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ISSUE 6  June 11, 1998

 

ORANGE WHEAT BLOSSOM MIDGE UPDATE

    Adult midge emergence begins around 1100 to 1200 degree days (DD) at a base temperature of 40 F. The males are the first to emerge, though. Female emergence begins when 1300 DD. In southeast and eastern North Dakota, we are quickly approaching the time when wheat midge will begin emerging. Because of the early warm temperatures emergence is going to occur earlier by about ten days when compared to our experiences the past two years.

    In order for the midge to cause economic damage, they must be present at a population level of 1 adult midge per 4 to 5 wheat heads, the wheat must have primary and 1st tillers with heads emerging but prior to 80% flowering. Weather conditions during egg laying must be favorable for midge (warm, humid, and with very little wind).

 

Wheat Midge DD Accumulations (Base 40 F)*

Location

6/08/97

Location

6/08/97

Location

6/08/97

Location

6/08/97

Baker

879

Fargo

1073

Linton

949

Rolla

706

Bismarck

849

Forest River

958

Mayville

1029

Streeter

851

Bottineau

792

Galesburg

988

McHenry

917

St. Thomas

954

Cando

896

Grand Forks

998

Minot

896

Towner

768

Carrington

884

Harvey

828

Mohall

784

Turtle Lake

866

Cavalier

886

Hillsboro

1013

Northwood

945

Walhalla

896

Columbus

704

Horace

1022

Oakes

1032

Williston

921

Dazey

959

Jamestown

929

Prosper

1049

Wyndmere

1060

Edgeley

947

Langdon

778

Robinson

865

   

            *Adult female midge are present at 1300 DD

 

ORANGE WHEAT BLOSSOM MIDGE -THE BASICS

Biology

    Adult wheat midge are small, orange flies, about half the size of a mosquito. They have overwintered in the soil of infested wheat fields from last year. The adults emerge from the soil beginning in late June and early July. Peak activity, and the greatest risk of infestation, is expected during early to mid July.

    Egg laying takes place after 8:30 p.m. when the air temperature is greater than 60 F and the wind speed is less than 6 mph. Eggs are laid on wheat heads around and on the florets. Eggs hatch in 4 to 7 days.

    Larvae are orange colored. They feed on the developing kernels within the glume. No changes in external appearance of the wheat plant takes place. Larvae feed for about 2 to 3 weeks and grow to 1/8 to 1/4 inch long. They drop from the wheat heads in August after rain or heavy dew.

Wheat is the most important host plant. Barley is not very susceptible to wheat midge.

Action Threshold

- Deciding to treat

    Wheat is ONLY susceptible to midge attack between heading and flowering.

    The decision to treat wheat for midge should be determined by growth stage and the number of midge found on wheat heads during the evening scouting activities.

    The action threshold is 1 adult midge per 4 to 5 wheat heads inspected (primary heads and first tillers). At this level of infestation, yield reductions are estimated to be 15%.

How to Scout for Wheat Midge

    Monitor wheat fields between heading and flowering. Field scouting must be in the evening from 9:00 pm until midnight. Wind speeds should be below 6 mph and temperatures above 59 F. Wheat midge ADULTS can be seen laying eggs on the wheat heads.

    Monitor from HEAD EMERGENCE until 80% of the heads have ANTHERS VISIBLE. When anthers are visible, a wheat head is flowering.

    Visit 3 or 4 different sites in the field. At each location, count the number of midge on several sets of wheat heads (4 to 5 heads per set). Record and calculate your average for the field.

Detecting Wheat Midge

- Other Methods

    Scouting is the only recognized way of arriving at an accurate decision to treat a field. There are other methods that may be used to detect the presence of midge in a field for the purpose of recognizing adult wheat midge. None of these methods are reliable for making treatment decisions.

emergence traps - a container placed on the soil surface to collect midge as they emerge from the soil. Aids in recognition of midge and alerting a person to the start of emergence.

sticky traps - white traps, coated with oil, placed at the same height as the wheat plants and lower in the canopy. Midge adults become stuck to the traps. Aids in recognition of midge and alerting a person to the presence of midge.

pie tins, paper plates, etc. - these have been used to quickly collect adult midge in fields for aid in recognition of the insect. Apply cooking oil to the surface of the object and sweep it through the canopy of the wheat plants. Midge and other insects should stick to the surface for easier identification.

Insecticides for Wheat Midge

    The only registered product in North Dakota with wheat midge on the label is Lorsban 4E-SG at a rate of 1 pint per acre. Ground or aerial application can provide effective control when timed properly.

Aerial - apply in a minimum of 2 gallons of water per acre. Applications should be made in the late afternoon or early evening for best results.

Ground - apply in a minimum of 10 gallons of water per acre, using 40 to 45 PSI. Angle nozzles forward at a 45 degree angle. Applications throughout the evening should be effective.

Tank mixing - Lorsban 4E-SG can be mixed with most fungicides. Avoid tin, copper, and zinc materials when mixed for greater than 12 hours. Do Not Apply with Supertin.

Timing Treatments

Timing a treatment is critical for getting the best results. Apply insecticides before 9 a.m. in the morning, or after 6:30 p.m. in the evening, and when the crop is heading to flowering.

If the action threshold is reached, then consider the following:

 

CUTWORMS CONTINUE TO CAUSE DAMAGE AROUND THE STATE

    Numerous problems with cutworms have been reported from around the state. The most recent concerns are in the central counties of Eddy, Foster, and Griggs, but are not restricted to these areas. Crops most severely impacted have been our most recently planted crops, including sunflowers, soybeans, and dry beans. In many cases, the cutworms are reported to be feeding on the seedlings before or as they emerge. The below ground feeding poses a serious problem and one that has no good solution. When cutworms feed above ground, the post emerge insecticides are effective. When the cutworms are feeding below ground, even treating with an insecticide such as Lorsban and hoping for movement down into the soil is not likely to provide control.

    In these cases where feeding is on seedlings prior to their emergence, the best advice may be patience. The cutworms begin to pupate when they reach a size of 1 to 1 inches in length. At that time, evaluate the condition of the remaining stand and consider the need for replant.

 

SEEDCORN MAGGOT AFFECTING DRY BEAN EMERGENCE

    There have been numerous reports of emergence problems with dry beans and, in some cases, soybeans and sunflowers that can not be blamed on cutworms. What we are finding is damage from seedcorn maggots feeding on the emerging seedling. The small white maggots have been feeding below ground, between the cotyledon leaves of these crops. The result is badly damaged leaves that often break from the emerging stem, leaving a cotyledon-less plant. The growing point is often damaged, a condition known as "snakehead." Seedlings often die; those that survive are often weakened. There are multiple generations of seedcorn maggot during the season. If replant is required, the use of an insecticide seed treatment is recommended. Seedcorn maggots are most often a problem when wet, cool conditions are present, organic matter such as crop residue or manure is present, and seedlings are slow to emerge. The recent cool weather occurred when many acres of dry beans had ben seeded. There slow emergence resulted in the maggots getting the upper hand.

Phillip Glogoza
Extension Entomologist


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