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ISSUE 8  June 25, 1998

 

START SCOUTING FOR WHEAT MIDGE

    Orange wheat blossom midge emergence is underway in the eastern counties. As you move west and north, emergence of females will begin by the end of this week, or June 27. For counties to the far north, Cavalier, Bottineau, Rollette, Burke, Renville, and northern Towner, female midge emergence is expected closer to July 2.

Dates When Female Wheat Midge Emergence Begin

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    In many of the eastern and central counties, detections of adults should be possible, now. The males are the first to begin emerging. Some of the first reports are coming in to offices now. Ken Nichols, Extension Agent in Grand Forks Co., reported midge were observed in very low numbers the weekend of June 20-21.

    Here in the Fargo area, numbers of overwintering midge are lower, and with the less than favorable weather conditions in the evening, detections have yet to be made. But, in Richland county, the degree days are at 1450, so peak emergence is occurring.

    As a reminder, the decision to treat wheat for midge should be determined by growth stage and the number of midge found on wheat heads during evening scouting activities. One midge per 4 to 5 wheat heads during head emergence to early flowering is the treatment guideline.

    As reported last week, the "lauxanid" fly, which has a plump body and is tan in color, compared to the wheat midge, which has a slender body and is bright orange, are present in the fields. So, be sure people aren't seeing Lauxanids and thinking wheat midge.

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    There have been questions about tank mixing a fungicide with the Lorsban 4E-SG. Dow Agrosciences representatives informed me that compatibility should not be a problem with the wheat fungicides. They did recommend that the Lorsban be added to the spray tank last for best mixing results.

 

Wheat Midge DD Accumulations (Base 40F)*

Location

6/23/97

Location

6/23/97

Location

6/23/97

Location

6/23/97

Baker

1190

Fargo

1461

Linton

1291

Rolla

1003

Bismarck

1181

Forest River

1299

Mayville

1394

Streeter

1177

Bottineau

1112

Galesburg

1341

McHenry

1244

St. Thomas

1309

Cando

1223

Grand Forks

1351

Minot

1220

Towner

1090

Carrington

1211

Harvey

1160

Mohall

1093

Turtle Lake

1189

Cavalier

1233

Hillsboro

1381

Northwood

1269

Walhalla

1248

Columbus

981

Horace

1398

Oakes

1413

Williston

1235

Dazey

1303

Jamestown

1268

Prosper

1425

Wyndmere

1452

Edgeley

1292

Langdon

1087

Robinson

1205

   

* Adult female midge are present at 1300 DD
Sites in BOLD letters have or will exceed the degree days for female emergence shortly.


CEREAL APHIDS IN SMALL GRAINS

    The weather conditions have been favorable for establishment of cereal aphids in wheat fields. Bird Cherry-Oat aphid and English Grain Aphid are the primary aphids found.

    The critical time for making aphid treatment decisions is during stem elongation to heading. Treatment after heading has not been determined to be beneficial. Aphid impact on yield and quality is not great enough to justify the cost of control in headed wheat.

    What we have seen in the past is the Bird cherry-oat aphid tends to stay in the lower half of the plant, feeding on the leaves and lower stem. The English grain aphid is most often found on the developing wheat head. The growth rate, egg production, and rate of population increase is higher for English grain aphid when feeding on wheat heads than when they feed on leaves. This is why we tend to see this aphid's population build quickly once heading begins.

    The weather conditions have been favorable for aphid populations to increase. The more moderate temperatures favor aphids. However, the rains should provide some negative pressure on the populations. Frequently, aphids become infected with parasitic fungi. As the population builds and aphid densities increase, the infections occur and spread quickly. The decline in the population can be very dramatic. The infected aphids appear grey in color and fuzzy. It is not uncommon to see the populations collapse within a matter of days.

    Also, beneficial insects (lady beetles, lacewing larvae, syrphid fly larvae, parasitic wasps) increase quickly in our grain fields as the aphid numbers go up. This further puts pressure on the aphid population to start going down.

    Treatment guidelines for controlling aphids in wheat is when 85% of the stems have at least one aphid present from jointing to heading stages. Once heading is complete, treatment for aphids is not recommended.

 

ARMYWORMS POSSIBLE

    Armyworm infestations are possible under the current conditions. Moths have been captured in black light traps in the region. They lay their eggs in grasses, including small grains. They prefer moist, shady areas where grains or grasses have lodged. Over the next week scouting for armyworm larvae should intensify. Smaller larvae should easily be detected in wheat and barley with a sweep net. Check upper leaves for leaf notching. The recommended treatment threshold is 4 to 5 armyworm larvae per square foot. In corn, treat when 25 to 30% of the plants have 2 or more armyworms OR if 75% if the plants have 1 armyworm. If armyworms are migrating into fields, treat a couple of swaths ahead of the infestation to form a barrier strip.

 

ALFALFA WEEVIL CAUSING CONCERNS

    Alfalfa weevil larvae have been found at significant levels in alfalfa fields in the south central counties of North Dakota and neighboring areas of South Dakota over the past week. The 1/8 to 1/4 long larvae are pale green with a white stripe down the back. They can be found feeding on the leaves and leaf buds, most often in the top of the plant. They cause a ragged appearance to the leaves. Injury results in a whitish appearance to the field. The best management strategy would be to cut the alfalfa if it is near that time. Then watch for surviving larvae beneath the swath. If larvae survive, they will feed on the regrowth, but can be controlled with an insecticide easily after the hay is baled. Treatments in these cases can often be limited to the area where the swath was lying.


FIRST WAVE OF CORN BORER ACTIVITY

    Moth captures in the southeast quarter of the state were up during the past week and appear to be winding down for the moment These moths represent the earlier emerging, two generation type corn borer. The next flush of moth activity should be the single generation moths.

    It is time to start scouting for the presence of corn borer in fields. Look for the cluster of white eggs on the undersides of leaves, near the mid vein of the leaf. Look for small larvae in the whorl and shotholing in the leaves. The rain showers through the area should cause problems for these early larvae. Water collecting in the whorl of the plant promotes disease and drowning of young corn borer larvae.

Phillip Glogoza
Extension Entomologist


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