COLUMNISTS

Controlling corn rootworm begins now

Josh Kamps
These western corn rootworm adult beetles emerge late June through
August and lay eggs almost exclusively in corn fields from early August through
early September.

The Dog Days of Summer begin July 3rd and last through August 11th. This time frame for farmers is normally associated with ideal corn growing weather and a slight break from the long hours of spring planting and fall harvest. 

Perhaps a few days will be spent at the county fair, projects long overdue from the “to do” list will rise to the top or a family vacation will be scheduled. With many pest management decisions already completed for this season, it is however an opportune time to begin crop scouting corn acres for 2022 corn rootworm pressure.

Effective pest management requires identifying the pest, understanding the life cycle and timeline of development and measuring the size of the population. 

Field crop scouting for corn rootworm pressure begins about 9 months ahead of corn planting during the adult beetle egg-laying period, mid-July through August. Adult corn rootworm beetles begin to emerge in late June following completion of the larval growth stage below the soil surface. 

The corn plant is the sole food source for corn rootworm larvae (roots) and corn rootworm adults (silk and pollen). By early August, corn rootworm adults begin laying eggs in the soil to over-winter and hatch in early June 2022. 

Few field crop pests divulge their crop damage plans for the upcoming growing season like corn rootworm. The crop damage plan for the following season is understood by field scouting for adult corn rootworm beetles and studying corn root injury level.

Field Scouting for Corn Rootworm is a resource available through the UW-Madison IPM program. This information is useful for making pest management decisions well in advance of the 2022 growing season. 

As mentioned, corn rootworm will not survive past egg hatch without available living corn roots to feed on. Concentrate scouting efforts on fields planned for corn-on-corn production. By understanding the current level of corn rootworm pressure, developing a specific management plan increases the level of control and reduce the risk of resistant populations developing. 

Successfully controlling corn rootworm below the economic threshold begins well in advance of the current growing season. Discuss a management plan now with a trusted agronomist or crop advisor.

Include field crop scouting of root injury and adult beetle counts as the foundation for rating the current pest management system. Then review the available tools in the pest management toolbox. 

The toolbox contains: crop rotation, Bt corn rootworm hybrids and soil applied insecticide, foliar insecticide and neonicotinoid seed treatment as potential control tools. Corn rootworm has adapted to control practices in the past and should be considered capable to adapt to control practices in the future. 

Corn rootworm adaptation

Examples of corn rootworm adaption to survive include: location of egg laying, extended diapause and genetic Bt protein resistance. 

If a pest management tool becomes overwhelmed, rotating to a new tool is the preferred decision rather than layering multiple pest management tools together.

The rationale for rotating tools compared to layering tools is to extend the length of time the current pest management tools are effective on local corn rootworm populations. In addition, the risk of pest resistance to control tools reduces when used in rotation instead of frequently used in a layered approach. 

Corn Rootworms in Wisconsin: A Brief Overview of Bt Resistance and Management is a resource available through the Extension Crops and Soils Program.      

Enjoy the 2021 Dog Days of Summer by attending a social outing, completing a long overdue project or spending time with family and friends. Also, consider scheduling time to scout corn fields for corn rootworm activity and pressure. 

The time spent field crop scouting now will help with managing corn rootworm pressure in 2022 and beyond.

For additional information regarding corn rootworm management, visit the UW-Madison Division of Extension Crops and Soils program, UW-Madison IPM program or contact your local county Extension office.

Josh Kamps

Josh Kamps is the Agricultural Educator for UW Extension-Lafayette County

UW-Extension