Insect Management

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 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.

The Dingy cutworm, Feltia jaculifera, overwinters as a partially grown larva and is one of the first cutworm species to cause problems during crop emergence from early to mid-May. Crops following sunflowers in rotation are at greatest risk of injury by this cutworm.

Other cutworms, the red-backed, Exoa ochregaster, and the darksided, Exoa messoria, overwinter as eggs which hatch in mid to late May. Eggs are laid in the fall and survive in weedy, wet, and reduced tillage areas. Feeding injury by these cutworms normally occurs in late May to early 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 (or diseases, in the case of the DM formulation) 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 2006 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 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. Field 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 2006 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 Soybean Cyst Nematodes
Soybean cyst nematode (SCN), a microscopic parasitic worm, was found in a number of fields in North Dakota (Richland County) for the first time in 2003. SCN is the most destructive pathogen of soybean worldwide. Once SCN 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 (~1 mm diameter); however, the use of a hand-lens will help in finding them.

The swollen female nematodes will be lemon-shaped and can be white, yellow, or brown in color; the nematodes are much smaller than the root nodules. Aboveground symptoms, although not always present, can appear as stunted and chlorotic plants. 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) to detect the presence of cysts or SCN eggs.

Once SCN is found in a field, yearly monitoring of the population is needed. To monitor the SCN population in a field collect soil samples in a zig-zag pattern throughout the field. Approximately 20 soil samples are needed for every 10 to 20 acres. Mix the samples together and send about 1 pt of soil to a lab. The best time to collect the samples is during the fall of the year. Dry edible beans are also a host of SCN, although more information on susceptibility and yield loss on dry bean is needed. A few resistant soybean varieties adapted to the southern valley are available, and more are in development.

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

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. – Montana State University Extension Service

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.

Stem Maggot May Cause White Heads in Wheat
White heads caused by wheat stem maggot feeding 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.

With wheat stem maggot damage, the head and the stem down to the top node are dead, with the rest of the plant green. The head will pull out with a gentle tug, and usually there is evidence of insect chewing on the stem above the top node where it broke when pulled. Single heads are affected rather than the whole plant. These symptoms can be differentiated from white heads caused by common root rot. 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. No chemical controls are available for wheat stem maggot.

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+

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 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. 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.

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.

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 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 not at economic damage levels. No RWA have been reported in North Dakota since the early 90s

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. Conclusions from 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.

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 binomial sequential sampling plan or “speed scouting” 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.

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 2006 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.

Cool Grain to Prevent Storage Problems

*Prevent crusting due to moisture migration by cooling grain to within 15^oF of average outdoor temperature. Cooling grain by 10^oF doubles its allowable storage time. 

(Source: Dr. Kenneth J. Hellevang, NDSU Extension Service).

Grain should be cooled to 20-25°F for winter storage. Aerate stored grain in the spring if needed, for storage into the summer. Aeration in the spring would be of particular concern for grain that went into storage last fall at moisture higher than recommended for long-term storage.

Online
Insect Info on the Internet

2006 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.ext.nodak.edu/extpubs/bugcrops.htm

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

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

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