University of Nebraska - Lincoln
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Eastern Pine and Meadow Vole Symposia
Wildlife Damage Management, Internet Center for
2-21-1980
APPLE TREE MORTALITY, RATE AND
CAUSES
William T. Sullivan Jr.
North Carolina State University, Raleigh, North Carolina
Turner B. Sutton
North Carolina State University, Raleigh, North Carolina
Don W. Hayne
North Carolina State University, Raleigh, North Carolina
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Sullivan, William T. Jr.; Sutton, Turner B.; and Hayne, Don W., "APPLE TREE MORTALITY, RATE AND CAUSES" (1980). Eastern
Pine and Meadow Vole Symposia. Paper 19.
http://digitalcommons.unl.edu/voles/19
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APPLE TREE MORTALITY, RATE AND CAUSES
William T. Sullivan, Jr.
Turner B. Sutton
and
Don W . Hayne
North Carolina S t a t e University
Raleigh, North Carolina 27650
ABSTRACT: I n a randomly s e l e c t e d sample of 47 orchard blocks i n
Henderson County, North Carolina, over two years, the average annual
m o r t a l i t y r a t e f o r apple t r e e s was 1 . 0 percent with probably a l i t t l e
l e s s than h a l f of t h i s caused by voles.
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It i s n o t necessary t o t e l l t h i s group t h a t voles k i l l apple t r e e s ;
But t o s e t t h i s f a c t i n context, we a r e reporting on a study of t h e r a t e
and t h e causes of apple t r e e death based on observations of 28,778
t r e e s f o r t h r e e y e a r s and determination of cause of death f o r 775 t r e e s
I
This i n v e s t i g a t i o n i s p a r t of an i n t e r d i s c i p l i n a r y study being
c a r r i e d out by the North Carolina A g r i c u l t u r a l Research Service t o a s semble d a t a f o r an i n t e g r a t e d a t t a c k on the management of orchards and
orchard p e s t s i n North Carolina. This p r o j e c t (acronym:1~Oi%3)has been
described b r i e f l y t o t h i s group ( ~ a y n e1978).
METHODS: S e l e c t i o n of orchards f o r t h i s study was e f f e c t i v e l y a t
random. A few years before t h e IPOMS study began, the North Carolina
A g r i c u l t u r a l Crop Reporting Service had, f o r another purpose, photographed Henderson County from t h e a i r and outlined on a e r i a l maps a l l
of t h e obvious orchard p l a t i n g s i n Henderson County; f o r sampling purposes, they designated "blocks" which were orchard areas mostly of two
t o e i g h t a c r e s . The work a r e a s f o r t h e IPOMS study were chosen a t
random from t h e s e blocks. It was n o t possible t o e l i c i t adequate coope r a t i o n i n 23 of the 64 s e l e c t e d orchard blocks; these were eliminated.
The remaining 41 randomly s e l e c t e d blocks represent as close t o a
random s e l e c t i o n a s i s p o s s i b l e i n a p r a c t i c a l study. I n addition,
i n v e s t i g a t o r s included e i g h t blocks c a r r i e d over from other s t u d i e s ;
t h e s e perhaps were b e t t e r operated on the average. The IPOMS study i s
broad-ranging, with the dead t r e e survey being only a small p a r t . Some
r e s u l t s a r e reported h e r e from 47 orchards; i n f i v e of these only part i a l information was obtained because t h e method of t r e e s e l e c t i o n ,
p u l l i n g and examination was not acceptable t o the grower.
I n t h e blocks covered, the plan was t o p u l l and examine a l l dead
t r e e s during each of t h e t h r e e winters of 1976-77 through 1978-79.
Trees were examined i n f a l l before l e a f f a l l , when dead and dying t r e e s
could be d i s t i n g u i s h e d e a s i l y and marked. Later i n t h e winter they
were p u l l e d and t h e cause of death determined i n t h e opinion of a twoman team made up of t h e f i r s t two authors, one t r a i n e d i n w i l d l i f e and
experienced i n vole c o n t r o l and t h e o t h e r , a p l a n t p a t h o l o g i s t working
with apples.
Two kinds of information op t r e e death a r e presented here, f i r s t ,
estimates of annual m o r t a l i t y r a t e s f o r t h i s randomly s e l e c t e d sample
of orchards of Henderson County, North Carolina, and second, a percentage a l l o c a t i o n of t h e t r e e s examined t o d i f f e r e n t causes of death based
on t h e judgement of the f i e l d crew.
Calculation of mortality r a t e s i s complicated by t h e f a c t t h a t
before we s t a r t e d t o i d e n t i f y and remove t h e dead t r e e s f'rom IPOMS
orchards, not a l l the growers had removed a l l dead t r e e s every y e a r .
Therefore, i n some of the orchards (and we d i d not know which) t h e dead
t r e e s removed t h e f i r s t year were an accumulation of more than one year
of m o r t a l i t y and d i d not provide good information on t h e annual mortali t y r a t e . For t h i s reason, annual mortality r a t e s were determined only
from t h e second and t h i r d y e a r s ' r e s u l t s . We know only t o a c l o s e
approximation t h e t o t a l number of t r e e s l i v i n g and dead. A count of
t o t a l l i v i n g and dead t r e e s was made i n February 1976; dead t r e e s were
counted i n December of 1976, 1977 and 1978. During t h e following
winters the research crew pulled and examined such of these designated
t r e e s as the grower would allow. I n most but not a l l cases t h e r e was
complete agreement a s t o whether a t r e e should be pulled; with any d i s agreement t h e judgement of the grower p r e v a i l e d . I n a few cases t h e
grower p u l l e d some dead t r e e s a s r o u t i n e orchard maintenance; we bel i e v e t h a t i n most cases we know t h e number they pulled. But it may b e
t h a t the annual mortality r a t e s , calculated from t h e b e s t information
we have, may be s l i g h t l y underestimated.
The percentage d i s t r i b u t i o n of cause of death i s a summary of
f i e l d records f o r t h e 775 t r e e s examined. I n judging cause of death
t h e f i e l d crew attempted t o reach a consensus on t h e primary cause
where two o r more f a c t o r s may have had an influence. Presence of tooth
marks on bare wood of r o o t s or trunk, and t h e edge of t h e bark being i n
a d i s t i n c t l i n e a r e r e l i a b l e c r i t e r i a of vole a c t i v i t y , though not nece s s a r i l y of r e s p o n s i b i l i t y f o r death.
I n d i s t i n g u i s h i n g pine vole damage from t h a t of meadow voles, a
number of guidelines were used, and judgement was based on an evalua t i o n of both the damaged t r e e and t h e nearby vole h a b i t a t i n the
orchard. Damage t o r o o t s and g i r d l i n g from sod l i n e down i s usually
a s s o c i a t e d with pine voles whereas most meadow vole damage i s from sod
l i n e up. Pine voles seem t o begin on the r o o t s and work up. The width
of t h e g i r d l e d band i s usually g r e a t e r f o r meadow voles. Pine vole
t o o t h marks a r e s h o r t e r than those of t h e meadow vole. Pine voles make
more tunnels and holes a s compared with more surface runways f o r meadow
v o l e s . Pine voles generally do not leave grass c u t t i n g s i n the runways
but meadow voles w i l l . Pine voles w i l l leave f e c a l p e l l e t s anywhere
along t h e m a y s while meadow voles generally concentrate them a t a
few p o i n t s . Pine vole p e l l e t s a r e smaller than those of t h e meadow
vole p e l l e t s .
RESULTS: A t the f i r s t removal of dead t r e e s from these orchards,
1 . 6 percent of 28,778 t r e e s were found t o be dead and were removed.
Individual orchards v a r i e d i n incidence of dead t r e e s , from 0 t o 4.7
percent. During the second and t h i r d years of removal when t h e numbers
of dead t r e e s represented annual mortality, on t h e average 1 . 0 percent
of t r e e s were p u l l e d ( 1 . 2 percent the f i r s t year, 0.7 percent the
second) with t h i s estimate based upon 51,389 tree-years. The highest
s i n g l e value f o r annual mortality was 5.3 percent; a l l other values l a y
below 3.0 percent.
Table 1. Major causes of death of 775 apple t r e e s i n 46 Henderson
County, NC orchards; t r e e s pulled and examined during
winters of 1976-77 through 1978-79.
- -
Cause of death
Percentage d i s t r i b u t i o n
Voles
Pine voles
Meadow voles
Total, voles
38.1
3.1
Disease
Collar r o t
White r o o t r o t
Clitocybe
Armillaria
Black r o o t r o t
Root r o t (undetermined)
Union necrosis (TRSV)
Total, disease
13.9
9.9
3.2
1.8
0.3
7.5
0.3
Other i d e n t i f i e d causes
Winter injury
TOP injury
Mechanical injury
Drowning
Roundheaded apple borer
Wooly aphid
Total, other
Unknown causes
1.7
2 .8
2.3
4.8
1.0
0.3
12.9
9 0
Cause of death was determined f o r a t o t a l of 775 t r e e s with allocat i o n t o t h e various i d e n t i f i e d causes a s shown i n Table 1. The pine
vole was by f a r t h e most important single cause of death i d e n t i f i e d ,
although the two species of voles together accounted f o r l e s s than half
the mortality. A l l diseases together were s l i g h t l y l e s s important than
t h e pine vole.
DISCUSSION: This study suggests t h a t only about 40 percent of
these deaths of apple t r e e s i n Henderson County were caused by voles.
Although t h i s was an important l o s s , it was exceeded by other causes of
death. On the average, the annual mortality r a t e of t r e e s was about 1
percent, thus t h e average annual l o s s t o voles was l e s s than 0.5 percent. Higher l o s s e s , however, were concentrated i n r e l a t i v e l y few
orchards; we recorded one value of 5.7 percent: we may expect t h a t
more extreme values would be found i f more orchards were studied.
We recognize t h a t the causes of mortality assigned here were not
independent and t h a t the death of any one t r e e may have resulted from
t h e combined a c t i o n of several f a c t o r s . I n p a r t i c u l a r , an i n t e r a c t i o n
between vole damage and various root diseases seems t o be a good possib i l i t y and perhaps an important f a c t o r of mortality. What r o l e does the
vole p l a y i n providing a wound through which the t r e e may become i n f e c t e d with disease? Does t h e presence of root disease increase or
decrease damage by voles?
LITERATURJ3 CITED
.
.
Hayne, D W . 1978. 1976 IWMS vole r e s u l t s . pp 40-48
Proc . Second
Eastern Pine and Meadow Vole Symposium, B e l t s v i l l e , MD: 110 pp.