There have been several reports about treatment level, and in some cases very high, infestations of southwestern corn borer in non-Bt corn.  I’ve written a few recent articles about dealing with this pest (see links below).  There are a few other reminders also listed below.

Related Articles:
Scouting for Southwestern Corn Borer
Moth Trapping … Southwestern Corn Borers Are Out Early

Application Tips For Whorl Stage Corn:

1. Treatment is suggested when 15% or more of whorls are infested
2. Time applications before most larvae begin stalk tunneling
3. Increase volume as much as practical but no less than 10 GPA, trying to get the spray into the whorls
4. Timing of application is more important than insecticide selection
5. Pyrethroid insecticides such as Asana XL, Baythroid XL, Brigade or other bifenthrin products, Declare, Karate/Warrior, Mustang Max or others at mid- to high-labeled rates are good choices for whorl stage corn.

Intrepid, Belt, Prevathon and Besiege are preferred insecticides for use in tasseling corn where their residual and rainfastness often pay off.