In cooperation with Illinois State Natural History Survey.Cover title

Gannon, Norman

Luckman, W.H.

Petty, Howard Bliss

IDEALS @ Illinois

Controlling earworms on sweet corn

Illinois Digital Environment for Access to Learning and Scholarship Repository

Contro~-g-~~~A~TI:~NG~C~OP-Y~ 

TU ·E LIBRAR~ 

EARWORMS on 

SWEET CORN 

By Norman Gannon 
W. H. Luckmann 
and 
H. B. Petty 
TING COPY-
Circular 739 
UNIVERSITY OF ILLINOIS 
(OllEGE OF AGRICULTURE 
Extension Servi(e in Agriw[ture 
and Home E(onomiu 
in cooperation with 
ILLINOIS STATE NATURAL HISTORY 
SURVEY 
T H E  C O R N  E A R W O R M ,  k n o w n  a l s o  a s  t h e  
t o m a t o  f r u i t w o r m  a n d  t h e  b o l l w o r m ,  a t t a c k s  
m a n y  c u l t i v a t e d  c r o p s .  I t  i s  a  s e r i o u s  p e s t  o f  
f i e l d  c o r n  t h r o u g h o u t  t h e  w o r l d  a n d  o n e  o f  t h e  
m o s t  i m p o r t a n t  s w e e t  c o r n  p e s t s  i n  I l l i n o i s .  
S w e e t  c o r n  g r o w e r s  s h o u l d  t h e r e f o r e  k n o w  h o w  
t o  r e c o g n i z e  a n d  c o n t r o l  e a r w o r m .  
L i f e  h i s t o r y  o f  t h e  e a r w o r m  
T h e  l i f e  h i s t o r y  o f  t h e  c o r n  e a r w o r m  i s  s i m i l a r  
t o  t h a t  o f  a n y  o t h e r  m o t h  o r  b u t t e r f l y .  T h e  i n s e c t  
g o e s  t h r o u g h  f o u r  s t a g e s  o f  d e v e l o p m e n t  - e g g ,  
w o r m ,  p u p a ,  a n d  m o t h .  A  f e m a l e  m o t h  l a y s  a s  
m a n y  a s  2 , 0 0 0  e g g s  w h i c h  h a t c h  i n  2  t o  5  d a y s  a s  
t i n y  w o r m s  o r  l a r v a e .  T h e s e  l i t t l e  w o r m s  f o l l o w  
t h e  s i l k s  i n t o  t h e  e a r  a n d  f e e d  t h e r e .  W h e n  t h e  
w o r m s  b e c o m e  f u l l  g r o w n ,  t h e y  l e a v e  t h e  e a r ,  g o  
i n t o  t h e  g r o u n d ,  a n d  b e c o m e  p u p a e  ( c o c o o n s ) .  
A f t e r  s o m e  t i m e ,  t h e  m o t h s  e m e r g e  f r o m  t h e  
c o c o o n s .  D e v e l o p m e n t  f r o m  e g g  t o  a d u l t  t a k e s  
a b o u t  3 0  d a y s .  
W h e n  t h e  e g g s  a r e  l a i d  
I n  s o u t h e r n  I l l i n o i s  m o t h s  l a y  e g g s  f r o m  m i d ­
s p r i n g  u n t i l  f r o s t .  I n  n o r t h e r n  I l l i n o i s ,  e g g s  f i r s t  
a p p e a r  i n  J u n e .  E g g - l a y i n g  o f  t h e  s e c o n d  g e n e r a ­
t i o n  b e g i n s  i n  l a t e  J u l y  a n d  c o n t i n u e s  u n t i l  f r o s t .  
M o s t  o f  t h e  e g g s  a r e  l a i d  o n  f r e s h  s i l k s ,  a l t h o u g h  
b e f o r e  s i l k s  a p p e a r  
t h e y  m a y  b e  l a i d  
o n  a n y  p a r t  o f  t h e  
c o r n  p l a n t .  T h e n  
t h e  y o u n g  w o r m s  
f e e d  o n  t h e  s t a l k  
a n d  t a s s e l .  A f t e r  
t h e  s i l k s  a r e  d r y ,  
m o t h s  m a y  c o n ­
t i n u e  t o  l a y  e g g s  
o n  o r  a b o u t  t h e  
e a r s .  
F o u r  e a r w o r m  e g g s  o n  

c o r n  s i l k s .  P e n c i l  p o i n t s  

t o  e g g  a t  t o p .  E g g s  

p i c t u r e d  a b o u t  4  t i m e s  

a c t u a l  s i z e .  

When insecticides should be applied 
The first application, which is very important, 
should be made when about 20 percent of the ears 
in the field show fresh silks. The crop must be 
sprayed every 3 to 5 days until two to four, pos­
sibly even five, applica­
tions have been made. 
The object is to keep the 
silks covered with insec­
ticide. 
The number of appli­
cations depends on how 
long egg-laying lasts and 
how intense it is, how 
uniformly the ears silk, 
and how valuable the 
crop is. Most canning 
corn in Illinois can be 
protected by two or three 
sprayings, but market 
corn may need three to 
five. The very early fields 
Mature earworm in tassel. 
About natural size. in central and southern 
Illinois and the very late 
fields throughout Illinois generally need extra 
protection. 
Space treatments 5 days apart when the weather 
is cool and silking is slow. When the weather is 
warm and the silks are developing fast, shorten 
the time between sprayings. When infestations 
occur before the ears are in silk and if more than 
20 percent of the plants are infested, spray 
promptly. 
Recommended insecticides and equipment 
The most effective earworm insecticide is DDT 
applied at the rate of 17'2 pounds to the acre. To 
spray an acre, mix 3 quarts of 25-percent DDT 
emulsion concentrate with 27'2 gallons of a highly 
refined horticultural oil of a mineral type (vis­
cosity 45 to 90 Saybolt). Then add enough water 
to make 25 gallons of spray. 
A high-clearance, self-propelled sprayer that 
can maintain 50 to 150 pounds of pressure with 
all its nozzles in operation is recommended. Con­
stant mechanical agitation of the spray solution is abso­
l u t e l y  n e c e s s a r y .  T h e  m a c h i n e  s h o u l d  b e  e q u i p p e d  
w i t h  4  t o  6  n o z z l e s  p e r  r o w ,  p r e f e r a b l y  3  n o z z l e s  
o n  e a c h  s i d e  o f  t h e  r o w .  T h e  n o z z l e s  s h o u l d  b e  d i · ·  
r e c t e d  a t  t h e  e a r  z o n e .  T h e  s p r a y e r  "drop~ s h o u l d  
b e  f a i r l y  r i g i d .  A  c o i l  s p r i n g  a t t a c h e d  w h e r e  t h e  
d r o p  a n d  t h e  b o o m  j o i n  w i l l  k e e p  t h e  d r o I ' s  f r o m  
b r e a k i n g .  
H i n t s  o n  p l a n t i n g  p r a c t i c e s  
C o r n  t h a t  m a t u r e s  i n  m i d s e a s o n  i s  m o r e  a p t  t o  
b e  f r e e  f r o m  t h e  a t t a c k  o f  e a r w o r m s  t h a n  c o r n  t h a t  
m a t u r e s  e a r l y  o r  l a t e .  I n f e s t a t i o n s  i n  e a r l y  c o r n  
a r e  e a s i e r  t o  c o n t r o l  t h a n  t h o s e  i n  l a t e  c o r n .  I n
~ 
' \  
s o u t h e r n  I l l i n o i s ,  e a r w o r m s  u s u a l l y  c o m p l e t e l y  d e ­
r  
s t r o y  l a t e  p l a n t i n g s  o f  s w e e t  c o r n  a n d  t h e  c o s t  o f  
t  
p r o t e c t i n g  t h e  c r o p  i s  p r o h i b i t i v e .  M o s t  I l l i n o i s  
t  
g r o w e r s  o f  c a n n i n g  c o r n  w i l l  b e  w i s e  t o  q u i t  p l a n t ­
v  
i n g  c o r n  t h a t  m a t u r e s  m u c h  a f t e r  S e p t e m b e r  1 .  
i l  
S i n c e  e a r w o r m s  o n  C o u n t r y  G e n t l e m a n  s w e e t  
j  
c o r n  a r e  v e r y  h a r d  t o  c o n t r o l ,  t h i s  v a r i e t y  s h o u l d  
c  
b e  p l a n t e d  e a r l y  t o  m i s s  t h e  h e a v y  e g g - l a y i n g  o f  
a  
t h e  l a t e  s e a s o n .  
S a t i s f a c t o r y  a n d  e c o n o m i c a l  c o n t r o l  o f  e a r ­
\ I  	
w o r m s  c a n n o t  b e  o b t a i n e d  i n  a n y  f i e l d  u n l e s s  t h e  
e a r s  m a t u r e  u n i f o r m l y .  G o o d  f a r m  p r a c t i c e s  i n  
s e l e c t i n g  s e e d ,  a p p l y i n g  f e r t i l i z e r ,  a n d  p l a n t i n g
s  	
h e l p  t o  a s s u r e  c o n t r o l .  
a  
t ;  
b  
t ]  
E U R O P E A N  C O R N  B O R E R S  a n d  c o r n  
o  
e a r w o r m s  o f t e n  a t t a c k  t h e  c o r n  p l a n t  
C~ 
a t  t h e  s a m e  t i m e .  S p r a y s  a p p l i e d  f o r  
t 1  
c o n t r o l  o f  e a r w o r m s  w i l l  a l s o  c o n t r o l  
f c :  
c o r n  b o r e r s  a l t h o u g h  o n e  o r  t w o  t r e a t ­
a ]  
m e n t s  b e f o r e  t h e  c o r n  s i l k s  w i l l  u s u a l l y  
b e  n e c e s s a r y  t o  p r o t e c t  s w e e t  c o r n  h o m
t l  

m  
t h e  a t t a d <  o f  c o r n  b o r e r s .  

t i  
0 ]  
e c  
F;  	
M a r c h , 1 9 5 5  
U r b a n a ,  I l l i n o i  
c o  	
C o o p e r a t i v e  E x t e n s i o n  \ V o r k  i n  A g r i c u l t u r e  a n d  H o m e  E c o n o m i c s :  U n  
v e r s i t y  o f  I l l i n o i s ,  C o l l e g e  o f  A g r i c u l t u r e ,  a n d  t h e  U n i t e d  S t a t e s  ] ) e p a r '  
t o  
m e n t  o f  A g r i c u l t u r e  c o o p e r a t i n g .  L O U I S  n .  H O W A R D ,  D i r e c t o r .  A c t  
p i c  
a p p r o v e d  b y  C o n g r e s s  l \ I a y  8  a n e l  J u n e  3 0 ,  1 9 1  . . .  
a c  
1 0 : ' 1 - 3 - 5 5 - 5 7 0 2  


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Controlling earworms on sweet corn

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