Agronomy Blog

Corn Rootworm Mangement or Not?

by Travis Dollarhide | Feb 23, 2018

One of the toughest decisions for farmers in the traditional high corn root worm pressure geography is the choices to be made for controlling corn rootworms. Two main factors are coming to play in this decision, first low market prices for corn and secondly several years of lower rootworm pressure, especially in the eastern Corn Belt. Economic pressures have farmers considering trait packages with no additional rootworm control and some with soil applied insecticide only. Many factors can influence the severity of rootworm pressure and the damage done even when the pressure is high. The facts are none of this is very predictable when a cropping plan is being developed or even at planting except in the case of continuous corn. The point of this article is to review the distribution of corn rootworms, look at the last two years sampling data and to think about the options for control. There is one good chance to control rootworms except in the case of some chemigation systems and that is at planting.

Here’s the big picture
Map of root worm area including soybean variant and northern diapause:
Travis Rootworm 1 cited

Controlling corn rootworms has involved these methods

  • Rotation to a non-host crop – This can be anything that is not a grass species. Soybeans are the most common example. The problem with this is the wide distribution of two different populations of the pest that have developed ways to very effectively overcome the crop rotation option.
    • The soybean variant of the western corn rootworm where a high percentage of the beetles lay their eggs in nearby soybean fields where they hatch when corn is planted there the following year.
    • The Diapause variant of the northern corn rootworm where a sizable portion of the eggs do not hatch until the second year after being laid
  • Soil applied Insecticides – Can very effectively control rootworms and many have additional benefits in controlling other below ground pests including grubs and wireworms. Insecticides do have their drawbacks which is why the rootworm protection traits were so quickly adopted by the farming community.
    • Expensive equipment to apply the product adding weight to the planter and creating another step in the planting process
    • Metering accuracy especially with higher speed planters
    • Weather variables -too wet can mean loss before the rootworms hatch and too dry can interfere with activation
    • Length of time the product is effective in controlling rootworms, normal ½ life of the product is about 45 days which means early planting dates relative to rootworm hatch can be at risk
    • Handling hazard – Insecticides have the unfortunate effect of being dangerous to humans also
    • All soil applied insecticides are not created equal and the good ones are expensive
  • Rootworm protection traits- Very effective and are almost always paired with a neonicotinoid seed treatment insecticide for secondary pest control.
    • Probably the main objection is the traits are, as we like to say in the seed business “priced to value”
    • Another concern is, are they effective? The bad rap in this is the single mode of action products which in many areas lost effectiveness because the rootworms were quickly developing resistance to them. The EPA has mandated that 2018 is the last year these can be sold and thereafter all rootworm traits must have multiple modes of action. Products like Genuity Smartstax have multiple modes and are widely available and have been for number of years.
    • Reports of failure even in multiple modes of action products. In very high rootworm pressure situations, usually continuous corn in high organic matter soils, it has happened. To dig deeper into this, remember the rootworm must feed on the roots of the plant to ingest the protein that causes it to sicken and die. Very large numbers of rootworms can eat enough to cause economic injury to the plants
    • Advantages over soil applied insecticides
      • Traits are not affected by weather, metering, require no extra equipment, and have no handling requirements other than standard seed treatment precautions. There is a huge convenience and consistency advantage over insecticides. (I am biased, but showing you why)

Last year with the help of the Agronomists and sales teams, LG Seeds participated in a large sampling rootworm adult beetle sampling program that was coordinated by Monsanto.
Data Summary and graghics are courtesy of Monsanto Technology, LLC.
travis rootworm composite

Note: 2 - 5 beetles per trap/day have been suggested as thresholds for predicting economic damage (Iowa State & University of Illinois)

Summary comments
In 2017 only corn after corn consistently met the threshold for needing rootworm control. 2016 was less extensively sampled but generally showed similar hot spots. Point of fact is that corn rootworms have not gone away, and the consequence of no or poor control are potentially real substantial yield loss.

There are two big questions that I can’t answer.

  • What’s the rootworm pressure going to be like in 2018?
  • What’s your risk tolerance?

One that I can answer:  Is the better choice a soil-applied insecticide or Trait Protection?
    Hands down – Trait Protection.

Note: The information in this issue is based upon field observations and third party information. Since variations in local conditions may affect the information and suggestions contained in this issue, LG Seeds disclaims legal responsibility therefore. Always read and follow label instructions.
LG Seeds and design are trademarks of SCA Limagrain.

Down a copy of this Technical Bulletin: Tech_368 - Corn Rootworm Management or Not