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Black cutworm scouting advisory

By Staff | May 9, 2012

THE MAP ON this page shows the predicted cutting dates for Iowa climate divisions. Where there are two dates, the top date is an estimate based on moth captures that occurred near the end of March; all other dates are based on mid-April captures.

AMES (ISU) – With the unseasonably warm temperatures occurring earlier this year, we asked black cutworm monitoring participants to place moth traps during the end of March. The first moth was recorded in Muscatine County on March 20.

Peak flights have been reported by cooperators in many parts of Iowa this year. Iowa State University advisers predict cutting dates – the date when black cutworm larvae are likely to be damaging corn – are based on recorded peak flights which took place near the end of March and approximately two weeks later in Iowa.

Since the early peak flights near the end of March, freezing temperatures have been observed in Iowa. However, there is evidence to suggest that black cutworm eggs are able to survive for at least one night of sub-freezing temperatures. So it may be that these peak flights recorded in late March will produce cutting larvae; however, scouting a field is the only way to tell if an economic infestation is occurring in an emerged crop.

Trap data also shows that moths have been observed flying into the state at other times during April than the posted peak flights. Because of this, black cutworm larval activity may occur before and/or after the estimated cutting dates. Growers are urged to scout fields on a regular basis as scouting is the only way to tell if a field is infested by black cutworm larvae.

Black cutworms are light grey to black, with granular-appearing skin and four pairs of fleshy prolegs on the hind end.

They can be confused with another insect that may be found in fields during spring, the dingy cutworm. However, there are some characteristics that can help to set species apart.

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