- Author: Luis Espino
I have received reports of significant defoliation due to armyworms from several areas: Glenn, Colusa, Butte and Yolo counties. In most areas the defoliation is severe but the area affected within fields still small.
I inspected a field in Glenn County. The defoliation was severe along levees and in near borders, and worms were about 5th instar. Population was high, similar to 2015.
Severe defoliation along levee.
Severe defoliation along border of field.
Fifth instar armyworms in Glenn County field, 21 June 2017.
The degree day model predicted 5th instar armyworms will start showing up June 22. The heat from last week sped things up, but the model was really close.
Remember that worms feed the most during 5th and 6th instars, and it will take them 10 days to complete their cycle after reaching the 5th instar. This means that there is plenty of time for them to cause more injury and move to other areas of the field. Keep a close eye and consider a treatment if the worms are still present. Do not wait until worms get bigger, they are harder to kill with any insecticide. It's starting to look like 2015./table>