A systematic, diverse approach to corn rootworm management is needed if growers are to have successful corn-on-corn acres in the future, said Dr. Aaron Gassmann while presenting last month during the 25^th Annual Integrated Crop Management Conference on the Iowa State University campus.

Since 2009, Dr. Gassmann has studied the use of Bt corn hybrids in Iowa.  He says the number of fields showing severe rootworm injury has increased every year primarily due to the overuse of one specific trait on fields for many consecutive years, lack of refuge compliance, and lack of scouting for both larval rootworm and adult beetles.

Farms with continuous corn production, and specifically those fields planted to the same Bt event year-after-year, are most at-risk for developing a resistant population. To delay resistance, Dr. Gassman and his colleagues recommend the following IPM approaches:

• Rotate to soybeans or other crops to break the corn rootworm life cycle between growing seasons.
• Consider using corn that contains different Bt proteins than ones that may have performed poorly in the past.
• Consider using pyramided Bt hybrids, which is defined as corn that contains multiple Bt proteins targeting corn rootworm.

Implementing a long-term integrated approach to corn rootworm management is most important, according to Gassmann. Integration of tactics across seasons is fundamental to prolonging the usefulness of any effective management strategy

Two months ago I posted a blog, encouraging farmers to scout every field for rootworm.  Because of the wide variance in planting dates in 2013, it’s important to continually inspect every field – regardless of seed selection – for insect pressure.

With adult corn rootworm becoming active during silking this year, we highly recommend keeping an eye on fields in order to protect yield.  Now it is a good time to assess corn rootworm activity: score injury caused by larvae, and monitor adult activity in corn.  Late-planted fields or late-flowering hybrids are generally attractive to adult corn rootworm beetles.  Silks will still be developing in these fields when older fields have brown or drying silks.  Adults may migrate and aggregate in this later-maturing fields.

Also evaluate root injury to better understand the efficacy of your management program.  Monitoring over several years will help establish a historical record of how larvae respond to management tactics (e.g., crop rotation, Bt corn, soil insecticides, etc.). One common outcome of severe larval feeding is lodging of corn plants.  However, it is important to confirm that feeding from corn rootworm was the cause of lodging and that it did not results from other factors such as strong winds.

To help assess injury, ISU Entomologist Aaron J. Gassmann developed an Interactive Node Injury Scale.  Injury assessment made now and field notes taken will help you select seed products for 2014.  To prevent corn rootworm damage from reaching devastating levels, plant a portfolio of products.

Continued use of the same rootworm-resistant trait in corn hybrids, an increase of corn-on-corn areas, plus a lack of refuge acres, has caused rootworm resistance to become an issue in some areas.  Best management practices to reduce corn rootworm pressure in the future include: crop rotation, trait rotation and respecting the refuge.

Respecting the refuge just got easier thanks to the EPA last week granting approval of Agrisure Duracade E-Z Refuge trait stacks.  New, for 2014 planting, Latham® Hi‑Tech Hybrids is offering Agrisure Duracade^TM as another option in the fight against corn rootworm.  

Farmers have a chance to see Latham’s new 2014 products this Saturday, Aug. 24, when we host the 5^th Annual Latham Freedom of Independence Ride.  This year’s ride begins and ends in Lewis & Clark State Park in Onawa.  It’s free and open to motorcycles, classic cars and even pickup trucks.  For more details, visit our company website lathamseeds.com.  Then click on the Freedom Ride icon.  Pre-register today, and we’ll see you Saturday on the open road!