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5/16/2011 - 5/22/2011

Corn Flea Beetles are Active in Corn

Erin Hodgson, Department of Entomology

Chad Patterson, Webster City area, recently reported finding corn flea beetles feeding on seedling corn in central Iowa. Corn flea beetles are small, shiny and black (Fig. 1), and about 1/16 inch long. The adults feed by scraping parallel to the veins along upper or lower leaf surfaces. The scratches create a “windowpane” effect where the tissue looks bleached or silvery (Fig. 2). Sometimes the feeding scars resemble foliar diseases such as gray leaf spot or Northern corn leaf blight.

The feeding rarely causes economic damage to established corn, but can sometimes kill corn seedlings with high beetle populations. Growers should be aware that corn leaf beetle can vector a bacterium called Pantoea stewartii (Erwinia stewartii), that causes Stewart’s wilt bacterial disease. Susceptible varieties of sweet corn hybrids and seed corn inbreds may be infected during the seedling stage but not show any symptoms until later in the summer. Infected plants will be covered in leaf lesions, not produce an ear, or die. 
 

Figure 1. Corn flea beetles are shiny black with enlarged hind legs for jumping. Photo credit Mike Quinn, www.bugguide.net.

 


Figure 2. Heavy infestations of corn flea beetle can leave feeding scars that look like disease lesions. Photo credit University of Illinois-Urbana archives, www.ipmimages.org.


In an ICM News article earlier this year, Forrest Nutter made predictions about Stewart’s wilt disease in Iowa. He summarized the statewide risk level as “negligible to low” based on the Stevens-Boewe Index and Iowa State Stewart’s disease model. Although the predicted risk is low, scouting for corn flea beetle as corn emerges is recommended. Special attention to scouting and feeding damage should be made for seed corn and susceptible varieties. Adults move into fields from grassy overwintering areas, and infestations typically start at field edges. Begin looking at 20 plants at five locations in each field and determine the number of adults per plant. Use the following thresholds for rescue treatments in corn:

  • Field corn - prior to stage V5, 50 percent of plants with severe feeding injury and five or more beetles per plant.
  • Seed corn - on susceptible inbreds, 10 percent of the plants with severe feeding injury and two or more beetles per plant.

Management options

Currently labeled products include pyrethroids (Asana XL, Mustang Max, Warrior II), organophosphates (Lorsban 4E, Nufos 4E), and carbamates (Lannate LV, Sevin 4F). See manufacturer's labels for use rates and restrictions. Corn flea beetle management considerations include seed selection and cultural practices. Incorporating host plant resistant hybrids will help prevent feeding and disease transmission. Systemic seed treatments provide early season control of corn flea beetle and Stewart’s wilt in corn. Keep fields and surrounding areas weed-free to minimize overwintering habitat and food sources for larvae and adults. For susceptible varieties, plant later to avoid the spring migration of adults.

 

Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847.

You Can ‘Row’ the Corn

By Roger Elmore, Department of Agronomy

Ninety-two percent of Iowa’s 2011 corn acreage was planted as of May 15, according to the USDA-NASS report. Our planting progress finally pushed above the five year average and approached the progress on the same date last year. A third of Iowa’s corn had emerged at the time of the report. Since then, we’ve had a few good planting days and some warmer temperatures and sunshine. The next USDA-NASS report will likely show nearly all of our corn planted and most of it emerged. 

Growing up with corn and throughout my career I’ve heard, and said, “You can row the corn!” This has nothing to do with braiding hair. Here’s the way I understand the use of those words:

Rowing corn - A definition: The ability to observe rows of freshly emerged corn from the end of the field or as you drive by at 25, or even 55, miles per hour. It is a remote measure of crop growth. 

Perhaps it’s a big deal because it denotes a milestone for the crop and marks, hopefully, the end of the planting season at least for that specific field. Certainly it tells us there are enough plants emerged together to display long lines of green converging on the horizon. An amazing sight. No pun intended!

row the corn

Figure 1.  You can ‘row‘ the corn, Story County, IA; 19 May 2011.


Time to walk fields

But, don’t let the beauty of the long straight rows of freshly emerged corn lull you into contentment. This is the time to walk your fields. If something catches your eye or looks amiss, put on your CSI (crime scene investigation) hat and check it out. Count the emerged plants. Look for ‘wild’ variability in plant to plant spacing – small differences are less important than achieving proper plant populations. (See the articles on Planter Speed and Uniformity on the Planting tab on the Iowa State University agronomy corn production Web page). Look for variation in plant emergence and size. Uniform plant emergence and plant population are far more important than plant spacing in most fields. 

Dig slow-to-emerge plants or kernels in skips and compare them to earlier-emerged, neighboring plants. Ask why are they different? The answer may surprise you. Check planting depth, sidewall compaction, surface compaction, residue proximity, surface crusting, germination failure, insect feeding, mesocotyl rot, weed competition; and the list can go on and on.  (See the articles on Crop Establishment and Appearance on the Early Season tab on the ISU agronomy corn production page). Perhaps the planter speed was too fast, the seed bed too wet, etc.?

Figures 2 and 3 show a row segment with four plants at different stages ranging from germinating, to VE, to V1. It takes 90 to 120 growing degree day units (GDD) from planting to emergence and another 84 GDD for every new leaf from VE to V10. With this in mind, there is about 150 GDD difference between the first plants to emerge – positions 1 and 4 - and the seed in position 2 which is just sprouting. As of week ending May 20, although normal GDD accumulation is about 13 per day, we’ve only accumulated about seven per day in the last week.

This slow heat unit accumulation will handicap un-emerged plants relative to those that emerged earlier and set up lower yield potential on the late emerging plants. Seed depth and/or surface residue of the two later seeds/plants - positions 2 and 3 in Figure 3 - may have differed from that of plants 1 and 4 and slowed their emergence. Fortunately there were less than 5 percent un-emerged plants in this Story County field.

The conclusions you reach during your CSI investigation may not help you now or for that matter anytime this growing season. But it will help you next year. Plan ahead!

Now is the time to walk your fields!

Figure 2. Top view of a short segment of corn row with three emerged plants (positions 1, 3 (barely emerged), and 4 (emerged) and one not yet emerged (position 2). Story County, Iowa; 19 May 2011.

Figure 3. Seeds and plants from positions 2, 3, and 4 from Figure 2.

 

 

Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at relmore@iastate.edu or (515) 294-6655.

Crop Minute - In the Corn Field

 Roger Elmore, ISU Extension corn specialist, discusses yellow corn emergence and the benefits to producers who walk their fields gathering information to prepare for next year. Look for the weekly Crop Minute on the right side of the ICM News homepage, under More Resources. Or go directly to the May 16, 2011 interviews (mp3).



This article was published originally on 5/23/2011 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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