In the last day Central Valley Agronomists have come across a few fields of Conventional and herbicide resistant corn have been attacked by Armyworm.
Armyworm Moths tend to lay their eggs in grassy areas, (Small Grain, CRP fields, ditches, corn fields with heavy grass pressure) and tend to prefer to eat grass when the larvae hatch. I have been told by several sources that Armyworm will attack the grass in a broadleaf crop (Soybean, Sunflower) and leave the broadleaf crop alone.
Fields or areas that I would be scouting would be:
- Small Grain
- Sweet Corn
- Conventional Corn
- Fields with a History of Grass issues
- Small Grain or Grass Cover Crops
- Refuge Corn (No Insect Resistance, straight Roundup or Liberty)
- Ditches or Field Margins
Armyworm larvae tend to be more nocturnal and will tend to congregate in the whorl of corn plants but will also hid in crop residue during the day. This tends to make them a little more difficult to find.
If your corn is SmartStax or has Herculex (Unless Herculex RW/RR2 or HerculexRW) in it you do have a level of protection from Armyworm. Other traits that offer protection are Genuity VT Double PRO and Triple PRO, but some of the older genetics that offer YieldGard VT Triple are susceptible to Armyworm. Please check with your local Central Valley Agronomist to clarify the level of protection against Armyworms your hybrids have.
Even with built in protection in the plant, if we have a heavy infestation of Armyworm as we have recently encountered it could overwhelm the plant even with that protection. The concern here is that the pest needs to ingest part of the plant before control will be achieved, if enough pests ingest the plant, the plant will be overrun. The analogy is you might have food for 50 people but if 150 people come to eat you will run out of food fast.
Treatment levels in Small Grain fields are 4-5 larvae/square foot after the plants have been shook. Treatment levels for corn are when 25% of plants have 2 larvae in the whorl or when 75% of plants have 1 larvae or more.
The potential reason for this influx of Armyworm is that our cool spring may have been detrimental to the flies and wasps that feed on Armyworm larvae as well as fungal or virus’s that tend to infect larvae in warmer environments.
Again if you have more questions regarding Armyworms contact your local Central Valley Agronomist
