2007 Extension Research Report
Insect Management
EFFICACY OF REGISTERED INSECTICIDE CHEMISTRIES FOR
CONTROL OF CORN EARWORM IN SILKING SWEET CORN
Alton N. Sparks, Jr., University of Georgia Cooperative Extension, Department of Entomology,
Tifton, GA 31793, asparks@uga.edu
replications. The entire test area was treated
during the whorl stage with novaluron (Rimon,
Crompton) to protect the test from a whorl stage
infestation of fall armyworm.
The insecticides evaluated included a
representative pyrethroid insecticide (Warrior
1SC at 3.84 oz/ac), Lannate 2.4EC at 1.5 pints/ac
(one of the two carbamate insecticides registered
for sweet corn), and SpinTor 2SC at 6 oz/ac.
These insecticide treatments were applied on
Mondays, Wednesdays and Fridays, starting at
first detection of silk emergence with the last
application three days before harvest. Application
dates were 2, 4, 6, 9, 11, 13, 16, 18, and 20 Oct.
Plots were harvested and rated on 23 Oct.
Treatments were applied with a CO2 pressurized
backpack sprayer (60 PSI) in a total volume of 30
gpa. A single ‘drop’ boom was used between
adjacent rows of a plot with two hollow cone
nozzles pointed at the ‘ear zone’ of each row. The
boom was carried between rows of the plot such
that the two middle rows were sprayed from each
side and the outside rows were treated only from
the inside of the plot.
At harvest maturity, 25 ears were
harvested from the middle two rows of each plot
and examined for damage by caterpillars and
presence of caterpillars. Each ear was rated for tip
damage on a 0 to 3 scale as follows: 0 = no
damage at the tip of the ear (referred to as none),
1 = less than 5 kernels damaged at the tip (referred
to as light damage), 2 = greater than 5 kernels
damaged but damage restricted to the outer one
inch of the ear (referred to as tip damage), 3 =
damage extending from the tip down greater than
one inch (referred to as ear damage). Ears were
also examined for damage originating lower on
the ear (probably from fall armyworm) and scored
Introduction
While sweet corn has a variety of pests
that attack the crop, the most consistent pest of
sweet corn is the corn earworm. While this pest
can attack the crop throughout most of the
growing season, it is primarily of concern as a
direct pest of corn ears. Once silk emergence
begins, moths will lay eggs on the silks of the
ears. The emerging caterpillars feed down the
silks to the tip of the ears where they continue to
feed and complete there larval development. The
damage by these larvae generally make infested
ears unmarketable. When populations of earworm
are moderate to high, prevention of this damage
requires frequent insecticide applications from
silk emergence until harvest. Typically, the
pyrethroid insecticides are relied upon heavily for
control of this pest because of their cost-effective
efficacy and applicator safety. However, in the
past two years, there have been concerns with
potential resistance to the pyrethroid insecticides.
There are very limited registered alternatives to
the pyrethoid insecticides at this time. This test
was conducted to evaluate the efficacy of the
registered insecticide chemistires against corn
earworm in sweet corn.
Materials and Methods
A small plot efficacy trials was conducted
at the University of Georgia’s Tifton Vegetable
Park. Sweet corn, var. Serendipity, was direct
seeded on 18 Aug., 2006. While most of
Georgia’s sweet corn production occurs in the
Spring, this trial was conducted in the Fall as pest
pressure is generally greater. The crop was
planted on 36 inch rows, with experimental plots
measuring four rows by 23 feet arranged in a
randomized complete block design with four
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as damage present or absence (referred to as side
damage). Any caterpillars present in the ears were
identified, classified as small (< 1/4 in), medium
(1/4 to ½ in) or large (> ½ in), and counted. All
data were analyzed with the PROC ANOVA
procedure of PC-SAS. Where significant
differences were detected (P<0.05), means were
separated with LSD (P=0.05).
normally approaches 100 percent damage, while
in this test the non-treated control had 55% of ears
rated with tip or ear damage (Table1). All
insecticides tested provided similar prevention of
tip damage (primarily corn earworm) and side
damage (primarily fall armyworm) (Table 1), and
control of both corn earworm (Table 2) and fall
armyworm (Table 3). It is of interest that the
Warrior treatment had no corn earworm larvae at
harvest, indicating that resistance to the pyrethroid
insecticides was not of concern in this population.
Results and Discussion
Pest pressure was moderate in this test.
Under heavy pest pressure, the non-treated control
Table 1. Damage incidence in corn ears at harvest, sweet corn efficacy study, Tifton Vegetable
Park, Tifton, Georgia, 2006.
Number of ears (of 25) rated in tip damage category
Treatment
Tip damage
Ear damage
Tip or ear
damage
No. of ears
with ‘side’
damage
None
Light
Check
10.00 b
1.25 a
8.50 a
5.25 a
13.75 a
3.00 a
SpinTor
21.75 a
0.50 a
1.75 b
1.00 b
2.75 b
0.00 b
Lannate
23.25 a
0.50 a
1.25 b
0.00 b
1.25 b
1.00 b
Warrior
24.00 a
0.25 a
0.25 b
0.50 b
0.75 b
1.00 b
Numbers within columns followed by the same letter are not significantly different (LSD; P=0.05).
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Table 2. Corn earworm ear infestations at harvest, sweet corn efficacy study, Tifton Vegetable
Park, Tifton, Georgia, 2006.
Number of CEW larvae per 25 ears
Treatment
Small
Medium
Large
Total
Check
4.00 a
6.75 a
4.00 a
14.75 a
SpinTor
0.00 a
0.75 b
0.00 b
0.75 b
Lannate
0.25 a
0.75 b
0.00 b
1.00 b
Warrior
0.00 a
0.00 b
0.00 b
0.00 b
Numbers within columns followed by the same letter are not significantly different (LSD; P=0.05).
Table 3. Fall armyworm ear infestations at harvest, sweet corn efficacy study, Tifton Vegetable
Park, Tifton, Georgia, 2006.
Number of FAW larvae per 25 ears
Treatment
small
Medium
Large
Total
Check
1.75 a
4.25 a
0.75 a
6.75 a
SpinTor
0.00 b
0.00 b
0.00 a
0.00 b
Lannate
0.50 b
0.00 b
0.00 a
0.50 b
Warrior
0.00 b
0.25 b
0.50 a
0.75 b
Numbers within columns followed by the same letter are not significantly different (LSD; P=0.05).
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