Pest & Crop

Purdue Cooperative Extension Service
September 2, 2005

Pest & Crop Newsletter, Entomology Extension, Purdue University

In This Issue Insects, Mites, and Nematodes

Inspect Seed Production Soybean for Bean Leaf Beetle Pod Feeding - (John Obermeyer, Christian Krupke, and Larry Bledsoe)

  • Inspect for bean leaf beetle feeding on pods.
  • Pod damage may result in poor seed quality.
  • Green pods are more attractive than yellow ones.
  • Management threshold depends on several factors.
Bean leaf beetle feeding on pods

Bean leaf beetle feeding on pods.

While sweeping soybean fields for western corn rootworm beetles over the past several weeks, we saw varying numbers of bean leaf beetles. Overall the bean leaf beetle numbers are low and of little concern to commercial production fields. Soybeans grown for seed should be monitored as leaves begin to yellow and pods remain green. Bean leaf beetles scar the surface of pods, but only occasionally feed through the pod to the developing beans. During pod maturation, this scar often cracks leaving an entry hole for air borne plant pathogens that may cause discolored, moldy, shriveled, and/or diseased beans.

Bean leaf beetle pod scarring

Bean leaf beetle pod scarring.



It is important for pest managers to be able to predict whether economic damage will occur based on the types and numbers of beetles that are present and the stage of pod development (i.e., green, yellow, yellow-brown, or brown pods). Once the pods turn yellow to yellow-brown, they become less attractive and less susceptible to damage. Control is normally not warranted from this point on (see the following table).

Randomly select 2 plants in each of 5 areas of the field and count the number of pods per plant and the number that show damage (10 total plants). Figure the percentage of damaged pods per plant for the field as a whole. Note if the pods are green, beginning to turn yellow, or are yellow/brown. Also determine the number of beetles per sweep using an insect sweep net. Take 5 sets of 20 sweeps in the field. Determine the number of bean leaf beetles per sweep. Additionally, note whether beetles are still actively feeding while surveying the field.

Pod Injury Level
No. of Beetles Per Sweep in 30 Inch (7 Inch) Row Spacing
Less Than 4(3)
4(3) to 7(5)
More than 7(5)
0 to 8%
Discontinue Sampling
Sample again in 5 days
Control (preventive) if pods still green
8 to 12%
Sample again in 5 days
Control if pods are still green
Control if pods are green to yellow
Over 12%
Control if pods are still green and beetles are present
Control unless pods are completely dry
Control unless pods are completely dry
Table modified from the University of Illinois.

There has been considerable interest in bean leaf beetle and its association with bean pod mottle virus. Bean leaf beetle is one of major beetle-vectors of this disease. They spread the virus by feeding on infected plants, ingesting the virus with plant tissue, and then regurgitating gut content after moving to and feeding on an uninfected plant. Bean pod mottle virus symptoms at harvest include green stem and hilum bleeding. Treatment for bean leaf beetle to reduce bean pod mottle virus this time of the year is not recommended, as most disease transmission occurs early in the season.

Use the table to the right to determine when a treatment may be necessary.

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No Reports of Hessian Fly Damage in 2005 – (Sue Cambron)

  • Planting after the fly-free date is a key management strategy for reducing Hessian fly problems.
  • Destruction of volunteer wheat helps reduce insect reservoir to avoid spring infestations.

The Hessian fly is present in wheat-growing areas throughout Indiana and often survives, although in lower numbers, in wheat stubble or grasses during the summer. No fly damage was reported in Indiana in 2005, however there is potential for rapid increase of fly populations as a result of weather conditions or cropping practices that favor survival of eggs and young larvae in the fall.

Much of the fall fly population can be avoided by planting after the fly-free date. This is key to avoiding subsequent infestation by the spring brood. Additionally, it has been shown that following the fly-free date will help reduce wheat disease problems and reduce winter-kill from excessive growth. Crop rotation, where wheat following wheat is avoided, also is one of the key management strategies for reducing Hessian fly problems.

The Hessian fly passes the summer in the stubble of the current wheat crop. Plowing the stubble results in the destruction of the pest. Volunteer wheat germinates and begins growing just in time for the fall emergence of the Hessian fly.  These plants are readily infested resulting in a rapid build-up of the population. Removal of volunteer wheat before the emergence of the fall brood greatly reduces the insect reservoir for a spring infestation.

If weather conditions this fall are mild there could still be an infestation of flies that survive on surrounding grasses, so following the fly-free dates for planting is always recommended.

"Fly-Free" Dates For Seeding Wheat

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Click for Table.
Black Light Catch Report

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Weeds to Look Out For – (Bill Johnson and Glenn Nice)

As we move into the latter part of the growing season, we wanted to take this opportunity to discuss a few perennial weed management issues pertinent to the 2005 growing season.  As the crops mature and we begin to run the combines through the fields, we will have the opportunity to assess the effectiveness of this years weed management programs and plan fall activities to manage perennials.

Dandelion.  Spring and in-season dandelion control in the northern and eastern parts of Indiana was a challenge in 2005.  This was due primarily to the fact that 1) dandelion is tougher to control in the spring than in the fall and 2) we experienced dry weather in the early part of the spring and herbicide applications made in May and June were challenged by lack of adequate soil moisture and drought stressed plants.  In several instances we observed severe stand loss in corn due to heavy dandelion infestations. The most effective treatments for reduce infestations of dandelion includes the use of fall treatments. Here are a few treatments to consider for fields with heavy dandelion infestations.  If it is undecided on whether corn or soybean will be grown in a field, use 2,4-D (1 qt/A of 4 lb ai/gallon formulations) + glyphosate (0.38 to 0.56 lb ae/A).  For fields going to soybean, Canopy EX or Synchrony + Express + 2.4-D or glyphosate has been very effective in our research plots.  For fields going to corn, Simazine + 2,4-D or Basis + 2,4-D has also worked well in our plots.  Apply all treatments when dandelion are at least 4 inches in diameter and after a light frost for best results.  The optimal timing will likely occur sometime between mid October and mid November.  There are a number of spring treatments that can provide good activity, but in general, we have had very consistent success with the fall treatments listed above on controlling dandelion.

Pokeweed. Pokeweed really appeared to take off in 2005 and was evident in more fields than I can remember in the recent past.  As in 2004, we observed a large number of fields where the pokeweed really took off in early June and reach 3 to 5 feet tall before it was sprayed.  Although, we now observe a lot of dead above ground tissue, keep in mind that this weed is a perennial, the root balls can be very large, and effective, long-term control with 1 herbicide application is unlikely.  As you walk or combine soybean and corn fields, look for new pokeweed sprouts from the base of “dead” plants, particularly in areas where soybean canopy development is poor.  After combining, if live actively growing leaf tissue is present and effective spray coverage can be achieved, consider a fall treatment of glyphosate (1.1 to 1.5 lb ae/A) + 2,4-D (0.5 to 0.75 lb ai/A) or dicamba in late September or early October, but before a frost.  Since pokeweed is an erect herbaceous perennial, the above ground tissue will be damaged or killed by frost.   

For fields that have both pokeweed and dandelion, the optimal herbicide timing will likely be prior to a frost. Treatments after a frost may not be effective on pokeweed, but will likely be effective on dandelion. Tree species such as sugar maples and cedars are occasionally problematic in our no-till systems. For fields that have both pokeweed and tree species such as maples, consider using dicamba + glyphosate rather than 2,4-D + glyphosate.  Dicamba will be more effective on tree species than 2,4-D.  These applications should be made before frost as well.  A key consideration for maple control will be the ability to make applications when live leaf tissue is present.  If tree leaf tissue is not present, the best option may be to aggressively till the areas where the trees are present.  Typically the maple tree infestations are patches on the downwind side of established maple trees growing in years or along field edges.

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Agronomy Tips

Take Time Now to Evaluate Hybrid Plots - (Bob Nielsen)

Even though the 2006 growing season is almost eight months away, growers are feeling the urge and, more importantly, the sales pressure to consider their hybrid purchasing decisions now. Obviously, the major objective of hybrid selection by growers should be to identify hybrids with consistent yield performance. The term “consistent performance” simply refers to a hybrid’s ability to yield well across a range of growing conditions.

Identifying consistent hybrid performers requires comparative yield data from a number of locations and, ideally, across several years. Growers should routinely ask for and study such widespread yield performance data from their seed dealers as well as from other public sources of yield data (universities, county Extension plots, and other local trials) before selecting hybrids for next year.

In addition to yield data, growers should take advantage of the opportunities now to walk seed company or on-farm variety trials and evaluate other hybrid characteristics that may be of importance to their purchasing decisions. It seems like you see signed on-farm variety trials every other mile as you drive through the countryside this time of year. Seed corn company field days seem to be happening everywhere you look these last days of August and into early September and every one will highlight their lineup of hybrids with signed plots.

Just don’t walk along the front of these plots, but take the time to walk into the plots and carefully evaluate hybrid characteristics like plant & ear height, late-season leaf & stalk health, standability, relative maturity, brace root development, husk coverage of the ear, and ear size. Just don’t make mental notes, but rather take the effort to record the hybrid numbers and your observations about each. Such information plus that available from seed company literature plus comparative yield performance data will help growers make more informed hybrid purchasing decisions.

Remember that successful corn growers understand the difference between purchasing crop production inputs versus being sold crop production inputs.

Related References

Farmers’ Independent Research of Seed Technologies. 2005. Results of independent on-farm variety trials. Available online at [URL verified 8/29/05].

Purdue Cooperative Extension Service. 2005. Results of county-based variety performance trials for Warrick, Gibson, Posey, and Spencer Counties, Indiana.. Available online at [URL verified 8/29/05].

Purdue Cooperative Extension Service. 2005. Results of county-based variety performance trials for Adams County, Indiana.. Available online at [URL verified 8/29/05].

Purdue Crop Performance Program. 2005. Results of statewide crop variety performance trials located throughout Indiana. Purdue University. Available online at [URL verified 8/29/05].

Thomison, Peter. 1995. Key Steps in Corn Hybrid Selection. Ohio State Univ. Cooperative Extension Service publication no. AGF-125-95. Available online at [URL verified 8/29/05].

Thomison, Peter. 1995. Tips for Evaluating Corn Hybrid Test Plots. Ohio State Univ. Cooperative Extension Service publication no. AGF-123-95. Available online at [URL verified 8/29/05].

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Top Leaf Death in Corn - (Bob Nielsen)

If you have been watching corn or popcorn fields lately as you drive through the countryside, you may have noticed what seems like an unusual pattern of leaf senescence (the natural age-related deterioration and ultimately death of plant tissue) as this year’s crop nears the end of the season. Leaves in these fields are dying from both the top and the bottom of the plants, with green leaves remaining in the middle. In some fields, the death of the upper leaves prior to lower ones is very striking and gives the fields an unusual golden “glow” against the morning or evening sun.

Some of the guys down at the Chat ‘n Chew Café say they remember that corn usually “dies” or “matures” beginning at the bottom of the plant and moving to the top, not both ends progressing toward the middle. What gives?

Death of top leaves may occur from one or more of several factors and may be partially distinguished by whether all plants are affected or only random plants throughout a field. The ultimate effect on grain yield obviously depends on how early in the grain-filling period the death of the upper leaves occurs.

Top Leaf Death in Random Plant

Related References

Bessin, Ric. 2004. Southwestern Corn Borer. Univ. of Kentucky Extension. Available online at [URL verified 8/28/05].

Lipps, Patrick and Dennis Mills. 2001. Anthracnose Leaf Blight and Stalk Rot of Corn. Ohio State Univ. Extension Pub. AC-0022-01. Available online at [URL verified 8/28/05].

Munkvold, Gary. 2002. Anthracnose top dieback is back. Integrated Crop Management Newsletter. Iowa State Univ. Available online at [URL verified 8/26/05].

Tollenaar, Matthijs & Terry Daynard. 1978. Leaf Senescence in Short-Season Maize Hybrids. Can. J. Plant Sci. 58: 869-874.

Valentinuz, Oscar R. and Matthijs Tollenaar. 2004. Vertical Profile of Leaf Senescence during the Grain-Filling Period in Older and Newer Maize Hybrids. Crop Sci. 44:827-834.

VanDyk, John. 2005. European Corn Borer Home Page. Iowa State Univ. Available online at [URL verified 8/28/05].

For other Corny News Network articles, browse through the CNN Archives at

For other information about corn, take a look at the Corn Growers’ Guidebook at

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Weather Update
Temperatures as of August 31, 2005

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