Insect Management

Grasshoppers
In the Northern Plains, grasshopper egg hatch normally begins in late April to early May. The peak hatch occurs about mid-June and the hatch is usually nearing completion by late June. Cool and extremely dry springs may delay the hatch, allowing it to continue into July. Dry conditions increase the risk of grasshopper infestations. 

Whenever grasshopper populations reach the threatening level, feeding damage to crops should be anticipated. Directing control efforts at nymphs in hatching sites is recommended to minimize the total area requiring insecticide treatment, permits lower insecticide rates for effective control of small nymphs, and minimizes the potential for future crop damage.

More grasshopper management information can be found online at www.ndsu.nodak.edu/entomology. Click on the “Entomology Updates” link, then under field crop insects, click on “grasshoppers.” More grasshopper information and color survey maps can be found online at http://fs-sdy2.sidney.ars.usda.gov/grasshopper. Updated N.D. IPM grasshopper surveys can be found online during the growing season at www.ag.ndsu.nodak.edu/aginfo/ndipm.

Grasshopper Thresholds / Infestation Ratings

	Nymphs (Young hoppers) per square yard		Adults per square yard
Rating	Margin	Field	Margin	Field
Light	25 - 35	15-23	10 - 20	3 - 7
Threatening	50 - 75	30-45	21 - 40	8 - 14
Severe	100 - 150	60 - 90	41 - 80	15 - 28
Very Severe	200+	120	80+	28+

Orange Blossom Wheat Midge
Orange wheat blossom midge problems in Northern Plains wheat have been low the past few years. Weather conditions during the spring and summer are very important in determining if economic injury will occur.  If heading coincides with emergence of the midge and weather conditions are favorable for the female to lay eggs, producers will need to monitor fields, even in areas where the survey says populations are low, to determine if treatment is necessary. High soil moisture, warm and calm conditions, and high humidity favored midge egg laying in past years.

This year’s early planting should be beneficial in avoiding midge damage; with early planting, wheat can reach the flowering stage before significant levels of midge have emerged. Wheat is susceptible to midge infestation from the time the head emerges from the boot until 80% of the primary heads have anthers visible. More information online: www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/Wheat_Midge/owbm.htm .

Hessian Fly
The Hessian fly overwinters as a maggot or pupa in winter wheat, volunteer grain, and wheat stubble. Overwintered maggots pupate and emerge as adults from April to May, infesting winter and spring planted wheat. By June, maggots pupate (flaxseed stage), emerging as adults in August to lay eggs for the overwintering generation.  Thimet and Cruiser are registered as a planting time and a seed treatment for wheat, respectively, but populations of this pest rarely warrant the need for such treatments in North Dakota. Burying stubble and destroying volunteer grain after the first killing frost or early in the spring before fly emergence helps suppress adult populations.

Aphids
Greenbug, bird cherry oat, and English grain are common types of aphids in the Northern Plains. Treatment threshold is 85% stems with at least one aphid present, prior to complete heading. The greatest risk of yield loss from aphids feeding on grains is in the vegetative to boot stages.  Field scouting should begin at stem elongation and continue up to the heading stage of wheat. Aphid populations, at or above the thresholds, during these growth stages will result in economic injury to plants. The Russian Wheat Aphid can occasionally be found, but not at economic damage levels. No RWA have been reported in North Dakota since the early 90’s

Soybean aphid
Begin scouting fields at V3-V4.  No treatment recommended at this time and is discouraged, so insecticides do not reduce the presence of predators and parasites of aphids. The critical growth stage for making most soybean aphid treatment decisions appears to be the late vegetative to early reproductive stages (Vn-R3).  Assessing aphid populations at this time is critical.  Treatment to manage soybean aphid would be recommended at growth stages R1-R3, when aphids are abundant on most plants.  Treatment guideline: When aphids number 25 or more per sampled leaflet or 250 total aphids per plant.

Soybean Aphids (top) Soybean Aphid Infestation (bottom)

Corn borer
Managing corn borer is a challenge due to the lengthy emergence interval of the moths from overwintering. In N.D., borers have the potential for one or two generations during the season. The two generation borers are present in the southern region of the state. They begin emerging in early June and represent the first flush of larval feeding. The single generation borer is present throughout N.D., emerging from mid-June to August. The challenge is to distinguish when egg laying and larval populations can be tolerated or if they need to be controlled. Corn should be monitored weekly for at least five weeks once plants exceed an extended leaf height of 17 inches. At this point, corn borer larvae will be able to survive on the plant. Inspect plants for the presence of egg masses, whorl feeding, and active larvae. Observing moth activity around field margins or within the field may alert you to developing infestations. Recent corn borer infestations in N.D. developed in mid- to late-July and August as a result of the late emergence of the numerous single generation type borers.  In other years, the two generation borers emerging first may contribute more to significant infestations.  Field scouting worksheets and economic threshold guidelines can be found in the 2004 N.D. Field Crop Insect Management Guide, online at www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm   Scroll down and click on “Corn
Insects.”

– Phil Glogoza, NDSU
extension entomologist

Corn Borer larvae (top) Corn Borer Adult (bottom)

Herbicide, Insecticide Combinations
Though convenient for control of both weed and insect pests, some combinations have been shown to increase crop injury compared to either pesticide applied alone. Non-registered tank-mixtures should be used with caution until experience or research has shown that the combination is effective and safe. The following information is based on label restrictions and/or research indicating crop injury or decreased control.

2,4-D: Wheat injury but not lower wheat yield with 2,4-D amine combined with Lorsban. 2,4-D, bromoxynil+MCPA, Curtail mixed with Asana, Cygon, dicamba, Di-Syston, Warrior, or Lorsban caused no wheat injury in University of Wyoming studies.

Assert: Use caution when tank-mixing organophosphate insecticides for use on barley and sunflower. Assert and Di-Syston caused barley injury in University of Wyoming research.

Dicamba: Oil-based insecticides increase risk of wheat injury.

Basagran: Basagran should not be tank-mixed with Scout or any organophosphate insecticide as crop injury may result.

Betamix/Betanex: Increased sugarbeet injury occurred from tank-mixtures with Lorsban, malathion, or Sevin XLR. Oil-based additives increase risk of sugarbeet injury.

Bromoxynil: Refer to label for directions on the order of adding products to the spray tank and for the complete list of insecticides that can be tank-mixed with bromoxynil.

POST Grass Herbicide: Assure II, Fusilade DX, Fusion, Poast, Prism, Select:
Reduced grass control may result from tank-mixes of Fusilade DX with Lorsban, malathion, Sevin XLR, or Pydrin, or Poast mixed with Sevin XLR Plus or Pydrin. No decrease in grass control resulted from Poast tank-mixed with Lorsban or malathion.

Glyphosate: No antagonism or injury to resistant crops occurred when applied in combination with Warrior, Asana, Sevin, and Capture insecticides.

Stampede 80EDF + MCPA e + Oil additive: Do not tank-mix with any organophosphate or carbamate insecticide as serious crop injury will result. Apply malathion 14 days after application.

Sulfonylurea Herbicides (SU): Severe crop injury may result from tank-mixing SU herbicides with organophosphate insecticides. Most SU labels do not allow addition of Lorsban or malathion. SU herbicides and insecticides should be tank-mixed only when experience or research indicated crop safety.

 – NDSU Extension Service

Insect Info on the Internet

2004 N.D. Field Crop Insect Management Guide
www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

NDSU Crop Insect: www.ext.nodak.edu/extpubs/bugcrops.htm

North Dakota State University Entomology: www.ndsu.edu/entomology

SDSU Extension Entomology: http://plantsci.sdstate.edu/ent/

U of M Soybean Aphid Information Page:
www.soybeans.umn.edu/crop/insects/aphid/aphid.htm

Regional IPM Bugweb Insect Monitoring Network:
www.mnipm.umn.edu/BugWeb