Invertebrate Pests are Making their Presence Known

Posted: June 7, 2017

This spring has been different and odd enough in many parts of Pennsylvania that folks are looking for a return to normal, whatever that means. Most calls and other communications that I have received from farmers have had to do with slugs, but other invertebrate pests are also active and I will mention them briefly today.
Figure 1. Slug-damaged corn plants (Photo by Andrew Frankenfield, Penn State Extension).

Figure 1. Slug-damaged corn plants (Photo by Andrew Frankenfield, Penn State Extension).

First, let’s deal with slugs in a bit more detail. Many folks are calling me about rescue treatments available for slugs and, of course, there are limited options. One viable option that should be acknowledged is to do nothing, particularly for slugs in corn. My research group has tried to find a relationship between the amounts of damage that corn plants experience and the productivity of that plant, and we have yet to detect one. Intuitively, one would expect that as the amount of slug damage goes up, plant productivity would come down, but this is not what we found. We found that undamaged corn plants can be as productive as ones that looked hammered from slug feeding. With this information in mind, I encourage farmers to manage for stand success. If plants are still growing and new growth has less feeding damage than old growth, things are going in the right direction and slug populations may not need to be managed; hope for dry weather and come back to check on that field later in the week. The same philosophy (i.e., managing for stand success) can be used for soybeans, but plants are more vulnerable to being killed by slugs because their growing tip is above ground. At the same time, soybeans have more plants per acre and stands can be found if some plants fail, but there is a balancing act here that farmers need to consider.

If stand success is at risk, then using metaldehyde-based baits or nitrogen solutions may be a good idea. I address these options in our slug factsheet, but keep in mind that their success will have a lot to do with the coming weather. Baits, for example, tend to be water soluble and rain will wash away some of the product. I recommend that baits be used over a small area where the product can be spread well (4-6 pellets per ft2) to help ensure stand survival in the worst part of a field; trying to protect entire fields with baits is expensive and a recipe for frustration. Another option is spraying Lannate, for which DuPont issued a 2(ee) Recommendation for using it in corn and soybeans in Pennsylvania, Delaware, Maryland, Virginia, and West Virginia. Such a recommendation allows for uses of a pesticide that are consistent with its labeling; however, using Lannate (or nitrogen sprays) can be challenging with rain because they are contact poisons with little to no residual. Unfortunately from the efficacy data I have seen for Lannate, I am not confident it will provide the control that growers seek. I am also concerned about non-target effects because its active ingredient is methomyl, which is a carbamate insecticide, and carbamates are notorious for their broad spectrum toxicity to invertebrates, including beneficial insects, spiders, and earthworms. The best remedy for slugs, however, will be dry weather and sunny skies to force the slugs to hide for the summer!

I have also received a good number of phone calls from growers experiencing black cutworm, armyworm, and cereal leaf beetle. As a reminder, from our Black Cutworm Monitoring Network we can say that most of state should be seeing cutting damage in corn if it is going to materialize. It is past time to be scouting for black cutworm, but while you are out there, also look for armyworm in corn, hay, and small grains and cereal leaf beetle in small grains. I have written about these in previous newsletter articles, but just want to remind growers that they are active and you do not want to overlook them. Good luck scouting!

Contact Information

John Tooker
  • Extension Specialist
Phone: 814-865-7082