As some extra-early plantings of sweet corn are beginning to reach the silking stage, growers should have a plan for managing caterpillar pests. Pheromone traps at various locations around Ohio have been detecting some corn earworm moths, as well as moths of the European corn borer. This timing of the European corn borer moths is as expected in an average year, but the presence of corn earworm this early is not typical and is a concern. Trap reports can be accessed on the internet using this link: http://u.osu.edu/pestmanagement/trap-reports/vegetable/
The key expected pest of early sweet corn in Ohio is the European corn borer (ECB), although it has been present at lower density during the past 10 years compared to earlier years, most likely due to the widespread use of transgenic B.T. field corn in the midwestern USA. In early sweet corn, ECB moths typically emerge from their overwintering locations and start laying eggs in whorl-stage corn. As tassels develop, the ECB larvae move into tassels to feed. As ears begin to form, ECB larvae can either drop from the tassel to the tip of the ear, or they can burrow down the stalk and enter the ear at the shank end. These ECB larvae are best controlled by one or two applications of an insecticide during the emerging tassel stage. On farms with plantings of extra-early corn, ECB moths can be emerging and searching for egg-laying sites once silk is present; in this case, they do not infest plantings with whorl-stage corn but instead they are attracted to the most advanced plantings where they lay eggs in the ear zone. These need to be managed by a series of sprays at 5-day intervals during the silking period.
On farms at which corn earworm (CEW) is present, as detected by pheromone traps, a more aggressive insecticide program is needed than when only ECB is present. Sprays every 2 to 5 days during silking are needed, with the interval depending on the pest pressure and temperature (details available with this link: http://u.osu.edu/pestmanagement/files/2014/12/CornTrapInstructions2009-u47rp3.pdf ). Although pyrethroid insecticides such as Warrior, Hero, Mustang Maxx, Baythroid, and permethrin are effective for control of ECB, they are no longer highly effective for control of CEW. Trials in Ohio have shown that Warrior used at the maximum rate is generally still effective for CEW control when the CEW pest pressure is low, but not effective when pest pressure is high. Alternatives to the pyrethroids are Coragen, Radiant, Lannate, and Blackhawk. Besiege is the new name for the pre-mix product formerly known as Voliam Xpress; this has the same active ingredients as in Coragen plus Warrior. Besiege is useful when silk clipping beetles (Japanese beetle and rootworm beetles) are present at the same time as caterpillar pests, which is typically in early July. Organic growers can spray Entrust or sprayable B.t. such as Javelin or Dipel.