| Vol. 1 No. 1 | August 19, 1999 |
Corn Earworm Alert Continues for Southern Minnesota
Bill Hutchison, Extension Entomologist
Corn earworm (CEW): Based on "Pheromone Trap" data, CEW counts remained low this past week, at our Rosemount site (Dakota Co.) at about 10 moths/trap/night over the past 5 days. HOWEVER, at Blue Earth and Owatonna, VERY HIGH counts were recorded, with one trap exceeding 220/night on 8/10. This is a very high number, and again could very likely reflect emergence of local populations that arrived in July. My concern is that we are still about 7-10 days away from the usual migration flights that can exceed these numbers. Again, for CEW the pheromone traps work best; light traps catching 1-2 CEW moths/night can equate to anything from 10 to 200/night in pherm. traps. (Light traps can therefore be used as a rough "presence/absence" indicator of CEW, if interpreted properly).
This week, we developed a new www page to summarize CEW trap counts, from pherm. traps (click on address below). http://www.vegedge.umn.edu/CEW.htm This can also be accessed from the Welcome page of the VegEdge site.
The CEW site will be updated frequently Mon.-Friday, to closely track the flight over the next 3-4 weeks. We appreciate those cooperators who have agreed to call in their data. Any questions about the CEW data should be directed to Becky Hines (612-624-3670); she can also add a few more sites if others have CEW traps out.
Bottom line for CEW:
Spray programs initiated for much of the southern Minnesota sweet corn during
the past 10-12 days should be effective. However, for review:
Key crops affected=sweet corn; seed corn. In most years, much of our field corn
silks are starting to dry down, while sweet and seed corn fields may still have
fresh silks (through mid-Sept. for late sweet corn plantings). Insecticide
timing for CEW control is critical (MN understatement). CEW moths will be most
attracted to the nearest fresh-silking fields, from their emergence site, or as
new migrants coming in from southern U.S. The first spray, must be sprayed at
first silk (5-10%); a 2nd or 3rd spray should be applied at 60-80 Degree-day
intervals (=wide range from 3 days under high pressure and high temps. to 5-7
days under cooler weather).
Note: it may not pay to spray more than 2 times for seed corn (but, highly dependent on the value of a given hybrid, etc.).
Most eggs are laid directly on fresh silks; eggs hatch in 4-6 days with first instar larvae moving rapidly into the tip of the ear (e.g., in less than 30 min.). Once larvae are in the ear, say see ya later, ..... no insecticide will control these worms. Therefore, insecticide control works by killing some eggs directly (ovicidal control), but also by killing larvae as they hatch and/or move down the silk or plant. Thus, the longer residual activity on the silks the better. The more recent pyrethroids (Warrior, Baythroid, Capture) provide the most consistent control of CEW. These materials,along with Pounce or Ambush, will also provide good ECB control. NOTE: Asana (another pyrethroid) provides good CEW control, but only minimal ECB control. Thus, if both pests are present, do not use Asana! Finally, use of Lannate alone can be risky. For this approach to work, the grower must spray every 2-3 days (=residual activity of Lannate). Lannate is an excellent ovicidal material but has minimal residual activity for larvae, thus the frequent spray interval. Given the value of the crop, cost of material, and if high CEW are present, it may pay to tank mix a 1/2 rate of Lannate with a pyrethroid, for added ovicidal activity. Treatment is not necessary once silks turn brown, or the corn is within 7 days of harvest.
Although the Dipel and MVP B.t. products (Bacillus thuringiensis) work fairly well on European corn borer, they are not as effective on CEW. At this point, we really do not have many insecticide alternatives for CEW.
A CEW fact sheet, from Purdue, is available at the same, as a PDF File (need Acrobat reader).
Disclaimer
Reference to products in this publication is not intended to be an endorsement
to the exclusion of others which may have similar uses. Any person using
products listed in this publication assumes full responsibility for their use
in accordance with current directions of the manufacturer
Last Revised August 18, 1999.
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