Managing western corn rootworm with Bt corn

decrease font size  Resize text   increase font size       Printer-friendly version of this article Printer-friendly version of this article

During the summer of 2011, the ISU Corn Entomology Lab visited several fields in Iowa in response to complaints for rootworm injury to Bt rootworm corn, and to follow-up on fields that were visited in 2010 in response to grower complaints. To date, resistance of western corn rootworm has been found only for Bt corn producing Cry3Bb1, which was originally released as YieldGard Rootworm and is now the rootworm trait found in VTTriple and VTTriple Pro. Cry3Bb1 also is present as a pyramid with Bt toxin Cry35/35Ab1 in SmartStax. 

click image to zoom Field visits in 2011 found some fields with severe root injury to Cry3Bb1 corn and to corn that produces Bt protein mCry3a, which is the Bt trait found in Agrisure (a Syngenta Product) and TRIsect (a Pioneer Product). We currently do not know the reason for the high level of rootworm injury observed for mCry3a rootworm corn, but this is an active area of research in the Gassmann Laboratory. So far in 2012, we have visited several fields with heavy rootworm feeding injury to Bt corn and patterns of injury are similar to 2011. 

Data from field visits in 2011 and 2012 suggest that caution should be used when managing rootworm in continuous corn with either Cry3Bb1 traits or mCry3a traits. It is important to check continuous cornfields for rootworm injury. A high abundance of adult corn rootworm in a field is an indication of potential problems with larval management, but only digging and evaluating corn roots can confirm the presence of larval feeding injury. The relationship between root injury and yield is complicated and depends on several factors, such as soil moisture. A reasonable economic threshold for larval rootworm injury is 0.25 nodes, which means that ensuring less than 0.25 nodes of injury on average is an economically sound management practice, but achieving further reductions in injury is not warranted.    

click image to zoomFigure 1. A cornfield visited in Iowa during 2012 that was planted to Bt corn. The planting pattern in the photographed area alternated between 12 rows of Cry3Bb1 corn and 12 rows of mCry3a corn. As growers think about seed selection for 2013, they should be aware of current challenges encountered when managing corn rootworm with Bt corn, and use integrated pest management (IPM). Crop rotation, for example rotation to soybeans, is a highly effective way to manage western corn rootworm in Iowa. If farmers are concerned about extended diapause in northern corn rootworm, they can consider protecting first year corn with a soil-applied insecticide or Bt corn. In addition to crop rotation, growers should alternate their management tactics to control corn rootworm if they are growing continuous corn. Current options include rotation among single trait events, pyramided Bt events (corn that contains multiple traits targeting corn rootworm) and non-Bt corn with a soil-applied insecticide.  


Buyers Guide

Doyle Equipment Manufacturing Co.
Doyle Equipment Manufacturing prides themselves as being “The King of the Rotary’s” with their Direct Drive Rotary Blend Systems. With numerous setup possibilities and sizes, ranging from a  more...
A.J. Sackett Sons & Company
Sackett Blend Towers feature the H.I.M, High Intensity Mixer, the next generation of blending and coating technology which supports Precision Fertilizer Blending®. Its unique design allows  more...
R&R Manufacturing Inc.
The R&R Minuteman Blend System is the original proven performer. Fast, precise blending with a compact foot print. Significantly lower horsepower requirement. Low inload height with large  more...
Junge Control Inc.
Junge Control Inc. creates state-of-the-art product blending and measuring solutions that allow you to totally maximize operating efficiency with amazing accuracy and repeatability, superior  more...
Yargus Manufacturing
The flagship blending system for the Layco product line is the fully automated Layco DW System™. The advanced technology of the Layco DW (Declining Weight) system results in a blending  more...
Yargus Manufacturing
The LAYCOTE™ Automated Coating System provides a new level of coating accuracy for a stand-alone coating system or for coating (impregnating) in an automated blending system. The unique  more...
John Deere
The DN345 Drawn Dry Spreader can carry more than 12 tons of fertilizer and 17.5 tons of lime. Designed to operate at field speeds up to 20 MPH with full loads and the G4 spreader uniformly  more...
Force Unlimited
The Pro-Force is a multi-purpose spreader with a wider apron and steeper sides. Our Pro-Force has the most aggressive 30” spinner on the market, and is capable of spreading higher rates of  more...
BBI Spreaders
MagnaSpread 2 & MagnaSpread 3 — With BBI’s patented multi-bin technology, these spreaders operate multiple hoppers guided by independent, variable-rate technology. These models are built on  more...


Comments (0) Leave a comment 

Name
e-Mail (required)
Location

Comment:

characters left


LAYCOTE™ Automated Coating System

The New LAYCOTE™ Automated Coating System provides coating accuracy for stand-alone coating systems and for coatings (impregnating) in automated blending ... Read More

View all Products in this segment

View All Buyers Guides

Feedback Form
Feedback Form