Western bean cutworm update for August 2, 2011

An update on western bean cutworm activity in corn, as well as spray recommendations for central Michigan dry beans.

Cutworm flight may have peaked the week of July 24, but the peak seems messier than the last two seasons, with some locations dropping, but others still going strong. In 2010 (one of the hottest on record), the peak clearly was during the week of July 25. In 2009 (a cool season), the peak occurred later during the week of August 8. The map of accumulated totals by county is posted at the MSU Field Crops Entomology website.

Corn

In the corn we scout in central Michigan, egglaying has tapered off in tasseling fields. Many of the egg masses collected one to two weeks ago did not hatch fully, and some didn’t hatch at all (many masses were also small). This week, the egg masses seem larger and healthier (no hard data, just an impression from hours spent collecting them).

I believe that moths took a hit during the hot, dry weather one to two weeks ago. Female moths do not feed, but need water to survive and make eggs. Under hot, dry conditions, many moth species will simply reabsorb the developing eggs into their body to use as water to survive, so it makes sense that we observed fewer or smaller egg masses when it was 90-plus degrees. Hot, dry conditions can also simply stress moths (reducing overall egglaying and increasing death) or dry-out eggs (reducing the percent hatch).

Now that the 90 degree heat has past and some areas received rain, surviving moths may be back in business, getting adequate moisture and depositing larger, healthier egg masses. Females will now be attracted to younger corn fields and dry beans.

Spray recommendation for dry beans

Now is the time to spray dry beans in the central production area, including Arenac, Gladwin, Gratiot, Isabella, Kent, Mecosta, Montcalm, and counties to the north. The highest priority fields are those with the biggest canopy (earliest planted, narrow rows), especially if irrigated, on sandy, well-drained soil (traditional western bean cutworm “hot spots”), or near tasseled, older corn. Beans that were late-planted, smaller and drought-stressed, or surrounded by large amounts of young corn, are a lower priority.

The week of August 1 is an ideal time to spray high priority fields, but note that from past research we know that even a spray that goes on a bit later decreases pod and bean damage, and increases quality.

Dr. DiFonzo’s work is funded in part by MSU‘s AgBioResearch.

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