No. 106 

1960 

SWEETGUM BLIGHT AND DIEBACK OF ASSOCIATED HARDWOODS 

ON THE BELTSVILLE EXPERIMENTAL FOREST IN MARYLAND 

In 1948, a dieback of sweetgum (Liquidambar styraciflua L.) was first observed and reported at College Park, 

Md. 1 Since then, surveys made from Maryland southward have 

shown that the dieback, now termed sweetgum blight, has increased in both distribution and severity and now occurs 

throughout much of the species' range. No pathogenic organism has been found to be associated with this blight. 

At the Beltsville Experimental Forest, which is less 

than 10 miles from College Park, a detailed evaluation of 

this disease was made in July 1959 on a 33-acre compartment. 

All sweetgums and other principal hardwoods, predominately 

oaks, were examined for crown dieback. A classification of 

affected crowns developed by ~oole~ was used. It is as follows : 

Crown dieback Portion of 

index value crown affected 

None 

Up to 1/8 

1/8 to 1/2 

Over half 

Dead trees 

This inventory was based on forest types. When the 

data were summarized, two facts stood out: (1) Nearly half 

the sweetgums, all of which were growing on sites unaffected 

l~iller, P. R., and U'Brien, M. J. An apparently new sweetgum disease in 

Maryland. U.S. Dept. Agr. Plant Dis. Rptr. 35: 295-297, 1948. 

'~oole, E. Richard, and Broadfoot, W. M. Sweetgum blight as related to alluvial soils of the Mississippi flood plain. Forest Sci. 5: 2-9, illus. 1959. 
by influences such as highways, drainage ditches, habi tations, and similar disturbances, exhibited typical blight 

symptoms. (2) Relatively few of the associated hardwoods 

showed crown deficiencies--in fact, more than 90 percent of 

them had sound, healthy crowns. 

The three forest types on which the inventory and 

dieback tally was based were pine, pine-hardwood, and mixed 

hardwoods. The areas of these were 12.7, 12.9, and 7.2 

acres respectively. Within these types the proportion of 

sweetgum trees affected with blight was: pine type, 56 percent; pine-hardwoods, 53 percent ; and mixed hardwoods, 37 

percent. In all, 517 sweetgums, ranging from 5 to 21 inches 

d.b.h.,were examined, of which 48.4 percent were affected. 

This compared very unfavorably wi th the associated 

hardwoods. Out of 2,102 hardwood trees examined (red or 

white oaks, and a few maples and black gums), less than 8 

percent were classed as showing some form of top dieback 

(fig, 1) Further, it is not believed this condition was 

necessarily pathogenic in these species; more likely it was 

Figure 1.--A white oak showing typical crown dieback. 

This tree was assigned a crown index value of 4. 
Figure 2. --A group of po le-size sweetgums showing advanced 

blight symptoms. A few larger healthy gums are visible. 

simply a manifestation of overmaturity, decadence, or suppression. In contrast, the affected sweetgums exhibited the 

typical blight characteristics (fig. 2) described by others .' 

Figure 3 portrays the distribution of tree crown conditions for species, by index values and by forest types. 

From this it is very evident that the frequency of crown 

deterioration in sweetgum greatly exceeds that in the other 

hardwoods. In fact, the prevalence of this condition is 6 

times greater in the sweetgum--48 percent compared to 8 percent when all trees are considered. 

On the other hand, figure 3 shows some indication 

that, as dieback severity increases, the number of sweetgums 

affected tends to decrease. The reverse is generally true 

of the other hardwoods. 

In 1954, a survey covering all the Atlantic and Gulf 

Coast States from Delaware to Louisiana was made by ~e~tin~.~ 

The condition of the crowns of sweetgums and associated 

3~ller, P. R., and Gravatt, G. F. The sweetgum blight. U. S. Dept. Agr. 

Plant Dis. Rptr. 36: 247-252, 1952. 

4~epting, G. H. A southwide survey of sweetgum blight. U. S. Dept. Agr. 

Plant Dis. Rptr. 39: 261-265, 1955. 
CROWN DIEBACK INDEX 

Figure 3. --Distribution of crown-dieback classes 

within forest-type groups. 

hardwoods was recorded by classes regardless of possible 

causes of the condition. His findings were not unlike those 

reported in this paper. About one-third of all sweetgums 

examined were affected with some degree of dieback; and in 

the white and red oak groups combined, approximately 12 percent showed crown deficiencies. 

These observations indicate that sweetgum blight-- 

whatever causes it--is potentially a serious threat to the 

sweetgums in southern forests. 

--R. H. FENTON and J. D. DILLER 

Laurel Research Center 

Northeastern Forest Experiment Station 

Forest Service, U. S. Dept . Agriculture