Pest & Crop

Purdue Cooperative Extension Service
March 5, 2007

Pest & Crop Newsletter, Entomology Extension, Purdue University

In This Issue
Purdue Extension Feild Crop Specialists
Insects, Mites, and Nematodes

Winter Temperatures and Field Crop Insects – (John Obermeyer, Christian Krupke, and Larry Bledsoe)

  • Temperature is just one factor that impacts an insect’s winter survival.
  • Spring temperatures and moisture generally have a greater influence on insect numbers and subsequent crop damage.
  • Production practices, such as date of planting, tillage type, and herbicide application, are often what makes or breaks an insect infestation.

We’ve had a cold and snowy December, mild January, but February has been a roller-coaster ride. Will this equate to more/fewer insects and greater/reduced crop damage this coming season? As you probably already guessed…it depends! Although we can’t tell you for sure what will happen with these critters coming out of this winter, we can give you some information on insect/environment/crop interactions that might clear the picture somewhat.

Winter conditions, December to mid-February

Overwintering insects utilize various behavioral and physiological mechanisms to keep them from dying during the long winter months. Survival tactics include, but are not limited to: lowering metabolic rates, chemical changes in bodily fluids, and finding “cozy” microenvironments.

Predictive models for some overwintering insects exist but it is impossible to measure all of the environmental variables that individual insects are subjected to in their overwintering locations. The graph below compares ambient air and 4”soil depth temperatures with snowfall recorded at the Agronomy Research Center in West Lafayette for twelve winters. This depicts how soil temperatures tend to follow air temperature trends. However, as snowfall amounts decrease, the temperature differential is less between the air and soil (e.g., 2002, 1998). It comes as no surprise that snow cover provides an insulating blanket for overwintering insects at or below ground level. Though the differences may seem minor to us, to a small, cold-blooded insect, it may make the difference between life and death.

Above Ground Insects:

Bean Leaf Beetle

Bean Leaf Beetle. 1997-2005, Soybean Sweeps

Corn Flea Beetle

European Corn Borer

Black Cutworm

Alfalfa Weevil

Below Ground Insects:

Rootworm Risk Areas

Western Corn Rootworm

White Grubs

Japanese Beetle Populations. 1997-2005, Soybean Sweeps

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Rootworm Insecticide Classifications and Consistency of Performance - (Christian Krupke, Larry Bledsoe and John Obermeyer)

  • The following table lists registered rootworm soil insectticides by chemical class.
  • Follow label uses and restrictions.
  • Many factors should be considered before selecting a product.

See the following table “Factors to Consider when Choosing a Product for Corn Rootworm Protection”.

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Nematode Update- Seed and Soil Testing Available for Soybean Cyst Nematode - (Jamal Faghihi and Virginia Ferris)

  • Some SCN resistant soybean may no longer be effective in infested fields.
  • Testing the field's soil for SCN and resistance of intended cultivars is available at a nominal fee.
  • Samples submitted soon can be completed before 2006 planning.

As we eagerly wait for another planting season to begin, most producers have decided on what soybean cultivars they are going to plant. Where problems have occurred with soybean cyst nematode (SCN) in the past, they have probably chosen one or more of the “cyst-bean” cultivars to plant. Our recent field observations have shown that some of these cultivars may no longer be as effective as desired. To allow producers to check this situation and to make prudent SCN management decisions, we provide a service to check in the greenhouse the degree of resistance for these resistant cultivars.

Shown in red are counties with confirmed infestation of soybean cyst nematode in Indiana
Shown in red are counties with confirmed infestation of soybean cyst nematode in Indiana.

The test requires about a gallon of infested field soil and about 100 seeds from each cultivar intended to be planted in a given field, we then expose those seeds to SCN extracted from the field soil and provide the resistance data. If there are enough SCN in the soil that you provide, this process will take about 6 weeks to complete and cost about $50 for up to five soybean cultivars. We charge $10/each additional cultivar. We also perform a race test, for an additional $50/test.

There is still time to perform any of these tests for the upcoming growing season, assuming we are able to extract enough SCN from your soil to conduct the test. If SCN are lacking in your field soil sample, we have to increase them in the greenhouse. This additional task will add another 6 weeks time to the process and add $20 cost/sample.

The best way to manage SCN is to monitor populations by sampling each field at least every 4 years. You can observe the white or yellow females on the roots only during the growing season, but you can sample the soil anytime of the year and get an accurate account of the SCN population. This is a very crucial step in SCN management and should not be neglected. As we mentioned in our articles late last year, the Indiana Soybean Board has decided to no longer pay for the soil processing fee as of January 1, 2006. However, we will continue to provide this service to growers at the cost of $10/sample, for which the submitter will receive an invoice unless we are instructed otherwise.

A broken cyst revealing hundreds of eggs inside.

A broken cyst revealing hundreds of eggs inside

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Click here to see table:
Factors to Consider When Choosing a Product for Corn Rootworm Protection



Can Proactive Herbicide Resistance Management Pay? – (Chris Boerboom, Ext. Weed Scientist and Paul Mitchell, Ext. Ag. Economist, University of Wisconsin)

Additional cases of glyphosate-resistant weeds in the Midwest should have Wisconsin growers thinking about management options to delay or prevent resistance.  However, most growers probably think the options will cost more money compared to using low cost glyphosate in Roundup Ready crops.  They might be right.  But on the other hand, a glyphosate-resistant weed might be expensive to control in the future too. So in regards to resistance management, the question is: Is it more profitable to pay now or to pay later?

Another way to consider this question is to ask if a grower wants to wait until a resistant weed problem develops and react at that time by adding another herbicide or switching to a different herbicide.  Reactive management is like “using a tool until it breaks, then finding a new tool”.  It is reasonable to assume that the cost of weed control will increase after resistance develops because an additional herbicide will be needed or weed control may not be as good.  In addition, yield losses may occur during the year or two when glyphosate fails to control the weed and other herbicide options are applied too late to achieve adequate control. 

Alternatively, a grower could be proactive and use options to delay resistance.  This would be like “using a tool carefully so it doesn’t break”.  Proactive management likely increases the current cost of management if the tactics used to delay resistance include herbicide tank mixtures or preemergence herbicides.  Even herbicide rotations may increase short-term costs depending on the herbicide programs used.  However, this increased short-term cost comes with the benefit of lower costs in the long run because resistance does not develop.

The economic choice between these two strategies depends on the number of years that it takes for resistance to develop, the cost of the options, the cost of controlling the resistant weed after it develops, and the interest rate.  With this information, the most profitable choice can be calculated.  Reactive management is most profitable if resistance is not likely to occur for a long time into the future.  However, investing in proactive management makes sense if the cost of controlling a herbicide resistant weed is high.

Examples of these economic choices are summarized in the following table based on a paper by Mueller and others (2005).  Consider these examples.

  1. If it costs $10/a for a more expensive herbicide rotation to be proactive and it only costs an extra $2.50/a to add a tank mix partner to control a glyphosate-resistant weed, proactive management would never pay.
  2. If the proactive option only costs an extra $2/a and the extra cost to control the glyphosate-resistant weed is only $2.50/a, the resistance would have to happen very soon (within 3 years) for the proactive management to pay.
  3. If the proactive option only costs an extra $2/a, but the extra cost to control the glyphosate-resistant weed is very expensive ($20/a), the extra $2/a would be money well spent even if the glyphosate-resistant weed didn’t develop for 29 years.

Proactive management pays if resistance occurs before the number of years listed in the table.

Additional annual cost to conrol the glyphosate- resistant weed
Additional annual cost for proactive management
3 yr
11 yr
3 yr
20 yr
11 yr
6 yr
3 yr
29 yr
20 yr
15 yr
11 yr
9 yr
This example assumes a discount rate of 8%.

This suggests that weeds that are currently difficult or expensive to control without glyphosate , such as waterhemp, giant ragweed, and perhaps common lambsquarters, may be the best targets for proactive management.

Perhaps a more realistic way to consider these options and costs is to use an example with glyphoste-resistant waterhemp.  In the next table, we outlined weed management programs with four levels of resistance management that ranged from none to quite high.  These examples suggest that glyphosate-resistant waterhemp may be one of those weeds that could be very expensive to control.  Plus, we think it suggests that there are cost effective, proactive options that can be used such as using preemergence herbicides or rotating glyphosate with other herbicide modes of action.  (Note that no additional costs are included to control volunteer RR corn in the soybeans if required.)

Cost of weed management programs considering potential glyphosate-resistant waterhemp.

Low cost program that has high risks for selecting glyphosate-resistant weeds and high risk of yield loss because of poorly timed applications; not recommended

  RR corn/glyphosate/application
  RR soybean/glyphosate/application
    Average accross rotation

Program that reduces risks of resistance and yield loss by adding a pre herbicide in corn
  RR corn/Harness/glyphosate/2 applications
  RR soybean/glyphosate/application
    Average accross rotation
Program that further reduces risk of resistance by rotating herbicide modes of action in the corn year
  Conv. corn/Lumax/application
  RR soybean/glyphosate/application
    Average accross rotation
Program with the most proactive management; herbicide rotation plus a pre herbicide before glyphosate in soybean
  Conv. corn/Lumax/application
  RR soybean/Valor/glyphosate/2 applications
    Average accross rotation
Program that may be required to control glyphosate-resistant waterhemp in Roundup Ready crops
  RR corn/Harness/glyphosate+Clarity/2 applications
  RR soybean/Valor/glyphoste+Cobra/2 applications
    Average accross rotation
Prices assumed. The herbicides and prices are just used as an example.  You can adjust the prices and herbicides based on your situation to make more accurate comparisons.
      Roundup Ready corn (extra $20/bag)
      Roundup Ready soybean (used in all examples)
      custom application
      preemergence Valor at 2 oz/a
      preemergence Harness at 1.5 pt/a
      preemergence Lumax at 3 qt/a
      postemergence Clarity at 1 pt/a
      postemergence Cobra at 8 oz/a
Source: Mueller, T. C., P. D. Mitchell, B. G. Young, and A. S. Culpepper. 2005. Proactive versus reactive management of glyphosate-resistant or –tolerant weeds.  Weed Technol. 19:924-933.

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Telephone, E-mail Addresses and Specialty
Yaninek, Steve (765) 494-4554 Head, Dept. of Entomology
Bledsoe , Larry (765) 494-8324 Field Crop Insects
Hunt, Greg (765) 494-4605 Bee Specialist
Krupke, Christian (765) 494-4912 Field Crop Insects
Lam, Frankie (812) 886-0198 Insect Pest Management, SWPAC
Loven, Judy (765) 494-8721 USDA, APHIS, Animal Damage
Mason, Linda J. (765) 494-4586 Food Pest Mgmt. & Stored Grain
Obermeyer, John L. (765) 494-4563 Field Crop Insects & IPM Specialist
Tammy Luck (765) 494-8761 Administrative Assistant
FAX: (765) 494-2152

Dept. Web Site:

Beyrouty, Craig (765) 494-4774 Head, Dept. of Agronomy
Brouder, Sylvie (765) 496-1489 Plant Nutrition, Soil Fertility, Water Quality
Camberato, Jim (765) 496-9338 Soil Fertility
Conley, Shawn (765) 494-0895 Soybeans, Small Grains, Specialty Crops
Gerber, Corey (765) 496-3755 Director, Diagnostic Training Center
Joern, Brad (765) 494-9767 Soil Fertility, Waste Mgmt.
Johnson, Keith D. (765) 494-4800 Forages
Mansfield, Charles (812) 888-4311 Small Grains, Soybean, Corn
Nielsen, Robert L. (765) 494-4802 Corn, Sorghum, Precision Agriculture
Steinhardt, Gary (765) 494-8063 Soil Mgmt., Tillage, Land Use
Vyn , Tony (765) 496-3757 Cropping Systems & Tillage
West, Terry (765) 494-4799 Soil Mgmt. & Tillage
Lisa Metts

(765) 494-4783 Extension Secretary
FAX: (765) 496-2926
Botany and Plant Pathology
Bauman, Tom T. (765) 494-4625 Weed Science
Johnson, William (765) 494-4656 Weed Science
Nice, Glenn (765) 496-2121 Weed Science
Rane, Karen (765) 494-5821 Plant & Pest Diagnostic Lab
Ruhl, Gail (765) 494-4641 Plant & Pest Diagnostic Lab
Shaner, Greg (765) 494-4651 Diseases of Field Crops
Westphal, Andreas (765) 496-2170 Soil-borne Diseases
Whitford, Fred (765) 494-4566 Purdue Pesticide Programs
Woloshuk, Charles (765) 494-3450 Mycotoxins in Corn
Amy Deitrich (765) 494-9871 Extension Secretary
FAX: (765)494-0363
Agricultural & Biological Enginerring
Engel, Bernie (765) 494-1162 Interim Head, Dept. of Ag. & Bio. Engr.
Ess, Daniel R. (765) 496-3977 Precision Ag., Ag System Mgmt.
Frankenberger, Jane (765) 494-1194 GIS and Water Quality
Maier, Dirk (765) 494-1175 Post Harvest Engineering
Mack, Strickland R. (765) 494-1222 Precision Farming Appl.
Carol Glotzbach (765) 494-1174 Extension Secretary
FAX: (765) 496-1356
Dept. Web Site: