Corn Earworm Moth Season Is Here: Sweet- Or Field-Corn?

The first significant flights of corn earworm (CEW) moths have been detected this past week at several southern MN locations, including Sleepy Eye and at our Agric. Expt. Station, Rosemount, MN.  Although moth counts are still low (<10 moths/night), Blue Earth has reported two significant catches, and traps should now be deployed if not already out, and moth catch should be monitored closely.  As the name implies larvae most often develop in the ears of field and sweet corn (Fig. 1), although some early-season flights will survive on whorl stage corn. Recent research in our lab confirmed that CEW cannot successfully overwinter in Minnesota, or at latitudes >40 (roughly north of I-80 in the Midwest states), and must therefore migrate north each summer from the southern states. Although this is another pest with a wide host range, both field corn and sweet corn are two of the most preferred hosts.  Fortunately, for field corn producers, most of the corn has completed its silking phase by the time CEW moths begin migrating into Minnesota (late July – early August).  

 

For both fresh-market, and processing sweet corn, however, CEW can cause considerable damage and losses in marketable product. As noted, once 1-inch size larvae are present in the ear tip, and usually protected by husk cover, it is too late for control options. This is the reason we emphasize trapping to know when moths are coming into the state, or better yet, when they are being caught on or near your farm.  Because of the late CEW arrival, producers can experience considerable savings in insecticide costs by knowing they do not need to spray early-season. Once CEW arrives, insecticidal sprays should be initiated when moths are averaging 5 to 10/night, for at least 2 consecutive nights; the range in thresholds reflects a growers personal risk tolerance (and market conditions). The challenge for managing this pest is that the majority of eggs are laid directly on fresh silks, and at current summer temperatures, the larvae hatch in 4-5 days, then proceed to move quickly down the silk channel into the ear tip.  Unfortunately, we do not have reliable biological controls for CEW, although the minute pirate bug (Orius spp.) are common in MN, and are known to be effective egg predators on the ear tips/silk tissue.