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ISSUE 2   May  17, 2007


Crucifer flea beetles have been observed feeding on volunteer canola. Adult flea beetles overwinter in the shelterbelts and leaf litter near last year’s canola fields. The tiny, black colored flea beetles with a metallic bluish sheen move into the canola fields just as the seedlings are emerging (see photograph). Adults feed on the cotyledons and first true leaves of seedlings causing pitting and holes in the leaves (see photograph). Damage is most serious to seedling plants and can cause seedling death and significant stand loss. Monitor newly emerged canola for high densities of adult flea beetles and assurances that seed treatments are properly working. Hot, sunny weather increases feeding activity and movement; while cool, damp weather slows feeding and favors crop growth. If the seed treatment did not provide adequate protection or was not used, an application of a foliar insecticide may be necessary. Foliar applications are recommended when 25% DEFOLIATION OCCURS ON THE COTYLEDONS AND TRUE LEAVES (Economic Threshold Level). Please consult 2007 North Dakota Insect Management Guide for listing of insecticides registered in ND.

Flea beetle            Pitted seedling
Flea beetle (G. Fauske)                            Pitted seedling (J. Knodel)



As of May 13th, the "Crop, Livestock and Weather" Report from NASS-UDSA reported that favorable weather allowed producers to advance small grain planting progress ahead of average in North Dakota. Spring wheat seeded, at 85 percent, advanced 25 percentage points from the previous week, over a week ahead of the average pace. This is good news for HRSW producers who planted early. Early-planted HRSW that was seeded before May 9th will head prior to the emergence of wheat midge minimizing potential economic injury (see map). The following Degree Day table describes the intervals of when wheat is at risk to wheat midge.

HRSW planted PRIOR to accumulating 200 DD will head before significant numbers of wheat midge emerge.

HRSW planted FROM 200 to 600 DD will be heading at the time wheat midge are emerging and is at greatest risk to infestation.

HRSW planted AFTER 600 DD will head after peak emergence of midge and should be at lower risk to midge infestation (late planted wheat is at greater risk to cereal aphid infestations, barley yellow dwarf viral infections and exposure to frost injury).

Wheat growing degree day map

We must remember that temperature drives midge development as well. However, for economic damage from wheat midge to occur, the right weather conditions must exist besides wheat being in the susceptible stage, heading to early flowering. For example, wheat midge must have adequate soil moisture for adult emergence from the soil. For egg laying, midge also requires warm temperatures, calm conditions, and moisture during heading. Soil conditions in reduced tillage situations will vary from normal tillage conditions and may delay some midge emergence in a region. Conditions that favor survival of adult midge may put even later planted wheat at some risk. Scouting for adult midge activity is the best way to avoid unnecessary losses due to wheat midge infestations.

Although DD are useful in predicting development of crops and many insect species, these predictions are only estimates. The accuracy of a DD estimate is dependent on the temperatures used in calculating degree days. DD should be calculated with temperatures that represent the environment where crops/insects are developing. Temperatures at one site give only a rough estimate of crop/ insect development at another site miles away.



Reports from Illinois indicate that they found lower numbers of winged soybean aphids in buckthorn (overwintering host) than expected based on 2006 fall survey, which found large numbers of overwintering eggs. Illinois entomologists believe that the cold weather in early April may have directly killed aphids that hatched from eggs in late March or that the buckthorn foliage was killed by the hard freeze, leaving the aphid without any nutritional sources. Although aphid populations are lower than expected, aphid colonies were still abundant on buckthorn in Illinois. However, with the delayed planting of soybean and emergence still several weeks away, the survivorship of aphids may be further reduced this spring. This may be good news for North Dakota because many of our soybean aphids migrate into North Dakota and this may slow development of aphid populations in soybeans. Time will tell.

[Source: Illinois Bulletin 7, Mike Gray]



The US Environmental Protection Agency requires all farmers who use Bt crops to plant at least 20-percent of their corn acreage to a refuge as part of an Insect Resistance Management (IRM) plan. The aim of this strategy is to provide an ample supply of insects that remain susceptible to the Bt toxin. The non-Bt refuge will decrease the odds that a resistant insect can emerge from a Bt field and choose another resistant insect as a mate. By preventing the pairing of resistant genes, these refuges help ensure that susceptibility is passed on to offspring.

To implement EPA’s IRM refuge requirement, the Bt corn registrants (e.g., Monsanto, Dow AgroSciences, Syngenta, and Pioneer Hi-Bred) enter into a contractual agreement with every farmer who buys Bt corn that obligates the farmer to plant the appropriate refuge. EPA also requires the Bt corn registrants to establish a compliance assurance monitoring program (CAP) to identify and address noncompliant farmers. If a farm is found to be out of compliance, a grower will receive a warning from the seed company. If the farm is out of compliance for a second year, the seed company will refuse to sell Bt corn to the grower. Field inspections may be performed by seed companies through the compliance assurance monitoring program. The purpose of the IRM refuge requirement is to maintain efficacy of Bt crops as an insect pest management tool by preventing or delaying development of insect resistance to these traits.

The following table lists the IRM refuge requirements contained in the "grower agreement" (also called "stewardship agreement") signed by each grower at the time of purchase of Bt corn seed. Please consult the grower guide/product use guide from your seed company for full details.


US EPA. 2005. Bacillus thuringiensis Cry3Bb1 Protein and the Genetic Material Necessary for its Production (Vector ZMIR13L) in Event Mon 863 Corn & Bacillus thuringiensis Cry1Ab Delta-Endotoxin and the Genetic Material Necessary for its Production in Corn (006430, 006484) Fact Sheet.

YieldGard® 2007 IRM Guide.

Product Use Guides for Hybrids with Herculex® and YieldGard® Traits

[Source: Wisconsin Pest Mgmt. News, Eileen Cullen]



Lepidopteran Registrations

Corn Rootworm Registrations

Stacked Lepidopteran + Corn Rootworm Registrations

Insect Pests Controlled

European corn borer, southwestern corn borer, sugarcane borer, southern corn stalk borer (corn earworm & fall armyworm suppression only)

Northern, Western and Mexican corn rootworm

See previous two columns


YieldGard® Corn Borer, Herculex® I

YieldGard® Rootworm, YieldGardVTO Rootworm, Herculex® RW, Agrisure® RW

YieldGard® Plus, YieldGardVT® Plus, Herculex® XTRA, Agrisure® CB/RW

Percent of acres planted to Bt corn




Percent of acres planted to corn refuge (not containing any Bt corn)




Location of corn refuge

Within ½ mile, on same farm and managed by same grower. Within field refuge configuration options include a large block refuge, split planter to alternate four or more rows of non-Bt Lepidopteran corn, or plant the field perimeter four or more rows wide to meet the 20-percent refuge.

Must be planted within or directly next to each Bt corn rootworm field. The corn rootworm refuge cannot be separated by another field, it does not have the distance flexibility of the corn borer refuge.

Within field refuge configuration options include a large block refuge, split planter to alternate four or more rows of non-Bt corn rootworm corn, or plant the field perimeter four or more rows wide to meet the 20-percent refuge.

Two different refuge options include:

Common Refuge: Must be planted within or directly next to each Bt corn rootworm field. The refuge cannot be separated by another field, it does not have the distance flexibility of the corn borer only refuge.

Separate Refuge: Plant a separate refuge to corn borers and a separate refuge for corn rootworms. See Lepidopteran and corn rootworm refuge requirements for each.

Treat refuge with insecticide



















The refuge corn can be treated with insecticide only when the level of pest pressure meets or exceeds economic threshold, and foliar Bt microbial sprays cannot be applied in the refuge.

The corn rootworm refuge can be treated for control of corn rootworm larvae and other soil insect pests with soil-applied, seed-applied or foliar-applied insecticides. The corn rootworm refuge can be treated with a non-Bt foliar insecticide to control late season pests such as corn borer. However if adult corn rootworm (beetles) are present at this time, then the Bt corn rootworm hybrid field must be treated in a similar manner.

Common Refuge: The common refuge can be treated with a soil-applied, seed-applied, or foliar-applied insecticide to control rootworm larvae and other soil insect pests. The common refuge can also be treated with a non-Bt foliar insecticide for late season pests such as European corn borer, if pest pressure reaches economic threshold. However, if rootworm adults (beetles) are present at the time of foliar applications then the stacked Bt corn field must be treated in a similar manner.

Separate Refuge:

1) Corn Borer Refuge: The corn borer refuge can be treated with a soil-applied or seed-applied insecticide for corn rootworm larval control or other soil insect pests. The corn borer refuge can be treated with a non-Bt foliar insecticide if economic thresholds for late season pests such as corn borer are met; the stacked Bt corn hybrid would NOT have to be treated in a similar manner under this option.

2) Corn Rootworm Refuge: The corn rootworm refuge can be managed for corn rootworm larvae and other soil insect pests using a soil-applied, seed-applied, or foliar-applied insecticide. The corn rootworm refuge can be treated with a non-Bt foliar insecticide for control of late season pests such as corn borers if pest pressure reaches economic threshold. However, if rootworm adults are present at that time, then the stacked Bt hybrid field must also be treated.

Other limitations

One type of Bt lepidopteran corn hybrid (e.g. YieldGard Corn Borer) cannot serve as a refuge for another group (e.g. Herculex I).

If the corn rootworm refuge is planted on rotated ground, then the Bt corn rootworm hybrid must also be planted on rotated ground. If the refuge is planted in continuous corn, then the Bt corn rootworm corn may be planted on either continuous or rotated ground.


Janet Knodel
Extension Entomologist



North Dakota State University Sugarbeet Entomologists and American Crystal Sugar Company have teamed up to provide much more extensive sugar beet root maggot fly count numbers than have been available for over 10 years. Drier growing season conditions increased the survival of sugarbeet root maggot larvae in 2006. Limited fly survey work and field damage ratings in 2006 documented a buildup of the root maggot population in several new hotspot areas.

New hotspots are likely in Polk, Traill, Norman, Cass, and Clay counties for 2007. Go to the American Crystal Sugar Company website, (http://www.crystalsugar.com/agronomy/agtools/pest/) for a detailed map showing these locations. At this website you will also be able to view detailed maps of all fields being monitored for fly populations. Maps will show daily and cumulative seasonal fly count numbers. Posting of fly counts will begin about May 18, and will continue through the root maggot fly activity period. Management strategies developed by Dr. Mark Boetel, NDSU sugarbeet entomologist, dictated by these fly count numbers are also posted on the site.

A short Powerpoint presentation discussing root maggot management is also posted on this part of the website. For assistance with questions regarding root maggot management in your area, contact your agriculturist.

This effort to provide much more detailed information for root maggot management is supported by grants from the Sugarbeet Research and Education Board of MN and ND and American Crystal Sugar Company.

Allan Cattanach
General Agronomist
American Crystal Sugar Company



Root maggot. Newly emerged sugarbeet root maggot flies were observed by NDSU personnel in southern Pembina County of North Dakota on May 15. This is somewhat earlier than most years, and suggests that peak activity in beet fields could occur earlier than normal this year; however, soil and air temperatures during the next few weeks will affect the timing of peak activity.

Soil and ambient (air) degree-day (DD) accumulations are run on the NDSU root maggot development model each year to forecast the timing of key events in the insect’s life cycle. Soil temperatures affect maggot developmental rates from larvae through pupae, and into the adult stage. Once the insects have emerged from soil as adults, ambient DD accumulations are used to predict when fly activity will peak in this year’s beet fields.

Peak emergence usually occurs when old (last year’s) beet fields reach 450 soil DD (bare soil at 4" depth). As of the latter part of this week, soils ranged widely from about 175 DD at the St. Thomas NDAWN station to 290 at Baker, MN. Accumulations will likely range between 14 and 22 DD units per day, depending on location, and will increase over time during the next couple of weeks. Thus, it will probably take an additional 8 to 18 days for most area fields to reach the 450 DD required for peak emergence from previous-year beet fields.

Peak activity in new (current-year) beet fields usually occurs between 4 and 10 days after peak emergence from old beet ground. Its timing is also affected by temperature and, at the earliest, will coincide with the accumulation of 600 ambient DD units. Although it is too early to accurately predict, it is possible that significant levels of fly activity could begin occurring during the first week of June in southern portions of the Red River Valley, and major activity will most likely begin about 7 to 10 days later in northern reaches of the Valley. Cool, windy, or rainy weather can reduce or delay fly activity because the insects avoid flight during such conditions. Warm (80 degrees Fahrenheit or above) daytime weather is usually needed for the actual peak to occur. Therefore, the extended weather forecast must be considered when trying to anticipate peak fly activity timing. Infestations of 1 or more flies per plant in sugarbeet fields may be economically justifiable to require a postemergence insecticide application. Vigilance in applying postemergence materials to manage the root maggot in these areas could also help combat the development of damaging populations in these areas for next year.

Cutworms. Scattered reports of cutworm infestations have been reported from southern and central portions of the Red River Valley. Be on the lookout for wilting and cut seedlings. Cutworms can range in size from 5/16 to 1½ inch long, and several species damage sugarbeet. Larvae are most active in early morning and evening, but can be found during daylight hours by sifting through the upper 2 inches of soil around seedling plants. Chemical control is recommended if 4 to 5% of seedlings are showing injury. Early evening is a good time to apply liquid insecticides to manage cutworms because they will be actively feeding soon after the application.

Flea beetles. Early spring is the most likely time that flea beetles can cause economic injury to sugarbeet. Injury occurs as tiny "shot-holes" on seedling leaves, and severe infestations can cause major stand losses. Flea beetles are shiny shell-winged beetles that are usually about 1/6 inch long. Their most distinguishing feature is a pair of enlarged hind legs, which enables them to jump in a manner similar to that of a flea or grasshopper when disturbed. The greatest risk of flea beetle damage is in sugarbeet fields that follow alfalfa or beans, or fields that had outbreaks of broadleaf weeds. Fields should be treated if the infestation threatens to reduce the plant population below 35,000 per acre. Most foliar liquid insecticides labeled for use in sugarbeet should do a good job of controlling flea beetles.

Defoliating weevil. The leaf-feeding weevil, Tanymecus confusus, is a sporadic pest of sugarbeet in the Red River Valley. Adults are about ½ inch long. They are mottled brownish-gray in color, and have broad snout-shaped heads. Their host plants include several broadleaf weeds). Weevils damage sugarbeet during May and early June. Adults use chewing mouthparts to feed on cotyledons and leaves of young seedlings. Most damage occurs along leaf edges and interveinal areas, but the midribs are usually left intact. Significant feeding damage can result in seedling death. Currently, no specific insecticide is labeled to manage this insect; however, most liquid products labeled for use on sugarbeet are likely to provide adequate control.

For specific information on managing insect pests of sugarbeet, please refer to the "Insect Control" section of the 2007 Sugarbeet Production Guide or the "Sugarbeet Insects" section of the 2007 Field Crop Insect Management Recommendations. The respective WWW locations for online versions of these publications are:




Mark Boetel
Research & Extension Entomologist

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