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Sweet Corn Pheromone Trap Network for Western New York, 2001

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 9.18.01

ECB-E and Z catches are mostly low this week, with the exception of a little blip in the E race catch in Rush. FAW and CEW catches are not high in as many areas as last week. This may reflect the fact that fields near the traps are less attractive as silks dry down. Where CEW trap catches have been high in previous weeks it's important to adhere to the spray intervals in the table below for any fields still in the green silk stage. The latest maturing fields are very attractive for egg-laying because all of the other corn in the area has dried down. The spray intervals recommended for CEW will also provide good control of ECB and FAW.

Corn should be first scouted for ECB and common armyworms and fall armyworms at early tassel emergence. This year with the heavy common armyworm populations, keep an eye on whorl stage fields for the ragged feeding damage typical of armyworms. 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 whorl 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. 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 count.

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 there.

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:

AverageCEW 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.

Map with sweet corn pheromone trap catches in NY, PA, NJ, and MD

The numbers below are the weekly total for each location.

Location

ECB-E

ECB-Z

FAW

CEW

Baldwinsville (Onondaga Co.)

0

1

0

6

Eden H (Erie Co.)

0

0

--

--

Eden Z (Erie Co.)

--

1

9

34

Farmington (Ontario Co.)

3

0

0

0

Hall (Ontario Co.)

0

0

4

4

Hamlin (Monroe Co.)

1

2

9

161

Kennedy (Chautauqua Co.)

0

7

1

2

King Ferry (Cayuga Co.)

0

0

43

17

Kirkville (Madison Co.)

NA

NA

NA

NA

LeRoy (Genesee Co.)

0

0

8

--

Lockport (Niagara Co.)

0

--

--

1

Medina (Orleans Co.)

0

1

1

4

Owego J (Tioga Co.)

no more reports from this location

Owego W (Tioga Co.)

NA

NA

NA

NA

Penn Yan (Yates Co.)

2

0

0

1

Rush (Monroe Co.)

17

3

6

5

Spencerport (Monroe Co.)

1

6

1

8

Williamson (Wayne Co.)

1

2

1

1