EZ Insights with Jon & Corey

Corn rootworms haven't been as much of a "pest" the last few years in MN with plenty of rainfall in the spring that helped reduce their survivability, plus timely late-season rains that aided in root regeneration and growth,  masking much of the insect pressure that may have been present. 2020 is a different story, with significant corn rootworm beetles (CRW) found across the countryside, especially in corn-on-corn situations. 

Now is the time to start determining CRW levels to help in decision making for 2021! Check the video out below for things to watch for!

Corn Rootworm Lifecycle
The main concern with rootworm feeding is the damage they do to the root system. First-instar larvae feed on root hairs and the outer root tissue, while second instars feed on more lateral roots, and sometimes burrow deeper into the roots. The mature 3^rd instars wreak the most havoc by burrowing into the roots and making tunnels lengthwise up through the central portion of the nodal and brace roots. The damage severely limits the amount of water and nutrients that the plant can take up, and limits the stability that the brace roots can offer.

By now, most larvae have finished feeding on roots and have  transformed into adult beetles. Once they emerge from the soil, they can feed on leaves and silks. If corn is still in the pollination process, they can wreak havoc when the clip silks. 

Monitoring the Level of Pressure
The level of corn rootworm beetles (CRW) present in the field this year will be critical to know to determine the course of action for next year. Deciding if the acres can be corn-on-corn, the need for planting corn with below-ground traits for protection, adding an in-furrow insecticide, or even switching to a non-host crop, monitoring the number of CRW beetle's that can lay eggs will help make a more informed decision.

Yellow sticky traps can be used to get a baseline of the amount of beetle's in the field. Sticky traps should be set at corn silking and continue through the dent stage to monitor levels. 

Economic threshold's of CRW beetles differ some based on the state, but Extension entomologists at the University of Illinois and Iowa State University have outlined the following actions thresholds in beetles/trap/day to provide the economic damage potential for the following season:

• Less than 2 beetles/trap/day indicate a relatively low risk of economic damage.
  • Greater than 1 beetle/trap/day suggests a low risk for economic damage but could indicate populations are increasing.
• Greater than 2 beetles/trap/day indicate the probability for economic damage is likely if control measures are not used. 
• Greater than 5 beetles indicate that economic damage is very likely and populations are expected to be very high the following year.

As you start making decisions for next year, consider some of the data and insights found in the link below around corn trait needs and differences!