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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 7.12.01

ECB-E catches remain low throughout the area. ECB-Z catches are mostly going down in the western part of the trapping area and staying about the same or increasing in the eastern part of the area. The western area has mostly the two generation Z race and the eastern area (from about Rochester east) has the one generation race in addition. So in the eastern part of the area Z trap catches will probably be on the increase and in the western area they will probably continue to decrease. CEW were caught in low numbers this week in Lockport and Medina. I found large common armyworms in a silk stage corn field last week. It looked more like the eggs had been laid in the corn field rather than the invasions we've been hearing about. The infestation was spotty and not concentrated at the edges of the field.

Watch for common armyworm migrating from small grain or grass hay fields into corn and other vegetable crops. I've heard about them marching across roads in large numbers, and infesting peppers, strawberries, and lawns in addition to corn. If they are a problem in sweet corn, the 15% infested plants threshold applies for pre-tassel corn, and 5% for silk stage corn. Scout fields even if they are not at the tassel emergence stage, especially if small grain or grass cover crop or hay fields are nearby. Photo of a common armyworm larva: http://www.ag.ohio-state.edu/~ohioline/icm-fact/images/105.html

Corn should be first scouted for ECB and common and fall armyworms at early tassel emergence. This year with the heavy common armyworm populations, keep an eye on whorl stage fields for invasions from adjacent fields. 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 showing 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.

Link to ECB photos: http://www.nysaes.cornell.edu/ent/factsheets/pests/ecb.html

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

7-9

1 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.

Link to CEW photos: http://www.nysaes.cornell.edu/ent/factsheets/pests/cew.html

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

CEW

Batavia (Genesee Co.)

0

0

--

Baldwinsville (Onondaga Co.)

0

4

--

Eden H (Erie Co.)

1

8

--

Eden Z (Erie Co.)

--

4

0

Farmington (Ontario Co.)

0

15

--

Hall (Ontario Co.)

0

4

--

Hamlin (Monroe Co.)

0

11

0

Holly (Orleans Co.)

2

7

--

Kennedy (Chautauqua Co.)

2

15

--

King Ferry (Cayuga Co.)

0

18

0

Kirkville (Madison Co.)

0

12

0

LeRoy (Genesee Co.)

0

0

0

Lockport (Niagara Co.)

1

0

3

Medina (Orleans Co.)

0

1

1

Owego (Tioga Co.)

0

1

--

Penn Yan (Yates Co.)

0

6

--

Rush (Monroe Co.)

0

14

0

Spencerport (Monroe Co.)

1

10

0

Williamson (Wayne Co.)

1

9

0