Insect Management

Scouting for Armyworms in Wheat
Armyworm infestations occasionally develop following migrations of moths from southern states in late spring and early summer. Moths typically lay their tiny white eggs at the bases of plants in moist, shady areas, and prefer sites with lodged and/or hail-damaged grassy weed or crop plants. Eggs hatch and larvae quickly begin feeding on nearby plants. When armyworm larvae are young they will be pale green turning a dark green as they mature. Fully developed larva will grow to a length of 1 ½ to 2 inches. A series of stripes down the back and side of the body will be found.

Moth flights can occur over a few weeks time, so it is not unusual to find a wide size range of larvae present. Early detection of armyworm infestations is difficult because they feed at night and hide under vegetation or in loose soil during the day. Damage is sometimes obscured by wind injury or the dense small grain plant canopy itself. Armyworms are a favorite food of birds, so significant bird activity in a grain field can be an indicator of an armyworm infestation.

Scouting for armyworms in small grain fields involves parting the plant canopy back and searching for feeding injury or fecal pellets. If either is evident, look for larvae under plant trash, soil clods or in soil cracks. Fields can also be checked during evening hours (when larvae are most active) by shaking plants and using a flashlight to count dislodged larvae on the ground. Whether sampling during the day or in the evening, it is important to sample as many locations in a field as practical (at least 5 sites per field).

To avoid economic loss from armyworms, treat with a registered foliar insecticide when an infestation reaches 4 to 5 larvae per square foot. As the name implies, armyworms will assume the “army” habit and move in large numbers to neighboring fields when the food supply becomes depleted in the original feeding site. Applying a foliar insecticide as a barrier treatment to a strip of plant material ahead of the infestation in the direction of movement can provide good protection of neighboring fields if timed correctly.

Options for armyworm control in small grains can be found in the 2008 N.D. Field Crop Insect Management Recommendations guide online at: www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm. 

Online NDSU bulletin:
www.ext.nodak.edu/extpubs/plantsci/pests/e830w.htm.

Armyworms will also feed on other small grain crops as well as corn, alfalfa, clover, flax, and millet.

Scouting for Cutworms
Watch fields for any cut plants and dig up any cutworm larvae located under cut plants. Wet soil conditions will cause them to feed closer to the soil surface, and may make them easier to kill with insecticides.  Cool conditions can slow their feeding activities and larval development. Since there are early and later season cutworms, cutworm activity can continue into late June.

Early detection is critical for effective cutworm control, especially in corn, dry beans, sunflowers, soybeans, sugar beets, and alfalfa. Cutworm damage is often localized in certain areas of the field, and in some situations insecticide sprays can be targeted at those infested areas. Economic thresholds include:

Corn: Begin scouting for cutworms at stand establishment and continue until mid-June. Treat when 3 to 6% of the plants are cut and small larvae (<3/4 inch) are present. Application rate of 15 to 20 gallons of water per acre by ground application is suggested.

Dry Bean: Treatment is warranted when one cutworm or more is found per 3 feet of row and the larvae are small (<3/4 inch long).

Soybeans: Economic thresholds for cutworm treatment decisions are not well established. Treatment guidelines used over the years include when one cutworm or more is found per 3 feet of row and the larvae are small (<3/4 inch long). Another guideline is when 20% of plants are cut or when gaps of 1 foot or more exist in the plant row. When making a final decision, consider that surviving soybeans are able to compensate for early stand reductions because of the plants long growth period.

Sunflower: Treatment is warranted when one cutworm or more is found per square foot or there is a 25 to 30% stand reduction observed.

Keep in mind that while the seed treatment product Cruiser (a.i. thiamethoxam) has demonstrated success in controlling early-season insects such as wireworms, the product shouldn’t be expected to control insects beyond those listed on the product label.  Cutworms are not listed on the Cruiser label. Some have observed that Cruiser may help protect plants from cutworms early in the season. But the product shouldn’t be expected to offer complete control, especially as the growing season progresses, since it is not labeled for cutworms. 

A simple method of scouting cutworms to consider: Mix the labeled rate of an insecticide for cutworms in an ATV-mounted sprayer.  Three or four days after planting, make a diagonal spray pass across a sunflower field. Come back about an hour before sunset and again before sunrise to check dead cutworms in the treatment path. Scout early after the sample spray to get a good count.

Consult the 2008 ND Field Crop Insect Management Guide for insecticide registered for cutworm control in specific crops.
www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm.

Scouting Soybean Cyst Nematodes
Once Soybean cyst nematode (SCN), a microscopic parasitic worm, becomes established in a field , it is nearly impossible to eradicate. Therefore, keeping the SCN population levels to a minimum using crop rotation and resistant cultivars is the best way to manage this pathogen.

SCN survive as small cysts in the soil. The cyst is the actual body of a female nematode with hundreds of eggs inside her. When protected inside this cyst, the eggs are able to survive in the soil for multiple years. Swollen female nematodes on soybean roots are visible to the naked eye as a small lemon-shaped dot and can be white, yellow, or brown in color; the nematodes are much smaller than the root nodules.

Aboveground symptoms of SCN often include stunting, frequently expressed as a roller coaster effect. Infected plants may become yellow in July or August, and they have reduced vigor or mature earlier than those in surrounding areas of the field.

If SCN is suspected in a field, collect soil samples (6-8 in. deep) from the inside and margin of the affected areas, and send them to a lab (such as the NDSU Plant Diagnostic Lab or UM Nematology Lab in Waseca) to detect the presence of cysts or SCN eggs. A county extension educator or local agronomist can assist with identification and sampling.  Soil samples can be collected from early spring to late fall, but fall after harvest is an excellent time to collect samples for fields that will be planted into soybeans the following year.

U of M SCN bulletin online
www.extension.umn.edu/distribution/cropsystems/DC3935.html

SDSU SCN Factsheet:
http://agbiopubs.sdstate.edu/articles/FS902A.pdf

White females (small arrows) of SCN on soybean roots are visible to the naked eye, but are still very small, no bigger than the head of a pin. They shouldn’t be confused with nitrogen-fixing nodules on soybean roots (large arrow) which are much larger and are more pink/brown in color. Photo: North Central Soybean Research Program Plant Health Initiative

Stem Maggot May Cause White Heads in Wheat
White heads caused by feeding of wheat stem maggot larvae can often be observed in wheat fields. Typically, only 1 to 5% of the heads are affected, and they appear to occur scattered at random through the field. Normally the first indication of its presence is the dying and whitening of wheat heads and upper internodes while the lower stem and leaves remain green. A single maggot will be found inside the straw just above the last node. The plant stem pulls out very easily and if larvae are not found, the stem is usually cut off. The presence of white heads alone is not always an accurate assessment of damage. The maggots can also infest young tillers prior to the boot stage, causing the affected tiller to abort. These aborted tillers can account for an unseen loss in yield. Little is known about this insect pest, and no chemical controls are recommended.  Common root rot can also cause white heads, however with root rot, typically the whole plant is whitened and the whole plant easily pulls from the soil, with browned or blacked roots as well.

Orange Blossom Wheat Midge
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 have favored midge egg laying in past years.

Wheat is susceptible to midge infestation from the time the head emerges from the boot until 80% of the primary heads have anthers visible. Treatments are warranted when 1 or more midge are observed for every 4 or 5 heads of spring wheat, and when 1 or more midge are observed for every 7 or 8 heads of durum.  At these levels of infestation, wheat yields will be reduced by about 15% and lower the grade of harvested grains if the midge is not controlled. Treatments after 50% of the first heads have flowered are not recommended, due to reduced levels of efficacy and for the protection of a parasitic wasp that attacks the midge eggs.

Not every small fly in the crop will be a wheat midge. Wheat midge is a small, fragile, orange fly about 2 to 3 millimeters in size. Another small fly that is common in wheat fields is the lauxanid, which is larger (2.5 to 4 mm), more robust and yellowish brown. The wheat midge tends to flutter from plant to plant and rests with its head pointing skyward. The lauxanid flies and rests in a horizontal position with its head pointing toward the ground.

Scout fields after 9 p.m. if the temperature is above 59 degrees and the wind speed is less than 6 mph. Count the number of adult wheat midge present on four or five heads at several locations and then use an average per field.

A newer alternative to field scouting is using sex pheromone traps or yellow sticky traps to monitor for wheat midge in wheat fields. Traps are placed next to the wheat head at the beginning of heading and collected in three to five days. Three sex pheromone traps ($7.20 a trap) per 160-acre wheat field or 10 yellow sticky traps (60 cents per trap) per field are recommended. The number of wheat midge per trap is counted and the average per trap calculated.

Action thresholds are nine wheat midges per sex pheromone trap and five to 20 wheat midges per yellow sticky trap. Sex pheromone traps are available through PheroTech International (http://pherotech.com). Yellow sticky traps are available through Great Lakes IPM (http://greatlakesipm.com) or PheroTech International. Specific trapping guidelines also are available through distributors.

The wheat midge degree-day model developed in Canada has helped predict emergence and peak activity periods, as well as when field monitoring should take place. Using a base of 40 degrees Fahrenheit, 90% of female wheat midge has emerged by 1,600 degree days. Actual degree days are calculated and maps available for producers on the NDSU NDAWN Web site at
http://ndawn.ndsu.nodak.edu/wheat-midgegdd-form.html.

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, 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.

Soybean aphid
Begin scouting fields at V3-V4. However, no treatment recommended at this time and is discouraged, so insecticides do not reduce the presence of predators and parasites of soybean aphids, such as the Multicolored Asian lady beetle. 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. Research has found that the best results from an aphid treatment occurred from mid-July to early August. Treatment to manage soybean aphid would be recommended at growth stages R1-R4, when aphids are abundant on most plants. Treatment guideline: When aphids number 25 or more per sampled leaflet or 250 total aphids per plant.

More than 100 soybean aphids on the underside of a soybean leaf. Pest feeding can inhibit the plant’s ability to make grain, or kill it outright. (Photo John Obermeyer, Purdue Extension entomologist)

The recommended economic threshold for R5 (seed fill) growth stage is increasing aphid populations and above 250 aphids per plants on 80% of the plants in field. This would require multiple scouting trips to determine a growing aphid populations and not static one. Research indicates little yield benefit to treating soybean aphid populations at the R6 (full seed) growth stage. Common sense should be used in determining treatments for soybean aphid in R5/R6 soybean including yield expectations, net returns, moisture stress, and increasing or decreasing aphid populations.

With high temperatures (>90 F) the upper limit of any foliar insecticide is about 2 weeks, with one week to 10 days more realistic.  On the positive side, high temperature above 90 F will also slow and eventually stop reproduction of soybean aphids and increase mortality rates (shorter life span of only 11 days compared to a typical 30-39 day life span).

Synthetic pyrethroid insecticides (e.g. Warrior, Asana XL, Decis 1.5 EC, Proaxis, Taiga Z) have been shown to generally provide longer suppression of aphid populations than most organophosphate insecticides (OPs, e.g. Lorsban 4E, Penncap-M, Orthene). However, the OPs have been observed to work more quickly, and are not affected by high temperatures of >90F like SPs are. Keep preharvest interval in mind, which can range as little as 14 days for Orthene 97 Pellets and Lannate LV to as much as 60 days for Pounce 3.2 EC and Arctic 3.2.

Soybean aphids have tended to initially colonize fields near shelterbelts, southern field edges, or perhaps some other protective structure. Particular attention should be given to smaller fields (less than 30 acres) that are surrounded by wooded areas. Check field edges first to detect the earliest colonization.  Surveys have indicated that it takes about 3 to 4 weeks for aphids to be detected in other areas of the field. Eventually, the larger colonies develop where initial colonization occurs.

Another method of sampling developed at the University of Minnesota is a “speed scouting” sampling method recommended for use through the pod fill stage.  If a plant has less than 40 aphids, consider it non-infested; however if the plant has 40 or more aphids (counting additional aphids is not necessary after 40), consider the plant infested. Based on the speed scouting sampling plan, three treatment decisions are possible: 1. Do not treat the field; 2. Treat the field; or 3. Resample the field in 3-4 days. More information about the speed sampling method on the Internet:
 www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm.

An NDSU Bulletin on managing soybean aphids can be found online at www.ext.nodak .edu/extpubs/plantsci/rowcrops/e1232w.htm.

Aphids in Small Grains 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, or 12-15 aphids per stem, prior to complete heading. The greatest risk of yield loss from aphids feeding on wheat 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 generally not at economic damage levels.

European 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.

Corn borer larvae Corn Borer Adult Moth

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.

Degree day models have been used to predict the flight occurrence of corn borer moths, and can help identify priority times for field scouting. Degree day information for corn borer can be found online at www.soils.wisc.edu/wimnext/corn/euroborer.html and http://ndawn.ndsu.nodak.edu/index .html.

Field scouting worksheets and economic threshold guidelines can be found in the 2007 N.D. Field Crop Insect Management Guide, online at www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm.  Scroll down and click on “Corn Insects.”

Worksheets and more information for treatment decisions can also be found online at http://nwroc.umn.edu – on the home page, click on ‘Cropping Issues of NW Minnesota.’ In the menu at left, under ‘Cropping Issues Newsletter’ select ‘past issues’ and under 2006, go to Issue 8, 7-11.

Managing Grasshoppers
Peak hatch in the Northern Plains usually occurs about mid-June, and usually nears 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, and permits lower insecticide rates for effective control.

Grasshopper management 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+

Herbicide-Insecticide Combinations
Combinations are convenient for control of both weed and insect pests. However, some combinations have been shown to increase crop injury compared to either pesticide applied alone. Efficacy data on herbicide-insecticide mixtures are limited because of the number of potential combinations. 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, dicamba, bromoxynil+MCPA or Curtail mixed with Asana, Cygon, 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.

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.

Compatibility Test for Pesticide Mixture
Under federal law, combining pesticides is legal unless the pesticide labeling of any of the pesticides involved instructs you not to combine them. However, not all pesticides work well when mixed together. They must be compatible — that is, mixing them together must not reduce their safety or effectiveness. The more pesticides you mix together, the greater the chance of undesirable effects. 

A way to test for tank-mix compatability:
Get a large, clean, clear glass container, such as a quart jar. Use the same water (or other diluent) that you will use when making up the larger mixture. Add the water and each of the products in the same proportions as you will mix them. For example, each quart of pesticide that you add to 50 gallons of final spray mixture is the equivalent of about 1 teaspoon per quart of water. Unless the pesticide labeling states otherwise, add pesticides to the diluent using the “W-A-L-E” plan:

• Add some of the diluent first
• Add Wettable and other powders and water-dispersible granules
• Agitate thoroughly and add the remaining diluent
• Add the Liquid products, such as solutions, surfactants, and flowables
• Add Emulsifiable concentrates last

Shake the jar vigorously. Feel the sides of the jar to determine if the mixture is giving off heat. If so, the mixture may be undergoing a chemical reaction and the pesticides should not be combined. Let the mixture stand for about 15 minutes and feel again for unusual heat.

If scum forms on the surface, if the mixture clumps, or if any solids settle to the bottom (except for wettable powders), the mixture probably is not compatible. Finally, if no signs of incompatibility appear, test the mixture on a small area of the surface where it is to be applied.

Resolving Incompatibility
Add 6 drops of compatibility agent and stir well. If mixture appears compatible, allow it to stand for 1 hour, stir well, and check it again. If the mixture appears incompatible, repeat one or two more times, using 6 drops of compatibility agent each time.

If incompatibility still persists, dispose of this mixture, clean the jar, and repeat the above steps, but add 6 drops of compatibility agent to the water before anything else is added.

If the mixture is still incompatible, do not mix the chemicals in the spray tank.

To overcome this problem you might consider the following alternatives:

a) Use a different water supply. Hard water can contribute to incompatibility.

b) Change brands or formulations of chemicals.

c) Change the order of mixing.

Make only one change at a time, and perform a complete test, as described above, before making another change. Do not mix the chemicals in the spray tank if incompatibility cannot be resolved.

The Effect of Water pH on Insecticides
Alkaline water (containing soluble mineral salts – alkaline waters are considered to be hard water) used in spray mixtures can seriously reduce the effectiveness of some insecticides, particularly if the mixture is left standing in the spray tank for an extended period of time. Insecticides classified as organophosphates and carbamates break down easily in high pH water. Use water of pH 7.00 or less with these insecticides. The pH of any solution will be between zero and 14, with anything below seven being alkaline. To compare, lemon juice is acidic with a pH of two. Milk of Magnesia is alkaline with a pH of 10.5, and distilled water is neutral with a pH of seven. If water having a pH of 7.0 or less is not available, use a buffering agent to alter the water pH. Buffering agents can be purchased from agricultural chemical dealers. Water pH testing kits can be bought from some ag dealers.

Insect Info on the Internet

2008 N.D. Field Crop Insect Management Guide: 
www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

Insect Updates for N.D.:
www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/index.htm

NDSU Crop Insect Publications:
www.ag.ndsu.edu/pubs/bugcrops.html

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

NWROC Crookston Entomology:
http://nwes.umn.edu/html/entomology.htm

* Prevent crusting due to moisture migration by cooling grain to within 15^o F of average outdoor temperature. Cooling grain by 10^o F doubles its allowable storage time. (Source: Dr. Kenneth J. Hellevang, NDSU Extension Service)

Grain should be cooled to 20-25°F for winter storage. If desired, the grain can be warmed to 35 -40°F in March for storage into the summer. The goal should be to keep the grain cool to enhance its storability. Keeping the grain cool will reduce the potential for insect infestation and grain spoilage.

Common Conversions Bushels to Metric Tons bu. x 0.027216 = MT wheat or soybeans bu. x 0.025400 = MT corn bu. x 0.021772 = MT barley Bushels/Acre to Metric Tons/Hectars: bu./acre x .06725  = MT/ha. wheat or soybeans bu./acre x .06277  = MT/ha. corn bu./acre x .05380  = MT/ha. barley Pounds/Bushel to Kilogram/Hectoliter: lbs./bu. x 1.287 = kg./hl. Metric Tons to Bushels: MT x 36.74 =  bu. wheat or soybeans MT x 39.36 =  bu. corn MT x 45.92 =  bu. of barley Metric Ton/Hectare to Bushels/Acre: MT/ha. x 14.87 = bu/acrekg./hl. x 0.777 = lbs./bu. Other: 3 teaspoons=1 tablespoon=14.8 ml 2 tablespoons=1 fluid ounce=29.6 ml 1 mph=1.609 km/hr. 1 mph=68 seconds/100 ft. 1 mph=88 ft. min. 1 lb/acre=1.1209 kg/ha 1 gallon/acre=9.3541 liter/ha 1 qt/acre=2.3386 l/ha 1 horsepower=0.746 kw 1 liquid pint = 16 fl oz = 0.473 liter 1 liquid quart = 2 pints = 0.946 liter 1 liquid gallon = 4 quarts = 3.785 liters 1 acre = 43,560 square feet