Wet weather field crop pests, millipedes and slugs

Bryan Jensen, UW Extension and IPM Program


Because of the wet/cool weather, I’m sure a lot of people will be in fields focusing on corn and soybean emergence.  Although there are many potential causes for poor stands, millipedes are often looked at as a potential pest.  Millipedes are in the class Diplopoda and therefore, only somewhat distantly related to insects.  Millipedes have two sets of legs on most of the body segments and usually feed on decaying plant materials.  They are most common when field conditions are wet.

I rarely, if at all, think of millipedes as the primary cause of poor emergence.  Rather, they may feed on decaying seeds/seedlings that are already compromised by other pests or environmental problems.  However, they are easy to find close to the decaying seed and are often considered “guilty by association”.  Although I will not rule out the possibility of millipedes, I would want to focus on all the other possibilities before settling on millipedes. Quickly jumping to a conclusion may prevent finding what the real cause is.


Not all that unexpectedly, slug calls have started.  Both soybean and corn are susceptible and once the field is planted, preventive options (tillage, residue control, rotation, not using a neonic seed treatment, seed furrow closure, etc.) are no longer available and focus must be on rescue.  Unfortunately, relying on baits and other rescue treatments may not provide economical (or acceptable) control.  An integrated approach using prevention is always preferable.

Non-chemical options including row cultivation isn’t always possible, reliable or practical.  Effective weed control can help but is already part of your best management practices.  Some people have tried spraying liquid fertilizer solutions at night with mixed results.  I have had no experience with this practice but can see some problems including lack of replicated research, high costs and that multiple applications may be needed for a lethal dose.  Control is by contact only, there is no residual control.

Insecticides will not work.  Slug baits can be effective but given tight profit margins they might not be an option depending on severity of infestation.

Economic thresholds do not exist for slugs.  Before baits are considered, thoroughly read the label.  The metaldehyde-based baits labels that I have read exclude soybean use in Wisconsin.  This is not obvious because a you must read a footnote which indicates states that are approved for use.  The Sodium Ferric EDTA containing product (Iron Fist) comes with precautions as well.  Although labeled for corn and soybean production in Wisconsin, it must be applied between the rows at the seedling and later stages of crop development.  Furthermore, it’s availability is restricted in some Midwestern states.

One of the best options available right now may be patience and the hope that summer-like dry weather will arrive.

UW IPM has a video about slug damage and scouting, see below.