond Houma, 

and west to Lafayette and Opelousas. Lighter symptoms of 

the decline extend to the vicinity of Jennings, and east to 

La Place and Paradis (just west of New Orleans). The total 

area included about 5,000 square miles, or 3 million acres, 

of southern Louisiana. Sporadic reports of sugarberry 

dieback also were noted in the Starkville and Jackson areas 

of Mississippi. 

Tree crown diebaek and mortality-The extent of 

sugarberry crown dieback and mortality in forests and 

woodlots near St. Francisville, Clinton, Brusly, and 

Houma in 199 1 and 1992 is shown in table 1. In 1991, 

average crown ratings of 1.3 to 1.5 for sugarberry at the 

St. Francisville and Clinton sites (outside the affected area) 

indicated normal twigs, branches, sprouts, and foliage. Twig 

and branch ratings of 2.6 and 2.5 at Brusly indicated 

moderate sugarberry dieback, but new sprout growth and 

foliage were green, indicating little evidence of continuing 

dieback. At the southern most location near Houma, dieback 

ratings averaged 5.0 and 4.5, respectively, for twigs and 

branches, indicating that severe dieback had occurred. At 

Houma, ratings for sprout growth and foliage were slightly 

worse than those at other locations, but sprout growth and 

foliage were in fair-to-good condition, indicating an 

apparent recovery. 

Ratings in 199 1 for the crown variables of species other 

than sugarberry, including Nuttall oak, water oak, willow 

oak, overcup oak, water hickory, green ash, American elm, 

sweetgum, cottonwood, black willow, honeylocust, 
Figure 2-Symptoms of sugarberry dieback and decline observed in southern Louisiana. (A) Twig and branches with bare ends following defoliation, 

(B) breakage of branches following defoliation, (C) epicormic sprouts and suckers along the main branches and trunk of a tree in an open field, (D) dieback 

and epicorrnic branching of sugarberry trees in a woodland setting, (E) twig dieback and epicormic branching of a sugarberry tree in a residential yard, and 

(F) water sprouts arising along large branches and trunks of large trees. 
sycmore, red maple, pecan, and boxelder were considered 

nomal, i.e., those species exhibited no comparable dieback 

(table 1). Average ratings for crown variables at Houma 

were not noticeably different from those at other locations, 

indicating that the cause of serious dieback in sugarberry 

trees did not adversely affect other tree species. 

Crown ratings taken in 1992 showed that there remained 

marked differences in the extent of sugarberry dieback 

between sites outside and inside the affected area (table 1). 

However, most dieback had occurred prior to 1991, and we 

observed little subsequent dieback. A comparison of crown 

ratings indicated very little change in dieback between 1991 

and 1992 for sugarbew or any other species. Although 

Hurricane Andrew blew through the study area in August 

1992 causing considerable damage to some trees in the 

study, such damage could generally be distinguished from 

dieback. 

Five (1 5 percent) of the sugarberry plot trees near Houma 

died in 199 1. Mortality increased to 22 percent in 1992 

(table 1). Trees in plots at St. Francisville, Clinton, and 

Brusly showed some wind damage, but none of the standing 

sugarberry trees bad died. Among the other species, two 

oaks had died, one each in the St. Francisville and Brusly 

plots. 

Table l-Crown dieback ratings and mortality of sugarberry compared to other tree 

species within study plots in southern Louisiana from evaluations in 1991 and 1992 

Dieback Rating" 

Number Percent 

Location of trees mortality Twigs Branches Sprouts Leaves 

Sugarberry 

Houma 

Brusly 

Clinton 

St. Francisville 

Other Species 

Houma 

Brusly 

Clinton 

St. Francisville 

Sugarberry 

Houma 

Brusly 

Clinton 

St. Francisville 

Other Species 

Houma 

Brusly 

Clinton 

St. Francisville 

1991 Evaluations 

1992 Evaluations 

" Dieback rating scale: 1 = 0 percent, 2 = 1 to 10 percent, 3 = 11 to 33 percent, 4 = 34 to 66 percent, 5 = 67 to 99 

percent, 6 = 100 percent, where percentages indicate percent dieback (mean k SEM) of twigs, branches, sprouts, 

and leaves. 
Effects on sugarberry reproduction-During 199 1 and 

1992, sugarberry seedlings and saplings in study plots were 

counted. Reproduction was evident in most plots. Combined 

seedling and sapling counts per plot ranged from 0 to 5 in 

the St, Frmeisville and Clinton plots, 1 1 to 19 in the Brusly 

plots, and 0 to 10 in the Houma plots. Dieback on 

reproduction varied from light to moderate at the Brusly and 

Houma sites. 

Analysis of sugarberry growth trends-Simple linear 

regression models, with year as the independent variable 

and ring width as the dependent variable, indicated that year 

was not a good predictor of ring width. The data were not 

distributed normally, precluding comparisons of slopes 

between sites using these models. However, trend lines 

combined average annual increments for the previous 

4 years (fig. 3A). In 199 1, average annual growth at Houma 

was about 60 percent less than the combined average 

growth between 1986 and 1989, indicating that sugarbew 

growth at the Hourna site decreased sharply immediately 

following the 1988-89 severe dieback. The lack of a growth 

decrease in 1989 suggests that the sugarberry trees had 

already completed most of their annual growth prior to the 

first defoliation in late spring or early summer. The 

defoliation and refoliation events that occurred in 1988 and 

1989 would have severely reduced or eliminated starch 

reserves in the roots. Reductions in sugarberry annual 

growth in 1990 and 199 1 likely were due to the 

physiological stress caused by the three earlier defoliations, 

reductions in starch reserves caused by refoliation, and the 

based on simple linear regressions do suggest differences in concomitant reductions in carbon replenishment resulting 

the amount and rate of growth among the sites (fig. 3). from smaller leaves and reduced crowns. At the Brusly, 

Sugarberry trees at Houma had average annual ring widths St. Francisville, and Clinton sites, sugarberry ring widths for 

that were about double those at Brusly, St. Francisville, and 1990 and 199 1 were not far removed from the trend lines 

Clinton. Average growth rates of trees at all four sites were for these sites, a condition that indicates normal growth (fig. 

declining, but the average growth rate of trees at the Houma 3B-D). The amount of sugarberry dieback at Brusly, within 

site was declining more rapidly than at the other three sites. 

The rate-of-growth decline of trees at Brusly was only 

slightly greater than those at the St. Francisville and Clinton 

sites. Differences in average ring widths and average growth 

rates among sites likely were due to differences in stand 

density, stand age, soil type, and historical site-use factors 

which were not documented. 

The average annual increment for sugarberry trees at the 

Houma site in 1990 was about one-third less than the 

the affected area, apparently was not severe enough to 

reduce radial growth. 

Dieback and mortality of street and yard treesObservations of noticeable sugarberry dieback and mortality 

within residential areas prompted a survey of trees along 

streets and in yards. The survey was conducted in 1992 in 

St. Francisville, Brusly, Donaldsonville, Thibodeaux, and 

Houma. The results of that survey are given in table 2. 

Table 2-Survey of crown dieback and mortality of sugarberry trees in residential areas of southern 

Louisiana in 1992 

City blocks No. trees Tree size distribution (%)" Percent Crownb 

Location surveyed examined Sapling Pole Saw log mortality rating 

Inside decline area 

Brusly 10 116 6.0 (0.9) 37.9 (28.5) 56.1 (33.6) 12.9 4.7% 1.1 

DonaldsonviIle 10 9 1 5.5 (3.3) 35.2 (35.2) 59.3 (44.0) 16.5 4.0 0.1 

Houma 10 104 0.0 (0.0) 25.0 (18.3) 75.0 (63.5) 18.3 4.9 k 0.1 

Thibodeaux 10 117 6.8 (6.0) 20.5 (17.1) 72.7 (55.6) 19.7 4.2 k 0.1 

Outside decline area 

St. Francisville 10 67 10.4 (3.0) 29.9 (9.0) 59.7 (9.0) 1.5 1.9 % 0.1 

" ~ercentage of survey trees in each size class (size-class distribution). Values in parentheses indicate the percentage of surveyed trees 

that had crown ratings of 3.0 or greater (exhibiting substantial symptoms of decline). ' Crown rating scale: I = 0 percent, 2 = 1 to 10 percent, 3 = 11 to 33 percent, 4 = 34 to 66 percent, 5 = 67 to 99 percent, 6 = 100 percent, 

where percentages indicate percent dieback (mean + SEM) of twigs and branches (combined) on living trees. 

Every sugarbew examined in the affected area exhibited 

moderate to serious dieback, as indicated by crown ratings 

>4.0. Mean crown dieback ratings increased progressively 

from north to south and ranged from 4.0 in Donaldsonville 

to 4.9 in Houma where the dieback was most noticeable. 

Trees surveyed in St. Francisville and Clinton, outside the 

affected area, had an average crown rating of 1.9, indicating 

relatively healthy crowns. 

Many dead sugarberry trees that had been cut were 

identified by the remaining stumps. Interviews with several 

homeowners revealed that the cut trees had exhibited severe 

twig and branch dieback. Therefore, dead tree counts 

include both standing trees and stumps. Generally, the 

incidence of sugarberry mortality increased southward from 

Brusly where 12.9 percent mortality was recorded, to 

Houma and Thibodeaux where mortality rates of 18.3 and 

19.7 percent were recorded, respectively. Only 1 of 67 trees 

examined in St. Francisville and Clinton had died. 

Trees surveyed within five towns inside and outside the 

affected area were predominantly saw-log sized trees (56 to 

75 percent) with one-fourth to one-third pole size and 

< 7 percent saplings. A further analysis of the sizes of trees 

with symptoms of crown dieback and decline (crown rating 

r 3.0) indicated that the percentage of symptomatic trees 

increased with age. For example, <I 0 percent of saplings at 

all locations within the affected area exhibited symptoms of 

dieback, while 17.1 to 35.2 percent of pole-sized trees, and 

33.6 to 63.5 percent of saw-log sized trees were 

symptomatic. These results may suggest either that older 

trees are more frequently (possibly preferentially) affected 

by or were more susceptible to damage by the causal agent. 

Factors Considered as Possible Causes of the Dieback 

Residents, landowners, and foresters living in the affected 

area, as well as professionals who have examined dying 

trees, have proposed several factors as the cause of 

sugarberry dieback. Some of the potential causes, including 

winter damage, soil factors, herbicide drift, air pollution, 

and specific insect and disease pests are discussed here 

along with the evidence available to support each 

explanation. 

Climatic factors-Some local residents and extension 

specialists suggested that the massive, rather sudden dieback 

and mortality of sugarberry in southern Louisiana was due 

to extremely cold weather in December 1989. According to 

official weather records, daily low temperatures ("F) in the 

affected area were as follows: 

Brusly 32" 16" 9" 9" 11" 17" 28" 

Houma 37" 22" 10" 11" 15" 22" 32" 

This early winter cold period apparently caused serious 

dieback and mortality in scattered Chinese tallowtree, an 

exotic species known to be susceptible to frost injury. 

However, except for sugarberry, severe dieback apparently 

did not affect other tree species in the area. Moreover, at 

Clinton (outside the affected area) temperatures dropped to 

lows of 3 1 ", 12", 5", 1 ", 17", 28", and 30" on the same 

days listed above, yet sugarberry trees there were not 

adversely affected. At Mississippi State University, where 

sugarberry dieback and mortality were noted, temperatures 

for the same time period dropped to 21°, lo, - go, - 3", 3", 

27", 25 ", respectively. Across the State at Stoneville, low 

temperatures were 20°, 2", 1 ", 1 ", 3", 28", and 29" for the 

same days, yet no dieback or mortality occurred. These 

findings suggest that low temperatures alone were not 

responsible for the dieback and mortality. However, the low 

temperatures coupled with other factors could have 

contributed to the seriousness of the problem. 

Examination of southern Louisiana precipitation records 

revealed above average rainfall in 1988 (Baton Rouge 

totaled 76.04 inches, or 20.27 inches above normal) and 

1989 (Baton Rouge totaled 88.32 inches, or 32.55 inches 

above normal). This was followed in 1990 by near average 

precipitation. Although the flooding history of these sites 

was not studied, precipitation conditions during that period 

likely would not have caused the sudden and severe 

dieback. 

Soil Factors 

Comparisons of physicochemical properties and extractable 

nutrient levels in soil samples from study plots inside and 

outside of the affected area indicated some differences in 

certain soil properties that may have influenced the health 

and susceptibility of sugarberry trees to damage by the 

causal factor (table 3). Among the physical properties, the 

pH of soils inside the affected area at Houma was 

significantly more acidic than on sites outside of the damage 

zone. The CEC of soil samples at St. Francisville and 

Clinton (outside the affected area) were appreciably lower 

than those of soils within the affected area. Soils inside and 

outside the affected area differed very little in percent OM. 

Nutrient levels of soils within the affected area were higher 

in potassium, calcium, magnesium, and sodium than at St. 

Francisville or Clinton, but the phosphorus level was higher 
TabIe 3-Analyses of soil samples taken from study piots inside and outside of areas affected by sugarberry decline 

Physicochemical propertiesu Nutrient compositionb 

Plot location PH CEC %OM P K Ca Mg S Zn Na 

Brusl y 6.3 40.0 55.5 ~0.6 1.78 4 0.12 72.3 A 4.1 640.8 i 1.0 14,313 * 200 4,100 4 122 255.8 4 17.5 5.6 10.4 327.8 A 15.2 

Houma 5.5 k0.3 52.1 47.0 3.56 4 0.69 69.8 A 15.8 589.8 k 23.0 12,643 41,810 3,443 ~403 512.8 198.6 11.9 42.2 305.3 A 37.8 

Clinton 6.3 10.1 42.1 A0.8 2.17 A 0.10 109.0 & 5.8 486.5 i 10.5 10,103 4 53 3,062 A 162 312.3 A 13.7 13.3 40.4 222.3 A 12.7 

St. Francisville 7.5 1f0.0 26.9 A 1.6 1.54 4 0.02 149.3 A 3.9 280.5 1f 13.5 7,344 A 474 1,957 1201 221.0 A 2.5 10.4 i0.3 141.5 k 8.6 

"Symbols: pH = -log [H+], CEC = cation exchange capacity, % OM = percent organic matter content. 

Extractable nutrient levels for phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), and zinc (Zn) are in pounds per acre; sodium (Na) 

is in parts per million. 

outside the affected area than inside. Differences in the 

physicochemical properties and nutrient composition of 

soils inside and outside of the affected area could have 

contributed to the response of trees to dieback, but the 

magnitude of differences in these edaphic factors was not so 

large as to indicate a physiological cause for the dieback, 

e.g., nutrient deficiencies, nutrient toxicities, or pH-induced 

mobilization of toxic heavy metals. 

Herbicide drift-Until about 1990, herbicides, especially 

glyphosates like Palado, Polaris, and Roundup, were used 

extensively for weed control in southern Louisiana 

sugarcane fields. Several residents and landowners in the 

affected area suggested that the extensive use of these 

herbicides and application drift were responsible for the 

sugarberry dieback. However, twig and branch samples 

collected from declining sugarberry trees in 1989 were 

analyzed chemically at a reputable State chemical 

laboratory and did not contain glyphosate. Moreover, 

sugarberry stands with dieback symptoms were observed at 

a number of locations in southern Louisiana that were many 

miles from any treated sugarcane fields. Trees exhibiting the 

same dieback also were observed at Starkville and Jackson, 

MS, where there had been no heavy use of herbicides. 

Furthermore, no sugarberry dieback was reported or 

observed in areas like the Mississippi Delta, where the 

species is common and glyphosate herbicides are used 

extensively. The evidence clearly does not support the 

hypothesis that herbicides were the primary cause of 

sugarberry dieback. 

Air pollution-Some landowners believe that toxic 

pollutants released into the air by large chemical plants in 

the affected area caused the problem. Indeed, there are 

hazardous waste incinerators as well as a large chemical 

manufacturing industry in southern Louisiana. One 

concerned landowner who kept notes of various biological 

events beginning in the mid- 1980's strongly suggested that 

airborne chemical pollutants were responsible. His notes 

describe at least a dozen deciduous and coniferous trees that 

exhibited symptoms ranging from top dieback, thin crowns, 

decay, poor nut crops, abnormal sprout growth, and a 

blighted appearance to dieback and repeated leaf-out during 

the growing season. Furthermore, he plotted on a map a 

triangular area extending from Baton Rouge southeastward 

to the vicinity of Larose, Houma, and Therist, where the 

symptoms were most severe. 

A literature search failed to reveal any previous episodes of 

pollutant-related dieback on sugarberry or other Celtis 

species. Several references stated that Celtis spp. were 

tolerant andfor resistant to several pollutants produced by 

nitrogenous fertilizer plants, airborne fluoride, and chlorine 

from winter road salting (Klincsek 1986, Kovacs and 

Klincsek 1982, Rhoads and Brennan 1975). Hepting (1971) 

reported that sugarberry was among the species most 

resistant to air pollution in the Houston, TX, area. 

Additionally, C. occidentalis, a closely related species, has 

been reported as quite tolerant to urban pollution in general 

(Kovacs and Klincsek 1982). Although our studies revealed 

some decline symptoms among other tree species, none 

exhibited the sudden and widespread dieback found in 

sugarberry. If airborne pollutants had caused the dieback, 

other species would have been affected as well. Moreover, 

sugarberry dieback was common in areas quite distant from 

large chemical plants. Although chemical pollutants could 

have stressed sugarberry trees, it appears that factors other 

than pollutants probably contributed more to the problem. 

Diseases-Sixteen genera of fungi as well as bacteria were 

isolated from branch and root samples of sugarberry trees 

on plots both inside and outside the affected area (table 4). 

fisarium species were isolated most often from sugarberry 

tissue, but Fusaria were readily found inside and outside the 
Table 4-Microorganisms isolated July 1991 from declining sugarberry trees in study plots of 

southern Louisiana 

Number of plots fkom which microbes were isolateda 

St. Francisville Clinton Bruslv Houma 

Microorganism Branch Root Branch Root Branch Root Branch Root 

Hyphornycetes 

Aspergillus sp. 

Fusarium sp. 

Penicillium sp. 

Oidiodendron sp. 

Nigrosporium sp. 

Alternaria sp. 

Fusicoccum sp. 

Agonomycetes 

Rhizoctonia sp. 

Oomycetes 

Pythium sp. 

Zygomycetes 

Mucor sp. 

Libertella sp. 

Coelomycetes 

Phoma sp. 

Phomopsis sp. 

Pestalotia sp. 

Dothiorella sp. 

Basidiomycetes 

Auricularia sp. 

Procaryotes 

Actinomycetes 

Bacteria 

Total 22 14 14 20 18 20 16 16 

" Microbe incidence is indicated by the number of study plots at each location from which each microbe was isolated. Four 

study plots were established at each location. 
affected areas. Species of Mucor, Penicillium, dot hi or el!^, 

and bacteria were somewhat more common kvithin the 

dieback area, but also were present outside. A 

Bok-ryod@lodia species was isolated from other sugarbew 

samples near Plaquemine. Xone of these microorganisms 

previously has been implicated in causing severe dieback 

and mortality of sugarberry (Hepting 197 1). Leaves 

collected from affected sugarberrq." trees in southern 

Louisiana in 1990 and 1992 were submitted to the 

University of Califomia to be tested for the presence of 

mycoplasma-like organisms (MLO's) using a 

deoxyribonucleic acid (DNA) probe (hybridization blot). 

Leaves tested negative for ML07s. Symptoms of a ring spot 

virus were observed on isolated sugarbeny foliage near 

Houma in 1992. In a greenhouse test, an unsuccessful 

attempt was made to mechanically transmit the ring spot 

virus from symptomatic to asymptomatic leaves of 

sugarberry saplings. It is likely that the virus was 

transmitted to the sugarberry by an insect vector. However, 

the mildness of the virus symptoms would not have likely 

resulted in sugarberry dieback. 

A literature review revealed a number of leaf-spot fungi, 

powdery mildews, witches' brooms, and bole rots common 

to the species, but none has caused serious dieback and 

mortality (Hepting 197 1). However, dead branches and 

branch stubs provide excellent entry sites for many species 

of wood-rotting fungi given the extensive crown dieback 

and slow wound-healing ability of sugarberry. Predictably, 

then, the incidence of wood decay fungi in timber stands 

and residential areas would be high for many years and 

could contribute to such a decline following the primary 

damage. Nevertheless, diseases do not appear to have 

caused the sugarberry dieback. 

Insects-Twenty-six species of insects were collected from 

sugarbeny trees in the affected area between 1990 and 

1993, but most were in relatively small numbers. The 

insects most commonly collected were hackberry butterfly 

larvae, Pachypsylla leaf-gall insects, cecidiomyiid leaf-gall 

insects, tussock moth larvae, forest tent caterpillar larvae, 

and Agrilus beetles. None of these was present in numbers 

sufficient to have caused the degree of dieback that 

occurred. However, there appeared to be a strong 

relationship between a psyllid insect (T: flma), which was 

present in very large numbers in 1988 and 1989, and the 

onset of sugarberq dieback during the same time period. 

White tests (nymphal coverings or cases) appeared in mass 

on the forest floor (fig. 4A). As mentioned earlier, 

sugarberry leaf and twig samples submi~ed from a location 

near Thibodeaux in June 1989 contained many of these 

small, white insect tests. Each test was very white, round 

[4 to 6 millimeters (mm) in diameter], flat to dome-shaped, 

silky, flaky, very thin, and aaached to the undersides of 

leaves (fig. 43). Nearly every leaf had one to several of 

these white insect tests. Underneath each test was a psyllid 

nymph (fig. 4C) subsequently identified as 7: ma. Adults 

were 3.75 to 4.25 mm long with expanded wings and 

resembled tiny cicadas (fig. 46)). 

Personnel from the Louisiana Agricultural Extension 

Service and Louisiana State University at Baton Rouge 

confirmed that there had been a heavy infestation of T. Jlava 

in southern Louisiana in 1988 and 1989. Local county 

agents received reports from residents that indicated the 

adult psyllids were so numerous that they clogged air 

conditioner filters. Sugarberry trees reportedly were 

defoliated by the psyilid infestation in the late summer and 

early fall of 1988. In May and June of 1989, and again in 

August and September, sugarberry trees were infested with 

71 Pava and sustained two heavy defoliations. During these 

infestations, there was repeated leaf drop and refoliation 

accompanied by prolific sprouting on branches and trunks. 

Sugarberry dieback was localized in areas of Mississippi 

during the same time period. Observations in Mississippi 

supported the findings in southern Louisiana and hrther 

implicated T. Java as the causal agent. Professors from 

Mississippi State University and scientists from the SHL 

observed a heavy infestation of T. ftava that caused a 

noticeable premature leaf drop on sugarberry trees on and 

around the Mississippi State University campus in the fall of 

1989. The ground under many large sugarberry trees near 

the football stadium and the cooperative extension building 

was covered with freshly fallen leaves. The leaves contained 

so many white tests over the psyllid nymphs that the ground 

appeared to be covered with a light snow. The following 

spring and summer (l990), campus sugarberry trees were 

very slow to produce new leaves, and a high proportion of 

the twigs and branches were dead or dying. Affected trees 

produced profuse sprouts along Iarge branches and trunks, 

much like those observed after the heavy psyllid-caused 

defoliation in southern Louisiana. Survey responses from 

county extension officers throughout Mississippi revealed 

that nymphal tests were observed in nine counties along a 

roughly southwest-to-northeast line extending from 

Wilkinson to Pontotoc and Lowndes C~unties.~ This linear 

Personal communication. 1997. Dr. James Jmatt, Extension 

Entomologist, Box 9775, Mississippi State University, Starkville, MS 

39762. 
Figure 4-Observed life stages of psyllid, Tetragonocephalaflava. (A) White tests (coverings) resting on leaves in litter on the forest floor; (B) closeup of 

nymph tests (on the underside of sugarberry lea@ (C) scanning electron micrograph of nymph, scale bar = 0.1 pM, x 41 magnification; and (D) adults of 

psyliid. 
cluster of sightings may indicate that the insect had been 

dispersed by wind from Louisiana. Nymphal cases also 

were obsewed in a 10" countp (Harrison) in the 

southeastern corner of the State. 

Discussion 

The evidence in this report suggests that the psyllid T. Java 

alone could have caused the sugarberry dieback. A highly 

unusual, exceptionally heavy infestation of a Celtis-specific 

exotic pest such as I: Jaava immediately prior to this decline 

episode is at least highly suspect and probably the most 

plausible primary causal agent, However, other factors, 

especially the unusual cold period in 1989, may have 

contributed to the stress on sugarberry trees which led to the 

severe dieback. A likely scenario is that the repeated 

premature defoliation, refoliation, and new sprout growth 

caused by the psyllids depleted food reserves of sugarberry 

trees and severely weakened the trees by the end of the 1989 

growing season. In late December 1989, freezing 

temperatures killed the new regrowth before it could harden 

off, further stressing the already weakened trees and 

resulting in the severe dieback episode. 

There is very little known about T. flava. As a group, the 

psyllids have been called jumping plant lice. They look very 

much like miniature cicadas and bear some resemblance to 

winged aphids. Nymphs of I: Jaava produce a white, silky 

covering over themselves rather than a leaf gall such as is 

produced by the common Pachypsylla spp. Adults of T. 

flava are greenish yellow to brown with seven small black 

spots on the thorax and a body length of 3.75 mm to 4.25 

mm from the head to the tip of the folded hyaline wings 

(Craw ford 19 14, Tuthill 1943). The insect apparently has 

two generations per year (Riemann 1958). There has been 

only one other record of T. Java in Louisiana based on a 

1979 observation in New or lean^.^ To our knowledge, it 

was not recorded again in Louisiana until the 1988-89 

outbreak. Moreover, T. flava had never been recorded in 

Mississippi until the 1989 infe~tation.~ Apparently, I: Pava 

is native neither to Louisiana nor Mississippi. Based on 

limited available literature, it appears to be native to 

southern Texas and Mexico. The insect has a very limited 

Personal communication. 1991. Joan Chapin, Entomologist, Entomology 

Department, Louisiana State Universiv, Baton Rouge, LA 70803. 

host range, feeding exclusively on Celiis species (Riemm 

1958). It has been collected only on sugarberry and netleaf 

hackbev (C. veliczrlata Torr.) from Brownsville, Ottine, 

Austin, and Marathon, TX, and has been intercepted on 

produce coming into the United States from Mexico 

(Crawford 1914, Ferris 1926, Riemann 1958, Tuthill 1943, 

Van Duzee 19 17). An important question is the mechanism 

by which the insect moved into Louisiana and Mississippi. 

Unusual climatic conditions may have allowed it to move 

northward into Texas, then along the coast for a brief period 

before being decimated by the extremely cold winter of 

1989-90. However, it seems more likely that T, Java was 

either accidentally introduced on plants or produce from 

Mexico or southern Texas, or was brought in on air currents 

from these areas. Once introduced into a new habitat with 

an abundance of susceptible sugarberry trees in southern 

Louisiana, and in the absence of natural enemies, the psyllid 

population exploded quickly and briefly before suddenly 

disappearing. Other psyllid species have caused similar 

problems on various hosts in other parts of the World. One 

example is the sudden appearance of the psyllid 

(Heteropsylla cubana Crawford) which caused widespread 

defoliation and moeaii@ of Leucaena or jumbie-bean 

[Leucaena leucocephala (Lam.) de Wit], a multipurpose 

tree on the Pacific Islands and in Southeast Asia (McFadden 

1989). 

Millions of sugarberry trees in southern Louisiana sustained 

serious dieback during the 1988-89 decline episode, 

resulting in substantial tree mortality. However, now that 

the causal agent(s) are gone, many injured trees appear to be 

recovering. Beginning in 1990, branches and trunks have 

continued to produce sprouts without repeated defoliation 

and further dieback. Immediately following the 1988-89 

damage, much of the new foliage was small and chlorotic, 

and some further dieback occurred. Since then, the new 

growth has been green, healthy, and is continuing to grow. 

Although some surviving trees that sustained serious 

dieback undoubtedly have died in the intervening years, 

most trees are expected to survive and regain vigor. Many 

trees were misshapened and developed poor growth forms, 

Perhaps most importantly over the long term is the potential 

entry of wood decay fungi at dead branch sites. Hepting 

(1971) found sugarberry to be quite susceptible to a wide 

range of wood decay fungi. Therefore, both forest stands 

and residential trees are likely to be at risk to decay for 

many years, because many wood decay fungi gain entrance 

into the bole through dead branches. 

Personal communication. 1990. Richard Brown, Entomologist, 

Entomology Department, Mississippi State University, Starkvilie, MS 

39762. 
Acknowledgments 

We thank the foltowing individuals and agencies for their 

assistance in this study: Raymond Cascon, Jr. (deceased), 

consulting forester, Port Allen, LA, for arranging study plot 

sites on Harry L. Laws & Co. lands near BrusIy, submitting 

sugarberry samples for analysis, and assistance in data 

collection; 0.E. Monier, Jr., Houma Fabricators, Inc., 

Houma, LA, for notifying us of the problem and suggesting 

that a research study be initiated to identify the cause(s), 

providing video tape of sugarberry dieback, giving 

assistance in locating plot sites on Monier lands, and 

providing observation notes on the sugarberry dieback; 

Richard Goyer and Jerry Lenhard, Entomology Department, 

Louisiana State University, Baton Rouge, LA, for assistance 

in documenting the problem, providing contacts in the 

affected area, providing photographs of adult psyllids and 

nymphs on infested foliage, and for reviewing the 

manuscript; Dale Starkey, Forest Health Protection, U.S. 

Department of Agriculture, Forest Service, Pineville, LA, 

for assistance in observing and discussing aspects of the 

problem, and for reviewing the manuscript; Richard Brown, 

Entomology Department, Mississippi State University, 

Starkville, MS, for sharing information on the psyllid 

infestation in Mississippi, providing a scanning electron 

micrograph of the psyllid nymph, and for reviewing the 

manuscript; Joan Chapin, Entomology Department, 

Louisiana State University, Baton Rouge, LA, for 

identifLing the psyllid, T. ma, and providing dates of 

previous infestations; Douglas R. Miller, U.S. Department 

of Agriculture, Agricultural Research Service, U.S. National 

Museum, Washington, DC, for confirming the identity of 

the psyllid and providing references; Don Feduccia, Olin 

Stubbs, Mike Thomas, and Burt Pope, Department of 

Louisiana Agriculhrre and Forestry, Baton Rouge, LA, and 

Clinton, MS, for assistance in locating sites for study plots 

on Gulf States Utility Go. lands near Clinton, and for putting 

us in contact with John De Marche and Ron Ard, Georgia 

Pacific Company, who facilitated the establishment of 

research plots near St. Francisville, LA.; George Miller, 

Louisiana Department of Agriculture and Forestry, 

Lafayette, LA, for assistance in delineating the western 

boundary of the sugarberry decline; Dale Pollet (Baton 

Rouge) and Severn Doughtry (Shreveport), Extension 

Entomologists, Louisiana State University, for assistance in 

documenting and verifying dates when the sugarberry 

dieback problem began; Ed Richard, U.S. Department of 

Agriculture, Agricultural Research Service, Houma, LA, for 

sharing infomation on herbicide use in sugarcane fields; 

Bruce Kirkpatrick, University of California, Davis, CA, for 

DNA probe (hybridization blot analyses) of sugarberry 

foliage for mycoplasma-like organisms; Laszlo Torma, 

Montana State University, Boseman, MT, for testing 

sugarberry samples for the presence of glyphosate 

herbicides; Glen Williams, Agronomy Department, 

Mississippi State University, Mississippi State, MS, for soil 

nutrient analyses and yhysicochernical measurements; 

Bobby McDaniel and Thad Lindsey, U.S. Department of 

Agriculture, Weather Service, Stoneville, MS, for assistance 

in compiling temperature and rainfall records; and F.I. 

McCracken, U.S. Department of Agriculture, Forest 

Service, Stoneville, MS, for making initial contacts with 

cooperators to observe the problem and for helping to 

arrange the establishment of study plots. 

This publication was produced in cooperation with the 

Mississippi Agricultural and Forestry Experiment Station 

and the Southern Hardwood Forest Research Group. 
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Mississippi Entomological Association: 3-5. 

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The use of trade or firm names in this publication is for reader information and does not imply endorsement by the 

U.S. Department of Agriculture of any product or service. 

This publication reports research involving pesticides. It does not contain recommendations for their use, nor does 

it imply that the uses discussed here have been registered. All uses of pesticides must be registered by appropriate 

State andior Federal agencies before they can be recommended. 

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife-if 

they are not handled or applied properly. Use all herbicides selectively and carefully. Follow recommended 

practices for the disposal of surplus pesticides and their containers. 
The use of trade or firm names in this publication is for reader infomation and does not 

imply endorsement by the U.S. Department of Agriculture of any product or service. 

This publication reports research involving pesticides. It does not contain 

recommendations for their use, nor does it imply that the uses discussed here have been 

registered. All uses of pesticides must be registered by appropriate State and/or Federal 

agencies before they can be recommended. 

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, 

and fish or other wildlife-if they are not handled or applied properly. Use all herbicides 

selectively and carefully. Follow recommended practices for the disposal of surplus 

pesticides and their containers. 

Solomon, J.D.; Wilson, A.D.; Leininger, T.D. [and others]. 1997. Sugarberry dieback and 

mortality in southern Louisiana: cause, impact, and prognosis. Res. Pap. SRS-9. Asheville, 

NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 16 p. 

A sudden widespread decline of sugarberry trees (Celtis laevigata) was observed in southern 

Louisiana during the period between the early fall of 1988 and spring of 1990. Approximately 

3 million acres or 5,000 square miles of forested lands were affected by the decline. In 

addition, sporadic reports of sugarberry decline also were reported at numerous locations in 

Mississippi. Investigations into the long list of potential causal agents led to the conclusion 

that the most probable causes of the darnage were due to an opportunistic exotic insect pest, 

Tetragonocephalaflava, a psyllid that caused defoliation and twig dieback, followed by a hard 

freeze which killed new regrowth following the insect damage. The psyllid has a very narrow 

host range attacking only Celtis species. Many sugarberry trees that survived the decline event 

now appear to be slowly recovering. 

Keywords: Celtis laevigata, crown dieback, episodic event, exotic pest, psyllidae, sugarberry 

decline, Tetragonocephala Java.