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ISSUE 7   June 24, 2010

2010 WHEAT MIDGE FORECAST & SCOUTING GUIDELINES

Soil samples in North Dakota indicate increasing levels of overwintering wheat midge larvae for the 2010 season (Fig. 1). County extension agents and area specialist collected a total of 186 soil samples from 20 counties in the fall of 2009 to estimate the regional risk for wheat midge. The distribution of wheat midge in the 2010 forecast map is based on unparasitized cocoons found in the soil samples collected.


Figure 1.
2009 Wheat Midge Larval Survey ND

The 2010 forecast for wheat midge risk has increased from 2009, especially in Divide, Burke, Renville, Mountrail and Towner counties. Wheat midge populations ranged from zero to 750 midge larvae per square meter, with an average of 129 larvae per square meter among the positive samples in 2009. In contrast, wheat midge populations ranged from zero to 286 midge larvae per square meter, with an average of 70 larvae per square meter among the positive samples during 2008.

Areas where populations are above 500 larvae per square meter can cause economic damage if the wheat crop is heading during adult wheat midge emergence, so wheat producers will need to be alert to wheat midge emergence and population levels. A pocket of 501 to 800 midge larvae per square meter was found in northeastern Divide. There also are several pockets of 201 to 500 larvae per square meter in the eastern half of Divide County, northwestern Williams into southwestern Divide, north-central Burke, central Renville and two small pockets in north and south Towner County.

Areas with more than 200 midge larvae per square meter should be scouted to determine if an action threshold population level exists. However, these areas are not considered high risk (more than 1,200 midge larvae per square meter). There were no soil samples that were considered a high risk for wheat midge infestation. At high risk, some control tactic, such as insecticide spraying or planting a nonwheat host, is recommended to mitigate midge populations.

With a low to moderate forecast for wheat midge infestation statewide, field scouting will be critical to indicate where economic population densities occur during the growing season.

Scouting should be conducted at night when temperatures are greater than 59 degrees and the winds are calm (less than 6 miles per hour) during heading to early flowering crop stages. The adult wheat midge (Fig. 2) is an orange color, fragile, very small insect approximately half the size of a mosquito. It is about 0.08-0.12 inch (2-3 mm) long with three pairs of long legs.


Figure 2.
Wheat midge adult (NDSU Ext. Ent.)

Be careful not to confuse the Lauxanid fly, Camptoprosopella borealis (Diptera: Lauxaniidae) with wheat midge. The Lauxanid fly is yellowish-brown in color and larger than the midge about 1/10 to 1/6 inches (2-4 mm) in length (Fig. 3). It also actively flies above the wheat canopy during the day and early evening. In contrast, the wheat midge flutters from plant to plant only in the evening. At night, the Lauxanid can be observed resting in the wheat canopy in a horizontal position with its head pointing down in contrast to the wheat midge, which rests with its head pointing upwards.


Figure 3.
Lauxanid fly (left) and wheat midge (right)
(Saskatoon Research Centre, Canada).

To aid scouting, a degree day (DD) model has been developed to predict the emergence of adult midges. The threshold temperature for wheat midge development is 40 degrees F. Observations indicate the following DD accumulations for wheat midge development:

450 DD - Wheat midge breaks larval cocoons and moves close to the soil surface to form pupal cocoons
1,300 DD - 10 percent of the females will have emerged
1,475 DD - About 50 percent of the females will have emerged
1,600 DD - About 90 percent of the females will have emerged

The current DD map (Fig. 4) for wheat midge emergence indicates that the southeast region is close to 90% emergence, emergence is just starting in the northeast and parts of north central regions and no emergence in the northwest region. Since the wet weather has been ideal for wheat midge emergence, there is some concern that any heading wheat in the Red River Valley (RRV) may be at risk for wheat midge this year. The soil survey does not include the RRV that has had low populations over the past decade. Again, scouting can help determine if these fields will be at any risk for wheat midge in 2010.


Figure 4.
Wheat midge degree day map (NDAWN)

The DD model can be found on the North Dakota Agricultural Weather Network (NDAWN) at:

http://ndawn.ndsu.nodak.edu/wheat-midgedd-form.html.

When wheat midge is emerging, wheat is susceptible in the heading to early flowering growth stages. An insecticide should be applied during heading and when the adult midge density reaches one midge per four to five wheat heads for hard red spring wheat or one midge per seven to eight heads for durum. A late insecticide application should be avoided to minimize negative impacts on the parasitoid. Wheat midge larvae feed on the kernel and negatively affect yield, grade and quality.

The parasitic wasp, Macroglenes penetrans, (Fig. 5) also helps reduce wheat midge populations.


Figure 5.
Parasitoid of wheat midge (Saskatoon Research Centre, Canada).

There was a slight increase in the average parasitism rate from 9 percent in 2008 to 13 percent in 2009 (Fig. 6). Overall, parasitism ranged from 0 percent to 100 percent across the state, with the higher rates occurring in areas where midge populations have been high the past few years.


Figure 6.
Percent Parasitism from 2009 Wheat Midge Larval Survey ND

An NDSU Extension Service publication, IPM of the Wheat Midge in North Dakota (E-1130), is available at:

http://www.ag.ndsu.edu/pubs/plantsci/pests/e1330.pdf.

The wheat midge survey is supported by the North Dakota Wheat Commission.

 

SCOUT FOR ARMYWORMS IN WHEAT

There has been a few reports of true armyworm (Pseudaletia unipuncta) feeding in wheat in the northeast region near Grand Forks and south central region near Wishek. There has been a lot of southerly wind flows, which can blow large numbers of armyworm moths into North Dakota from the southern states. Moths prefer to lay eggs in moist, shady areas and in small grains or grasses that have lodged or been damaged by hail or wind. Armyworms feed at night and hide under vegetation or in loose soil during the day.

The adult moth has a wingspan of about 1½ inch long (Fig. 7). Forewings are brown with dull luster, and a white spot near the center.


Figure 7.
True Armyworm adult moth (G. Fauske, NDSU)

Larvae are about 1¼ inches long when mature and prefer cool, wet weather. Larvae vary in color from green to brown with a dark stripe pattern running down the length of the abdomen on each side of the insect (Fig. 8). There are three pairs of true legs near the head and five pairs of fleshy prolegs with a black band on the prolegs.


Figure 8.
True Armyworm larva (B. Potter, UMN)

Larvae defoliate host plants. Young leaves will be completely eaten, and older leaves may be skeletonized leaving only the leaf veins uneaten. Often damage in a field may be spotty with field margins being the most prone to armyworm damage. In wheat, heads can be clipped. Outbreaks tend to occur following cool wet springs.

To scout for armyworm larvae in grains, part the plants and inspect the soil for fecal pellets. If pellets or feeding damage is found, look for larvae under plant trash, soil clods or in soil cracks.

The action threshold for armyworms in wheat is:

Treat when 4 to 5 or more worms per square foot are present.

For insecticides registered in North Dakota for cutworm control, consult the 2010 Field Crop Insect Management Guide at:

http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm

 

ADULT SUNFLOWER BEETLE EMERGING

Adult sunflower beetles (Fig. 9) are emerging in the north central region of North Dakota (see Waldstein’s report in ‘Around the State’). Populations of sunflower beetles have declined in recent years compared to the mid-late 1990s. The wide scale use of insecticide seed treatments in sunflower is effective in controlling adult sunflower beetles and could be part of the reason.


Figure 9.
Sunflower beetle adult (P. Beauzay, NDSU)

Damage is caused by defoliation from the adult and larva of sunflower beetle. Adults feed in the day and feeding is concentrated on the true leaves. Adults quickly begin laying pale yellow eggs singly on stems and the underside of leaves. Eggs hatch in about 8 days. The pale green, humpbacked larvae (Fig. 10) begin feeding, eating holes throughout the leaf. Larvae do not feed during the day, resting in the plant tops where they are easily observed.


Figure 10.
Sunflower beetle larva (NDSU Ext. Ent.)

The Economic or Action Threshold for sunflower beetle is:

Adults - Treatment is recommended when scouting determines that an average of 1 to 2 beetles per plant can be found throughout the field.

Larvae - When an average of 10 to 15 larvae per plant is found, defoliation levels of 25% to 30% would be expected. Treatment is suggested when damage levels reach this point and most larvae are 1/4 inch in size.

Please see the NDSU Extension Service Factsheet on sunflower beetle for more information:

http://www.ag.ndsu.edu/pubs/plantsci/pests/e824.htm

 

UPDATE ON DEGREE DAYS FOR COLLECTING LEAFY SPURGE FLEA BEETLES

The accumulated growing degree days (AGDD) for sunflower (base of 44 F) can be used as a guide to determine when to begin scouting for adult flea beetles. Begin scouting for adult flea beetles when the AGDD approaches 1,000. Flea beetles should be collected between 1,200 and the 1,600 using the sunflower GDD from NDAWN. Only the southeastern region of North Dakota has accumulated over 1,200 growing degree days (GDD, Fig. 11).


Figure 11.
Leafy spurge flea beetle degree day map (NDAWN)

 

FUN INSECT QUESTION: WHAT IS THIS LARGE SPIDER? IS IT POISONOUS?


Figure 12.
Mystery spider (P. Beauzay, NDSU)

This is a female fishing spider, raft spider, dock spider or wharf spider in the genus Dolomedes and Family Pisauridae. Nine species of Dolomedes exist in North America. Almost all Dolomedes spiders are semi-aquatic and have a striking pale stripe down each side of the body. In spite of their large size (leg span of up to 3 inches), they are not poisonous. They hunt in the night by waiting at the edge of pools or streams and preying on mayflies, aquatic insects and small fish. To capture their prey, the spider extends their legs on the water surface to detect vibrations given off by prey. These spiders also are capable of climbing beneath the water to capture prey and escape predators (birds).

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

SUGARBEET ROOT MAGGOT: FLY ACTIVITY HOTSPOTS PERSIST

Most of the sugarbeet root maggot fly activity for this growing season has taken place by now. However, the rare periods of warm, rain-free, calm weather that occurred in a few spots in the Red River Valley during the past few days have allowed later-emerging flies to take flight and search for beet fields in which to mate and/or lay eggs.

As of June 21, the NDSU root maggot trapping network detected moderate levels of continued activity in the Auburn and St. Thomas areas of the Valley. This persistent fly activity is a result of the fact that there have been very few periods of optimal weather for flight activity since the area reached the necessary accumulation of degree-day units for peaks to occur.

No major resurgence in root maggot fly activity is expected for the rest of the growing season, but fields in central and southern Pembina county should continue to be monitored. If fly activity in a particular field exceeds about 1 fly per 2 plants, the field should be checked daily to determine if activity increases. Fields lacking a previous postemergence insecticide application should be treated if activity reaches about 0.75 flies per plant on average across the field. To view NDSU's sugarbeet root maggot trapping network results, visit

www.ndsu.edu/entomology/people/faculty/boetel/flycounts/

These counts are only indicators of actual fly activity in the specific fields in which they were collected. They are not intended to be a replacement for growers’ monitoring activity in their own fields.

 

CUTWORMS DAMAGING SUGARBEET FIELDS

Several instances of cutworm damage and continued feeding activity in Red River Valley sugarbeet fields have been reported in the past two weeks. Fields should be monitored closely during the next couple of weeks to determine if insecticide treatment is warranted.

Cutworms typically feed overnight and rest below the soil surface during daytime hours. However, if the upper zone of soil is extremely wet or completely saturated, they may be found on plants. Damage typically occurs as completely cut plants at the soil surface or petiole damage that can continue right down to the plant crown. However, during periods of wet soils, feeding will be more prevalent on foliage.

The published economic threshold for cutworm infestations in sugarbeet is if 4 to 5% cutting of seedlings is observed. However, insecticide treatment may not be justified in fields with high plant populations (190-220 plants/100 ft). Control may be justified for fields with more mature (10-leaf or larger) plants if infestations of 3 to 5 larvae per square foot are detected.

It is desirable to apply insecticides during late afternoon or evening hours. This can maximize the amount of insecticide material present during the first nighttime hours following application when larvae are most active. Liquid insecticide formulations generally provide better and quicker control of cutworms, especially during very periods of dry weather. Avoid applying a foliar liquid insecticide during afternoons when the high temperature exceeds 85 F. Granular insecticides containing chlorpyrifos as the active ingredient (Lorsban 15G, Nufos 15G, etc.) will work well in moist soil conditions. If the soil surface of a field slated for a granular insecticide application is crusted, the crust should be broken up before or during the insecticide application.

Mark Boetel
Research & Extension Entomologist
mark.boetel@ndsu.edu


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