Rapid Rise in Corn Earworm Population
Posted: August 8, 2012
DRAMATIC and RAPID increases in corn earworm captures are occurring. Spikes were detected in Blair, Bucks, Centre, Lancaster, Montgomery, Washington, Westmoreland, and York. All of these sites exceeded or closely approached thresholds that suggest a 3-to-4 day spray interval, starting at early silk and continuing (if trap counts continue to be moderate to high) to about 7 days prior to harvest. It is not uncommon for plantings to receive 5 sprays (sometimes more) to manage the types of numbers along with the rapid increase being reported in some of these locations. Similar and higher spikes were reported from Virginia, Maryland and Delaware, and even Long Island. Patterns of increase showed up as far north as Maine.
Clickable maps to display this are at www.pestwatch.psu.edu. Go to the interactive maps tab. Click on sites to see the time series graph at that site. Use the zoom bar and time bar to focus your view. Toggle the legend buttons if you want to turn off the sites without data for a given date.
Some growers have reported problems with reliance on pyrethroid insecticides to control high earworm populations. Insecticides with newer modes-of-action are helpful for high populations – these include chlorantraniliprole (Coragen, or part of Volium Xpress), flubendiamide (Belt), and spinetroram (Radiant). Older materials that do not rely solely on pyrethroids include Cobalt Advanced (which includes chlorpyrifos) and Lannate (which is methomyl). Bt sweet corn that relies only on the cryIA family of genes should not be viewed as sufficient to control high earworm populations, although many fewer sprays (1 or at most 2 sprays) has worked very well in trials in Pennsylvania.