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No. 00/August 11, 2000

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IN THIS ISSUE:
Welcome to the First 2000 Issue of the Bulletin
The Bulletin on the Web in 2000
What Can We Expect from Insect Pests Following Another Mild Winter?
Alfalfa Weevils Get an Early Start This Year
Status of Western Corn Rootworm Densities in Soybean Fields in 1999: Outlook for Larval Injury in Rotated Cornfields for 2000
Secondary Insect Pests in Corn: The Watch Begins
Anticipating Wireworm Problems This Spring
New Products for Control of Soil Insects in Corn: Buyer Beware
Standardized Resistance Management Recommendations for Bt Corn in 2000
1999 WPS Compliance Inspection Results
New Herbicides for 2000
Thanks, Mac
Corrections for the 2000 Illinois Agricultural Pest Management Handbook
Is Herbicide Carryover a Concern for 2000?
Planting Corn--How Early Is Too Early?
Useful References from the Entomological Society of America
Reports of Intense Captures of Black Cutworm Adults
Corn Flea Beetle: Expectations for Injury in 2000
Insect Resistance Management for Bt Corn
Alfalfa Weevils Still Active
Pea Aphids Found in Alfalfa Fields
Winter Wheat Disease Update
Be Alert for Corn Nematode Problems
Soybean Seed Treatments for 2000
Herbicide Formulations and Calculations: Active Ingredient or Acid Equivalent?
Glyphosate Options for Glyphosate-Resistant Soybeans
Principles of Soil-Applied Herbicides
A Sea of Purple
Balance and Epic Label Changes for 2000
Still Cold and Dry: What About Corn Planting?
Regional Updates
The Watch for Black Cutworms Will Intensify
Section 2(ee) Recommendation for Warrior T
White Grubs: Expectations and Management Recommendations for 2000
Free Sticky Traps Still Available!
Update on Alfalfa Weevils
Opening Day Approaches: The University of Illinois Plant Clinic Reopens May 1, 2000
Stewart's Bacterial Wilt and Flea Beetles
Corn and Soybean Herbicide Premixes
Herbicide-Resistant Weeds: Where Are We in Illinois?
Correction (and More) on Planting Depth
Regional Reports
Captures of Black Cutworm Adults: What Type of Trap Do You Have?
Soil Insecticide Performance for 2000: Will Anticipated Dry Weather Have an Effect?
Alfalfa Weevil Situation
Clover Leaf Weevils Causing Damage in Some Alfalfa Fields
Aphids in Alfalfa: Some Clarification
Wheat Streak Mosaic in Winter Wheat
IPM Approach for Managing Soybean Cyst Nematode
Proper Handling of Soil Samples for Nematode Analysis
Knowing When to Look for Weeds
Corrections from Issue 2 of the Bulletin
Thinking About Nitrogen Recommendations
Will Starter Fertilizer Increase Corn Yield?
Regional Update
Projected Cutting Dates for Black Cutworms
A Consultant's Observations from the Field
First Observation of Southern Corn Leaf Beetles
Spraying for Control of Alfalfa Weevils in Central Illinois
Wheat Streak Epidemic in Illinois Wheat Crop?
Pythium Seedling Blight Potential
Considerations for Early-Season Weed Control in Corn
Regional Updates
Scouting Update Workshop
Voluntary "Subscriptions" to the Bulletin on the Web
Early-Season Insects Having a Heyday in Some Cornfields
Black Cutworms Are Cutting Corn Plants in Southern Illinois
More Information About the Southern Corn Leaf Beetle
Replanting Necessitated by White Grub and Wireworm Damage, and a Note About Grape Colaspis
Wheat Producers: Cereal Leaf Beetles Are Hard at Work
Current Alfalfa Weevil Situation
Newer Nozzles for Drift Management
Wheat Problems Continue to Expand
Soil-Applied Herbicides for Soybeans
Annual Bluegrass and Butterweed
Nitrogen Loss in 2000
Regional Reports
Southern Corn Leaf Beetle Has Caused Significant Damage in Western Illinois
European Corn Borer Moth Emergence Under Way in Southern Illinois
Watch for Stalk Borers Soon
Bean Leaf Beetles: Expectations for This Growing Season
Status of Alfalfa Weevil and Presence of Natural Enemies
Wheat Diseases Continue to Cause Problems
Take-All on Wheat Crop
Stewarts' Wilt Killing Corn Seedlings
Principles of Postemergence Herbicides
Postemergence Corn Herbicides--Some Precautions to Consider
Corn Off to a Good Start
Regional Reports
Mark Your Calendars Now for the 2000 University of Illinois Agronomy Day--August 24
Report from the Field
An Update on Soil Heat-Unit Accumulations and the Corn Rootworm Larval Hatch
Bean Leaf Beetle Populations Reach Impressive Levels in Early-Planted Soybeans
So, Again with Grape Colaspis?
Stalk Borers Are Active
Billbugs May Cause Problems in Some Fields
Reports of Armyworms in Wheat and Corn
Bean Pod Mottle Virus: Hook, Line, and Sinker?
FMC Receives Label for Command Xtra
Post Now, Continue Scouting Later
Regional Reports
UPDATE: Corn and Early Growth Problems
UPDATE: Flexstar Carryover Symptoms on Corn
Corn Rootworm Hatch Under Way
European Corn Borer Moths Observed in Western Illinois
Stalk Borers on the Move
Grape Colaspis and White Grubs Remain Active
Don't Forget to Scout Alfalfa Fields for Regrowth
Potato Leafhoppers Can Be Found Statewide
East-Central Region IPM Update
High Tech Pest Diagnostics
Flexstar Carryover Symptoms on Corn
Soybean Injury from Sulfentrazone
Postemergence Herbicide Options for Grass Control in Corn
Corn Development
Ammonia Injury
Nitrogen Loss in Illinois in 2000
Regional Reports
UPDATE: Seedling Blights and Seed Decay of Soybean
Preliminary Results from Grape Colaspis Insecticide Efficacy Trial
Don't Forget to Scout for First-Generation European Corn Borer
Southwestern Corn Borer Moths Common in Southern Illinois
Continue Monitoring Soybean Fields for Bean Leaf Beetles and Alfalfa for Stubble Injury
Regional Reports
Armyworm Reports Continue in Cornfields and Wheat Fields
Stay Tuned for Potato Leafhopper Infestations to Intensify
Update on Corn Rootworm Development
Last Warning of the Season for Stalk Borer Movement into Northern Illinois Cornfields
Grasshopper Numbers Increasing
Weak First Flight of European Corn Borers Persists
Insecticide Efficacy Results for White Grubs
Watch Those Beans for Spots and Rots
Drift Complaints: What You Should Know
Aim Herbicide Injury to Corn
Preharvest Weed Control in Wheat
Regional Reports
Corn Rootworm Larvae Commonly Found in Many Cornfields
First Flight of European Corn Borer Persists at Low Levels
Effect of Bt Corn on Nontarget Insects: The News Isn't All Bad
Corn Viruses and Thrips
Maize Chlorotic Mottle
Update on Stewart's Bacterial Wilt
Corn Charges Ahead
Regional Reports
Grape Colaspis Story Changes Chapters
Many people throughout central Illinois will remember 2000 as yet another year when grape colaspis larvae caused economic damage to corn. We still know very little about the biology and behavior of these insects, and management options are few and far between. We would like to keep track of when grape colaspis adults move into soybeans. If you find grape colaspis adults on yellow sticky traps, in sweep nets, or simply by observation, please let us know.

Corn Rootworm Adults Are Emerging
Rootworm development this year is a bit ahead of schedule, so it's not too soon to start watching for both northern and western corn rootworm adults throughout the state. The article discusses two reasons to scout for rootworm adults in corn: to watch for silk-clipping injury that interferes with pollination and to assess the potential for injury in corn in 2001.

Evaluating Corn Roots for Rootworm Damage
From mid-June through early July, many growers, dealers, consultants, and seed and pesticide company representatives spend some time roaming through cornfields, digging up root systems, and looking for corn rootworm larvae and signs of their feeding injury. Appropriate interpretation of what you find is important.

The article presents the best procedure for sampling for rootworm larvae and assessing root damage. We think it is more prudent to assess performance of an insecticide by evaluating the amount of damage to the root system.

The article also addresses "rescue" treatments for cornfields with rootworm larvae and rootworm damage.

Status of European Corn Borers
The amount of injury being caused by corn borers in southeastern counties this year is greater than the amount of injury being caused in northwestern Illinois. It is usually the other way around, although the presence of southwestern corn borers in southern Illinois changes things a bit. As it stands right now, we probably will not experience many problems with first-generation European corn borers this year. Nevertheless, when adults that will lay eggs for the second generation begin emerging in July, we'll keep you apprised.

Spider Mites in Soybeans in Some Dry Areas of the State
For those of us in areas of the state that have been inundated with rain, talk about twospotted spider mites in soybeans seems silly. However, in the dry areas in western Illinois, spider mites have begun to make their presence known.

Management of twospotted spider mites in soybeans depends greatly on vigilance. At the first sign of injury caused by spider mites, you should examine the injured area to look for the mites. If you find spider mites only in field edges, spot treatments to prevent additional damage and to halt their movement may be justified. However, you should make certain that spider mites are not present throughout the field.

Soybean Leaf Cupping/Puckering
While the 2000 growing season has been relatively favorable for soybean development and has also allowed for timely applications of postemergence herbicides, the leaf-puckering phenomenon has again appeared. This article presents several theories that have been put forward by weed scientists across several states in the north central region, including the following:

1. Somehow, the plants have been exposed to a growth regulator herbicide. 2. The soybean plant is expressing a physiological response to somewhat adverse growing conditions. 3. The response is induced by a postemergence herbicide application.

Note that it is very unlikely that only one of these possibilities will explain the cause of puckered soybeans in all instances.

The available literature tends to suggest that this type of injury does not always necessarily result in soybean yield loss, but several factors are involved in determining if yield loss will occur, such as soybean variety, time of exposure, and dosage.

Maximum Weed Sizes for Post-emergence Soybean Broadleaf Herbicides
Surplus rainfall, hot temperatures, and some delayed soybean planting have all combined to create significant broadleaf weed problems in many soybean fields. One "good" point with respect to past and current environmental conditions is that the weeds have not been under moisture stress conditions and are relatively "soft." This may translate into better activity from many post-emergence broadleaf herbicides. Unfortunately, the soybeans are also "soft," which increases the likelihood for crop response following the postemergence herbicide application.

The article includes a table that contains maximum broadleaf weed sizes as indicated on several postemergence soybean herbicide labels.

Postemergence Soybean Herbicide Injury: Is There a Yield Penalty?
Postemergence herbicide applications for weed control in soybeans are nearly completed in some areas of Illinois. Depending on the herbicide applied, some of these recently treated soybean fields are easily identified from a "windshield survey"; due to the large amount of soybean injury. The Soybean Research and Development Council worked in conjunction with the University of Illinois, Southern Illinois University, and Iowa State University to conduct research trials on evaluating the effect of postemergence herbicides on soybean yield. The article answers these questions:

What type of soybean injury was experienced?
Did injury reduce soybean yield?
What is the bottom line?

According to the study, injury from postemergence herbicides is not a good predictor of soybean yield loss.

Wheat Crop "Season Finale"
Wheat headed about a week to 10 days early in most areas, and with the warm temperatures in the past month, it has also filled grain and ripened earlier than usual. Nearly all of the wheat in the southern half of the state has reached physiological maturity, and the main problem now is wet soils that both keep the grain above ideal harvest moistures and also keep combines out of the field.

As all wheat producers know from painful experience, harvest delays due to wet weather usually decrease the quality of wheat. On the other hand, remember that wheat grain can lose moisture very fast (up to five or six points per day), and so the time gained by harvesting at high moisture may be minimal.

Corn Keeps Up the Pace
At its current rate of development, I expect most of the corn planted in April in central Illinois to reach tasseling by late June and early July. Records for early development are being broken this year. The corn crop in southern and northern Illinois is somewhat behind in development, due both to later planting and to cooler temperatures in the northern areas.

Regional Reports
Extension center educators, unit educators, and unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season.

This week's issue includes reports from northern Illinois and west-central Illinois.

Get Ready for Rootworm Adults
More reports regarding emergence of adult western and northern corn rootworms came in during the week of June 26, so we can assume that emergence will be in full swing all over the state within the week. The presence of emerging adults also means that larvae are completing their development, and the amount of root damage in any given field will be at its zenith soon.

You can begin assessing corn roots for rootworm larval damage right now. As pollination begins in various regions of the state, you should be alert for large numbers of rootworm adults. If they clip enough silks, they can interfere with pollination.

This article lists suggested insecticides for control of corn rootworm adults.

Field Day Scheduled to Promote Western Corn Rootworm Monitoring Program
In 1998, University of Illinois Extension entomologists unveiled a monitoring program for adult western corn rootworms (WCR) in soybean fields to predict root injury in rotated corn. The monitoring program is in its third year, and data from this program have shown the new strain of western corn rootworm is now present in 26 counties in Illinois. To learn more about this monitoring program, growers are invited to attend a field day: July 7, Arthur, Illinois; July 13, Petersburg, Illinois; and July 14, Bloomington, Illinois.

First Report of Japanese Beetles
Many of us will remember the very large numbers of Japanese beetles that occurred in corn and soybeans last year, especially in eastern and central Illinois. We need to be ready for them again because early indications suggest they may be numerous in 2000.

Japanese beetles have been reported around homes and gardens in most of the major cities in Illinois. Therefore, we should anticipate that they will show up in nearby crop fields and possibly spread from there.

The greatest concern regarding Japanese beetles is their feeding on soybean foliage. Although no one has reported finding Japanese beetles in soybean fields yet, you should be aware of the threshold, just in case the beetles show up in soybeans soon.

Corn Leaf Aphids in the Whorls of Corn Plants
Winged corn leaf aphids have been found in the whorls of corn plants across a wide area in the northern half of Illinois during the week of June 26. They might have been recently blown into Illinois on the storm fronts that have passed through. Large numbers of corn leaf aphids are usually associated with droughty conditions, which certainly do not exist in most areas of Illinois. However, corn leaf aphids are capable of increasing their numbers dramatically.

Status of First-Generation European Corn Borers
We still have heard very little in the way of significant numbers of first-generation European corn borers in 2000.

For the most part, the first generation of the European corn borer will come to an end soon in southern Illinois. But don't be lulled to sleep; the second generation still deserves our attention.

Plenty of Southwestern Corn Borers in Some Counties
Recent mild winters have allowed the southwestern corn borer to thrive in our southern counties, and it has caused far more concern than the European corn borer. Numbers of southwestern corn borers this year are fairly large in some areas.

Entomologists debate whether first-generation southwestern corn borers cause economic damage. But regardless of your take on this issue, the second generation of this important insect pest is worth your attention if you live or work south of I-70.

Wheat Streak Mosaic Virus in Field Corn
Shawn Kaeppler (from the University of Wisconsin) and others recently published some work looking at the interaction of wheat streak mosaic virus (WSMV) and high plains virus (HPV). In the study, they looked at the virus symptom development and how well the virus replicated in the plant for each virus singly and in combination.

Most of our currently grown hybrids do not have susceptibility to the virus, but some inbreds do. And the study showed that the virus replicated well in the tissue despite the absence of lethal symptoms.

Two things could happen. First, the corn can serve as a green bridge to keep the virus around until the winter wheat is planted. Second, if either maize chlorotic mottle virus (MCMV) or high plains virus (HPV) should by some unfortunate circumstance move their way into the state, some very "lethal" damage can develop on the corn if the corn plants are acting as a nonsymptomatic host for WSMV.

Fungal Leaf Disease Showing Up in Corn
Common rust on field corn is here. It seems that about every 5 or 6 years it shows up early in the season in field corn and causes concern. We have reports of active common rust in the northwestern and west-central parts of the state.

How can you make a reasonable decision about treatment? First, consider the weather. Next, consider the probability of other fungal leaf blights developing in the field. You need to know the probability of other fungal diseases developing because there's not a big arsenal of fungicides for treatment.

Alert: Toxic Ergot Prevalent in Brome Grass and Rye This Year
Ergot is very prevalent along unmowed fencerows and in pastures this year. Ergot is a fungal disease of the seed head of about 200 wild and cultivated grasses and opened-pollinated small grains like rye.

Infested grain is a concern because the fungus produces very potent toxins that affect both humans and animals. Grasses should be inspected for ergot before allowing grazing this year.

Regional Reports
Extension center educators, unit educators, and unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season.

This week's issue includes reports from northern Illinois and west-central Illinois.

Evaluating Corn Roots for Rootworm Larval Damage
It's now time to talk about rating roots for rootworm damage. This article offers an explanation for the Iowa State University 1-6 root rating scale. Schematic illustrations of root ratings 2, 3, 4, and 5 are included, as well as a brief video of the root rating process.

Some cornfields in western Illinois are showing signs of severe rootworm larval damage. As July progresses, we may receive more reports of such damage. In fact, if rains continue to loosen the soil and if wind becomes a factor, some corn plants may lodge as a result of severe rootworm larval damage. However, always remember that other factors can cause corn plants to lodge; only by examining the roots can you verify the presence or absence of rootworm damage.

Western Corn Rootworm Field Days in McLean and Menard Counties
This article provides some additional information about the field days for the western corn rootworm monitoring program scheduled in McLean and Menard counties.

Japanese Beetle Densities Remain Impressive: Don't Forget to Monitor Fields for Silking Clipping
Like many of the other grub species that have plagued Illinois producers this spring, the Japanese beetle promises to be no exception. In the coming weeks of July, corn growers are urged to monitor their pollinating fields for Japanese beetle adults and their silk clipping activities. In August, producers will increasingly turn their attention to soybean fields and defoliation caused by this insect pest.

Scouting efforts should be well under way for Japanese beetle adults during this silking and pollination period of corn development.

Fungal Leaf Diseases on Corn
This article describes several fungal leaf diseases on corn, including common rust, southern rust, physoderma brown spot, anthracnose, and eyespot. What is important to remember about all these leaf blights, including the rusts fungi, is not the individual identity of which blight you have but rather the percentage of leaf area blighted as a whole on your entire plant; control considerations may be justified when whole-plant infection reaches 15%. Note that the type of symptoms or size and coloration of lesions for these corn leaf blights can vary with the genetic resistance of the hybrid that you plant.

What's Ahead for the Corn Crop?
In most areas of Illinois, rainfall has been adequate to allow the corn crop to approach pollination in good shape, with enough stored soil moisture to carry the crop through pollination and into the start of grainfilling. Although moderate temperatures the past 2 weeks have slowed the race toward pollination a little bit, many fields in the central part of the state are fully into the silking stage, and some have probably completed the pollination process.

A sudden onset of hot, dry weather can still cause some damage, especially to those crops that haven't yet tasseled. But if grainfilling starts early and takes place during warmer weather, it will also occur more rapidly, and physiological maturity should come early.

Regional Reports
Extension center educators, unit educators, and unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season.

This week's issue includes reports from northern Illinois and west-central Illinois.

University of Illinois Off-Campus Courses, Fall 2000
The Off-Campus Graduate Studies (OCGS) program offered through the Department of Crop Sciences enables students to continue the

The Off-Campus Graduate Studies (OCGS) program offered through the Department of Crop Sciences enables students to continue their education at many locations in Illinois. Students who enroll in the program may choose to participate in courses primarily to advance their own professional development, or they may seek admission to the master's degree program in the Department of Crop Sciences.

Off-campus courses that are offered this fall include Principles of Plant Breeding, Weed Management in Agronomic Crops, Fundamentals of Insect Pest Management, Plant Physiology, Diseases of Field Crops, Crop Growth and Development, and Herbicide Fate and Mode of Action in Plants.



Reports of Extensive Corn Rootworm Larval Injury Common
On July 13, we will begin to evaluate our experimental plots for corn rootworm larval injury

On July 13, we will begin to evaluate our experimental plots for corn rootworm larval injury. On July 7, John Shaw found 8 corn rootworm pupae, 5 pre-pupae, 16 third-instar larvae, and 12 second-instar larvae. Pete Fandel, crop systems educator, Woodford County, observed significant corn rootworm injury in cornfields near Minonk (northeast Woodford County).

Reports such as Pete's are becoming more common as we approach mid-July. But don't automatically assume that a lodged field has significant corn rootworm larval injury. And if significant root pruning is discovered, don't panic. Many corn hybrids are able to regenerate roots from mid-July to mid-August, especially with the excellent soil moisture reserves we have in some areas of the state.



Grape Colaspis Adults Numerous in Soybean Fields
Soybean fields in many areas of Illinois continue to be "blessed" with bountiful densities of grape colaspis adults

Soybean fields in many areas of Illinois continue to be "blessed" with bountiful densities of grape colaspis adults. We should not be surprised by these observations based on the extensive number of reports concerning grape colaspis larval injury earlier this summer.

If you're using Pherocon AM traps to monitor densities of western corn rootworm adults in your soybean fields, it may be a good idea to also keep track of the numbers of grape colaspis adults that are caught; you will at least have some additional information to make a more informed management decision next spring.

 



Reports of White Grub Injury Still Trickling In
As odd as it seems, we are still receiving an occasional report of white grubs causing damage to crops, although it is not unus

As odd as it seems, we are still receiving an occasional report of white grubs causing damage to crops, although it is not unusual to find grubs in field crops during the summer. Note that the presence of white grubs in a field does not necessarily mean that the grubs are responsible for the injury. So bring your diagnostic skills to bear whenever you visit fields that just don't look right. A mistake in diagnosis could result in unnecessary or misplaced concern.

 



Flights for Second Generations of Corn Borers Are Under Way
Folks in southern counties may be in for a real struggle with southwestern corn borers this year

Folks in southern counties may be in for a real struggle with southwestern corn borers this year. On the other hand, European corn borers continue to be most noticeable by their relative absence. As the next few weeks unfold, we should get a better handle on the potential for infestations of the second generation of both of these pests. Scouting for the second generation of southwestern corn borers should intensify for at least 2 weeks after pollination is complete and should continue throughout July.

This article includes a list of insecticides that are labeled for use against the second generation of southwestern corn borer.



A Reminder About Several Insects in Corn Right Now
This article offers a few comments about several different insects that might be found in cornfields right now

This article offers a few comments about several different insects that might be found in cornfields right now. In addition to the corn rootworms, grape colaspis, southwestern corn borers, and European corn borers discussed in previous articles, you may encounter infestations (although none of them economic) of corn rootworm adults, Japanese beetles, grasshoppers, corn leaf aphids, and woollybear caterpillars. Corn rootworm adults, Japanese beetles, and woollybear caterpillars all clip silks, and grasshoppers and corn leaf aphids can also interfere with pollination and yield potential.

 



Watch for Late-Season Insect Problems
At this point in the growing season, things are progressing well

At this point in the growing season, things are progressing well. Disease and insect problems have been isolated. There may still be some concerns as the season progresses. The first potential problem is grasshoppers. Another is the southwestern corn borer. This article discusses treatments for these insects.



Phytophthora Rot on Soybean
Several reports of Phytophthora root rot on soybeans have been received from around the state

Several reports of Phytophthora root rot on soybeans have been received from around the state. The Phytophthora organism can cause disease symptoms on soybeans at any stage of growth. This article describes the symptoms of the disease.



Update on Fungal Leaf Blights
Common rust is developing in most cornfields around the state

Common rust is developing in most cornfields around the state. Eyespot is showing up on the upper leaves of corn plants in various areas around the state. Remember that what is important about all these leaf blights is not which blight you have but rather the percentage of leaf area blighted as a whole on the plant.



Considerations for Late-Season Soybean Herbicide Applications
Postemergence soybean herbicide applications are still being made to late-planted fields, double-crop soybeans, and fields need

Postemergence soybean herbicide applications are still being made to late-planted fields, double-crop soybeans, and fields needing a "cleanup" due to weed escapes. There are a number of considerations when choosing a postemergence herbicide for that final application.

This article discusses preharvest intervals and rotational crop intervals. Tables are provided that contain information regarding preharvest intervals and grazing restrictions for a number of postemergence soybean herbicides and rotational crop intervals for soybean herbicides.

 



More on Corn and Temperature
Conventional wisdom might say that when the weather is warm and humid, at least it's good weather for corn

Conventional wisdom might say that when the weather is warm and humid, at least it's good weather for corn. Although the belief that weather that's uncomfortably warm and humid is good for corn probably makes us feel a little better when we're having such weather, such conditions really are not ideal for corn growth and yield.

We usually associate humidity with how comfortable it is in the afternoon, but it's often more useful to consider the dewpoint, which is temperature at which the air is saturated. This article discusses the relationship between dewpoint and temperature and how they affect the corn crop.



Regional Reports
Extension center educators, unit educators, and unit assistants in northern, west-central, east-central, and southern Illinois

Extension center educators, unit educators, and unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season.

This week's issue includes reports from east-central Illinois, northern Illinois, southern Illinois, and west-central Illinois.



Preliminary Root-Rating Results for Urbana Corn Rootworm Trial
On July 13, a crew led by John Shaw, Illinois Natural History Survey, dug and washed roots from an experimental corn rootworm trial located just south of Champaign-Urbana. We rated the roots for larval injury and present some of the preliminary results in table form.

Most products performed very well and kept larval injury below a root rating of 3.0 (some light pruning of corn roots) on the Iowa State 1-to-6 injury scale. The level of rootworm "pressure" in the experiment was quite good, with over two nodes of roots destroyed in the untreated control.

On July 24 and 25, we will continue our corn rootworm insecticide efficacy plot evaluations in Monmouth and DeKalb, respectively. As soon as data from these experiments are available, we'll share them with you.

Scouting for Corn Rootworm Adults
Emergence of corn rootworm adults is in "full bloom" throughout Illinois; peak population densities and peak egg laying will occur within the next few weeks. Therefore the time for scouting for rootworm adults is upon us. There are three different reasons for scouting for adult corn rootworms throughout most of state and a fourth reason in the counties in Illinois where western corn rootworms lay eggs in soybeans.

Includes guidelines for scouting for rootworm adults in corn (two different objectives) and soybeans.

Sudden Death Syndrome on Soybean
Sudden death syndrome (SDS) is a disease reported in most of the soybean growing areas of the United States and the world. The soilborne fungus, Fusarium solani f.sp. glycines, which is the causal organism of SDS on soybeans, infects soybean roots. Under severe conditions, SDS can result in flower and pod abortion, premature defoliation, and yield losses. The use of fungicides to control this pathogen has not been effective, and crop rotation does not provide a viable control alternative. Although SDS potentially can be controlled by host-plant resistance and some progress has been made in developing resistant varieties, screening for resistance is difficult because disease expression is often environmentally controlled. Disease surveys conducted around the state have shown that sudden death syndrome occurs more frequently in fields under high production, in wet and compacted areas, and in fields with high populations of soybean cyst nematodes.

Discusses symptoms, current management approaches to take.


Behold White Mold?
Because much of the Illinois soybean crop is in the reproductive phase, it's time to watch for several midseason diseases. Although I have not heard of any reports of white mold in Illinois at this point, should growers in the northern half of the state experience cooler weather along with continued rainfall, white mold may once again rear its ugly head in Illinois.

White mold is favored by moderate temperatures (less than 85°F), normal or excessive rainfall, and high canopy humidity. The first symptoms of white mold generally appear during growth stages R1 through R3 (beginning bloom through beginning pod) and are often aggregated (found in "hot spots") rather than uniform across the field.

Due to the depressed crop price, it is very unlikely that fungicide applications are economical.

Keep Your Eyes Open for Soybean Stem Canker
Stem canker symptoms usually appear in late July or early August, when the pods are starting to fill out, and persist until the crop matures. The fungus is favored by warm temperatures, normal or excessive rainfall, high canopy humidity, and crop damage (for example, due to hail). Discusses symptoms.

Phytophthora root rot has plagued a number of growers this season, and in terms of future variety selection it is important that Phytophthora and stem canker not be confused with each another (see Table 2 for comparison).

Fifty years ago, stem canker was a major problem. However, most varieties available today have good resistance to this disease. If you are experiencing problems with stem canker in certain areas or with certain varieties, consider tillage and rotation to reduce the amount of infested residue, and consider using other varieties that have a good track record against stem canker.

Due to the depressed crop price, it is very unlikely that fungicide applications are economical. There is a checklist on page 110 of the Illinois Agriculture Pest Management Handbook 2000, which will help you determine if a foliar fungicide application should be made to soybean fields.

Regional Reports
Extension Center educators, Unit educators, and Unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season.

This week's issue includes reports from northern Illinois and west-central Illinois.


Entomological Observations from the Road
Earlier this week, our crew evaluated corn rootworm larval injury in our experimental insecticide trials in Monmouth and DeKalb. The remainder of this week will be devoted to washing roots and rating them for larval injury. Root injury was evident at both locations, with the potential for lodging most likely in DeKalb.

As I returned from DeKalb, I was a bit surprised, and disappointed, that more yellow sticky traps were not evident in soybean fields. We recommend that trapping for western corn rootworm adults in soybean fields should begin during the last week of July and continue through the third week in August.


Time to Watch for Defoliators in Soybeans
Although we are not aware of excessive defoliation being caused by any one of the insects discussed in this article (with the possible exception of the Japanese beetle), when soybeans bloom and pods begin to fill out, defoliation by insects can result in noticeable yield loss. Keep in mind that a static threshold may not be appropriate during a year when soybean prices are low. Adjust the percentage defoliation threshold upward to accommodate low prices.

Observations reported of bean leaf beetles, grape colaspis adults, and a few northern corn rootworm adults. Other potential defoliators that may be common in soybean fields in Illinois during this time of year include grasshoppers, green cloverworm, and yellow woollybear caterpillar.

Gives guidelines for scouting a soybean field for evidence of defoliation caused by any of the insects discussed in this article. Although defoliation thresholds accommodate virtually all defoliators, it's important to identify the pests accurately to choose the right insecticide, if warranted. Different insecticides may be labeled for different insects, and the rates of application vary as well.

Gray Leaf Spot of Corn
Gray leaf spot of corn is being reported across the state. Gray leaf spot in a susceptible variety has easily identifiable symptoms: The disease probably would have been more appropriately named tan rectangle blight.

The most severe gray leaf spot epidemics usually occur in continuous-corn-production fields, where there is also a substantial amount of corn debris that was infected in the previous season remaining on the soil surface.

Progress has certainly been made in the past several years in developing hybrids with some level of resistance to the disease. Remember, though, that resistance does not mean the hybrid will not be infected by the disease. Resistance in a resistant hybrid can be expressed in a number of ways: smaller lesions produced, fewer spores subsequently produced from those lesions, a longer time for lesions to develop, or fewer lesions produced overall

Water, Canopy, and the Corn Crop
The main determining factor for yield in most Illinois cornfields will be the water supply for the rest of the season. Although there are few signs that dryness has hurt the crop, there are areas of the state where rainfall during July has been much below normal.

Make no mistake, the crop is in excellent condition in the majority of fields in Illinois. In parts of the state, however, July rainfall has been heavy, and as a result the crop has continued to suffer from lack of root growth and nutrient uptake. Overall, the crop is well positioned for "typical" August weather.

Discusses the measurement called "open pan evaporation," or OPE, and the "crop coefficient," the percentage of OPE that the crop uses; also, assessing the canopy.

Regional Reports
Extension Center educators, Unit educators, and Unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season. This week's issue includes reports from northern and west-central Illinois.


Preliminary Root-Rating Results for DeKalb and Monmouth Corn Rootworm Trials
On July 24 and 25, a crew led by John Shaw, Illinois Natural History Survey, dug and washed roots from experimental corn rootworm trials in Monmouth and DeKalb, respectively. We rated the roots for larval injury and present some of the preliminary results in table form.

Most of the standard soil insecticide products we tested at these locations held up reasonably well to moderate rootworm pressure. Controls (no soil insecticide used) at each location were above a root rating of 4.0 (one node of roots or the equivalent destroyed). Although many of the products performed satisfactorily in our trials, consider that we did not plant corn until mid-May.

As we look back on this summer and examine how products held up to rootworm pressure in producers' fields, it becomes obvious that insecticide performance varied considerably from field to field. Many interacting factors are involved, including planting date, rainfall patterns and amounts, product characteristics, accuracy of application (calibration accuracy), and method of application (band vs. in-furrow). Our results also clearly show that seed treatments did not hold up very well at either location.

Continue Watching for European and Southwestern Corn Borers
The presence of moths indicates that egg laying is ongoing. It is possible that numbers of surviving larvae in some cornfields could be large enough to get our attention. This is especially true for late-planted corn. Even though the price of corn is low, heavy infestations of European corn borers might be worth controlling in fields with high-yield potential.

The southwestern corn borer is a distinctly more critical concern in southern Illinois. The potential for heavy infestations is significant.

Southwestern Corn Borer or Stalk Borer?
I received information of suspected southwestern corn borer larvae in a giant ragweed stem (Clark County) and a cornstalk (Adams County). Fortunately, the individual in Adams County had photographs of the insect, which convinced me that it was a mature stalk borer larva. The distinguishing characteristics of the two pests are the dark stripe on the head of the stalk borer and the large, dark tubercles all over the body of the southwestern corn borer. The people who had found the caterpillar in a giant ragweed stem in Clark County had confirmed that the insect was a mature stalk borer.

Because southwestern corn borers can be very damaging pests, proper identification of spotted caterpillars is very important.

Bean Leaf Beetles Are Easy to Find
In soybean fields and elsewhere, adult bean leaf beetles are fairly common right now. Symptoms of injury are apparent. However, no one has reported significant amounts of defoliation yet.

Of special interest is the possibility that bean leaf beetles might transmit viruses to soybeans. Researchers are investigating the relationships among bean leaf beetles, viruses, and soybean plants; and results of their efforts will be forthcoming this fall.

Sudden Death Syndrome on Soybean
SDS is here and has been reported in several areas of the state where rainfall has been plentiful. SDS also seen in isolated areas where beans were planted early in Adams County, despite recent dry conditions. Discusses symptoms.


Physoderma Brown Spot
Discusses symptoms, causal organism. The presence of this disease should not cause concern. It is not usually economically important.


Corn Diseases
Fungi: The common rust situation on field corn has slowed down somewhat, and currently the only other leaf blight that we have been seeing with any regularity is gray leaf spot.

Viruses:
Some virus symptoms are showing up in the corn in southern Illinois.


Soybean Diseases
Fungi: (Besides SDS;) white mold in irrigated soybeans.

Viruses: Reports of the beginning of virus symptoms in soybean. Most viral diseases in Illinois look very similar in the field. The only way to know for sure is to have them tested; with recommendations.


Regional Reports
Extension Center educators, Unit educators, and Unit assistants in northern, west-central, east-central, and southern Illinois prepare regional reports to provide more localized insight into pest situations and crop conditions in Illinois. The reports will keep you up to date on situations in field and forage crops as they develop throughout the season. This week's issue includes reports from northern and west-central Illinois.


Corn Rootworm Larval Injury Evaluated in First-Year Cornfields
In late July, Susan Ratcliffe, Extension entomologist, coordinated a large root-retrieval project. We extend our thanks to all those who participated. Ultimately, we hope to refine our economic threshold even more when these data (presented here in table form) are further evaluated.

A cursory examination of these preliminary data reveals considerable variation in root injury from field to field. These data show that only 13 of 36 fields exceeded the economic injury index of 3.0 in untreated check strips.

Keep Your Eye on European Corn Borers
As a follow up to last week's story, note that Alan Mosler with Twin Counties FS indicated on August 4 that second and third instars were present throughout southern counties and that boring into stalks was imminent.

For the rest of the state, it's worth noting that European corn borer adults are rather common. I have also heard of small pockets of significant infestations in several areas of the state.


Blister Beetles in Corn, As Well As Alfalfa and Soybeans
Dennis Epplin, crop systems educator in Mt. Vernon, recently reported blister beetles stripping some corn plants, including the silks, in a cornfield in Jefferson County. He had been finding intense, localized infestations of blister beetles in alfalfa and soybeans earlier this summer, but the infestation he encountered in corn was the most severe. Although the infestation was not economic (from a whole-field perspective), the injury was devastating in small areas of the field.

Description of the beetle provided and pictures in the Web version.

We consider blister beetles to be more beneficial than pestiferous (although their presence in alfalfa hay is a notable exception). Therefore, it's best not to overreact to their presence, even though injury to the plants can be quite severe in areas of the field where the beetles congregate.



The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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