The usual scouting and threshold recommendations do not apply for row cover, plastic, or transplanted sweet corn that is close to tassel emergence during the first generation flight of European corn borer (ECB).  In these early plantings, larvae don’t feed in the whorl and emerge in the tassel as they do in bare ground corn.  Below are suggestions for timing sprays in season extension corn.

Sweet corn started under row cover with traps set up along the edge.

Moths will be most attracted to, and deposit the most egg masses in, the most advanced corn, especially fields started under plastic or row cover. Corn that is in late whorl to tassel emergence stage when egg masses are being laid does not show the typical larval feeding in the emerging tassel that we see in bare ground corn that is in the whorl stage during the flight. For this reason, tassel emergence scouting and thresholds have not been successful in plastic and row cover corn.  Target newly hatching larvae using the moth trap catches or scout for egg masses to determine when sprays are needed.  Growers have had good results when pheromone trap catches were used to time sprays for the first generation ECB in row cover or plastic corn. Growers waited until there was a significant increase in the ECB trap catches in their area and then timed sprays to coincide with egg hatch.  ECB eggs require 100 degree days (base 50) from oviposition to hatch.  Two to three applications bracketing the peak moth flight are generally effective

Degree day calculations for many locations may be found on the NEWA web site: http://newa.cornell.edu