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Sweet Corn Pheromone Trap Network

for Western NY - 2008

This is a seasonal scouting report giving growers in the Western New York area information on the presence of sweet corn pests and recommendations on scouting and thresholds. The report is written by Abby Seaman, NYS IPM's Area Extension Educator for Vegetables.

For 9/2/08

Both E and Z race European corn borer catches continue on a mostly downward trend, with most locations in the single digits this week.  Corn earworm are being caught at most locations at this point, with catches remaining in the single digits at most locations.  There are a couple of locations with catches high enough for a 4 day spray interval, though.  With fewer and fewer fields in the green silk stage, earworm pressure is likely to increase in the latest planted fields.  I saw fields today that are at least 3 weeks from harvest, giving larvae time to get big and ugly, and do a lot of damage if not treated.  Fields within a week of harvest do not need additional sprays.  Newly hatched larvae will be very small and not noticeable to the consumer.  Fall armyworm were not caught at any trap sites this week.

Once a field reaches the silk stage, the threshold drops to 5% infested plants. Scout the ear zone (roughly from two leaves above and one leaf below the ears) for ECB egg masses and ECB or FAW larvae.  Egg masses are found most frequently on the underside of leaves near the midrib, and consist of approximately 10-20 flattened eggs overlapping like fish scales. Eggs are white when first laid, turning cream colored after a couple of days, and show the black head capsules of the tiny larvae through the surface of the eggs when within 1 day of hatching (the "black head" stage).  Egg masses can also sometimes be found on the flag leaves of the ears or on the husk itself.  Eggs take approximately 100 base 50 degree days to hatch.   When temperatures are in the 70's during the day and the 50's at night egg masses will take about a week to hatch.  When temperatures are in the 80's during the day and the 60's at night, they could hatch in only 4 days.

Look down into the tops of the silks for newly hatched larvae, and pull the ear away from the stalk slightly to look for larvae feeding between the stalk and the ear.

Once CEW are being caught in higher numbers, insecticide applications in silk stage fields should be determined by CEW trap catches.  The recommended spray intervals for CEW should be adequate for ECB and FAW control.  Because CEW lay their eggs directly on the silk, and eggs are difficult to find in the field unless the population is VERY high, we rely on pheromone trap catches rather than scouting to make CEW management decisions.  It is most important to adhere to the recommended spray intervals when the field is in the green silk stage.  The chart below indicates recommended spray intervals during the silk stage for a range of trap catches:

Average CEW Pheromone Trap Catches

Per Day
Per Five Days
Per Week
Days Between Sprays
<0.2
<1.0
<1.4
No Spray (for CEW)
0.2-0.5
1.0-2.5
1.4-3.5
6 days
0.5-1.0
2.5-5.0
3.5-7.0
5 days
1-13
5-65
7-91
4 days
over 13
over 65
over 91
3 days
Add one day to the recommended spray interval if daily maximum temperatures are less than 80 F for the previous 2-3 days.

Location
ECB-E
ECB-Z
CEW
FAW
Adams Center (Jefferson Co.)
NA
NA
NA
NA
Auburn (Cayuga Co.)
NA
NA
NA
NA
Baldwinsville (Onondaga Co.)
12
0
9
0
Batavia (Genesee Co.)
2
6
0
NA
Bellona (Yates Co.)
0
3
31
0
Conewango Valley (Cattaraugus Co.)
NA
NA
NA
NA
Eden Z (Erie Co.)
2
5
3
0
Farmington (Ontario Co.)
1
7
7
0
Hamlin (Monroe Co.)
0
12
15
0
Kennedy (Chautauqua Co.)
1
2
2
0
King Ferry (Cayuga Co.)
NA
NA
NA
NA
Kirkville (Madison Co.)
NA
NA
NA
NA
LeRoy (Genesee Co.)
4
NA
6
NA
Lockport (Niagara Co.)
0
2
3
0
Medina (Orleans Co.)
NA
8
0
0
Owego (Tioga Co.)
NA
NA
NA
NA
Penn Yan (Yates Co.)
4
5
6
0
Spencerport (Monroe Co.)
2
4
4
0
Wayland (Steuben Co.)
NA
NA
NA
NA
Williamson (Wayne Co.)
0
2
0
0