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Sweet Corn Pheromone Trap Network for Western New York, 2002

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 9/03/02

The ECB flight is generally down this week with the notable exception of the Z race catch in Rush. CEW trap catches are not at the high levels we were seeing at some locations last week but are still high enough to warrant close attention to recommended spray intervals in green silk stage fields. As the season winds down and there are fewer corn fields left, CEW pressure may be higher than expected based on the state of silks. Without very attractive fields available moths may lay their eggs in fields with drier silk. Remember that larvae laid within week of harvest will not be hatched or will be barely visible at harvest so fields do not need to be sprayed if harvest will be finished within a week and control was good up to then. The spray interval recommended for CEW will also take care of any ECB or FAW infestations. See information below on using CEW trap catches to schedule insecticide applications in green silk stage fields. FAW trap catches are still high at several locations.

Corn should be first scouted for ECB, armyworms, and CEW larvae where they are being caught, at early tassel emergence. Even at a location with high ECB populations, insecticide applications to whorl stage corn did not result in improved control when compared with one or two well-timed applications at tassel emergence. Larvae feeding in the whorl are protected from insecticide applications and mortality will not be as high as at tassel emergence, when larvae feeding in the emerging tassel are exposed to the spray. Larvae will leave the tassel as it opens up and no longer provides a moist, protected feeding environment, and move down the plant looking for protected places to feed. Insecticide applications need to be timed to kill larvae before they bore into a new feeding location where they will be again protected from sprays. In fields with uneven development, two applications may be necessary, one when approximately 25-50% if the tassels have emerged, and again after 75% of the tassels have emerged, if the field is still over threshold.

The threshold for ECB and armyworms at tassel emergence is 15% infested plants. For corn borers, look down into emerging tassels for tiny larvae or frass (white to brown material about the size of fine sand). For armyworms look for ragged feeding holes and frass pellets the texture of coarse sawdust. The North Carolina web page cited above describes CEW whorl feeding as follows: numerous ragged holes appear when the blades unfurl. Wet, tan to brown excrement lodges in the whorl and blade axils. This condition is often referred to as "shatterworm" injury.

Before any insecticides have been applied, scouting is fast and easy because any sign of feeding is an almost sure sign of live larvae, so it's not necessary to spend time finding the larvae. After the initial insecticide application, feeding damage may be from a larva that has already been killed, so finding the critter is more important for an accurate estimate of the number of infested plants.

Once a field is silking, the threshold drops to 5% infested plants. Scout the ear zone (roughly from two leaves above and one leaf below the ears) for egg masses and 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 80F for the previous 2-3 days.

Maps of sweet corn pheromone trap catches for several states can be found at the Northeast Pest Watch Monitoring Network web site.

Location

ECB-E

ECB-Z

CEW

FAW

Baldwinsville (Onondaga)

NA

NA

NA

NA

Batavia (Genesee Co.)

NA

NA

NA

NA

Eden H (Erie Co.)

5

19

--

--

Eden Z (Erie Co.)

6

22

56

11

Farmington (Ontario Co.)

4

8

4

3

Hall (Ontario Co.)

1

2

10

150

Hamlin (Monroe)

2

40

8

12

Kennedy (Chautauqua Co.)

NA

NA

NA

NA

King Ferry (Cayuga)

0

5

67

7

Kirkville (Madison)

NA

NA

NA

NA

LeRoy (Genesee Co.)

NA

NA

NA

NA

Lockport (Niagara Co.)

2

3

66

2

Medina (Orleans Co.)

NA

NA

NA

NA

Owego (Tioga)

7

27

36

330

Penn Yan (Yates Co.)

0

5

4

23

Rush (Monroe Co.)

16

175

22

14

Spencerport (Monroe Co.)

4

16

54

--

Williamson (Wayne Co.)

2

15

34

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