Personnel from Ohio State University Extension continued to sample for western corn rootworm adults (WCR) in soybean fields for the tenth year. Data from the 2006 rootworm trapping program have been assembled. This is an overview of the results from that survey. Sampling was done using Pherocon? AM yellow sticky traps placed in 88 fields covering 25 counties ( see map). Six traps were placed in the soybeans on metal posts at canopy height and located at least 100 feet from the field edge and evenly spaced in the field. The traps were initially placed in fields in mid-July and removed in late August or early September. Traps were serviced once a week throughout the sampling period with a new, clean trap. After each trapping week, the numbers of beetles collected were summed and divided by the number of traps (6) and the number of days the traps were in the field resulting in the average number of beetles collected per trap per day.
A summary of the weekly catches of WCR adults per trap per day from the 2006 growing season can be found on the web in Table 1 . Research indicates that catches in soybean of 5 or more beetles/trap/day during any trapping week indicates a potential problem with rootworm in the field the following year.
The trapping data from 2006 had the following results from the 86 fields:
After rounding results to the nearest whole number, nineteen fields had an average of 5 or more beetles/trap/day and five fields had an average of between 4 and less than 5 beetles/trap/day. The rest of the fields were less than 4 beetles/trap/day.
Fields with 5 or more beetles/trap/day were in Allen, Champaign, Crawford, Darke, Defiance, Hardin, Miami, Paulding, Putnam and Van Wert Counties. Those fields between 4 and 5 beetles/trap/day were in Allen (1), Miami (1), Paulding (1) and Van Wert (2) Counties.
So What Does This Mean?
The trapping data from 2006 was at the highest level we have seen in the 10 years that trapping has been conducted. It is not difficult to make recommendations about the fields that were trapped in 2006 because, based on research, if a field has a beetle count of 5 or more beetles/trap/day during any trapping week, the field will need to be treated for rootworm if it is planted to corn in 2007 (see newsletter article for treatment options).
The problem becomes when a decision needs to be made about fields that were not trapped. We know that there are probably more fields that need to be treated and at the same time, fields that will not need treatment. Since there isn't any way to predict which fields need treatment without trapping information, we would suggest that producers take into account several things before a decision is made about treatment needed on the field. Things that can be used to help make the decision are:
1) Are the fields located in a county with low or high counts in 2006? We cannot use a few trapped
fields in a county to make countywide recommendations but it does give some idea of the level of
rootworm activity in the area.
2) Has there ever been a problem with the western corn rootworm variant in the field in the past?
3) Were there any direct observations of root injury and lodging due to rootworm activity in your own
adjacent corn fields during the 2006 growing season?
4) How wide spread was the injury and lodging within the fields? Was it a small localized spot or across the entire field?
5) Were there any severe weather events that could account for the observed lodging?
6) Did the lodging have a significant impact on yield or economic returns?
7) Since there are no rescue treatments for rootworm larvae, how much risk can be tolerated?
We also suggest if a field is treated for the western variant next year, that several untreated strips be left in the field. This will be the only way we can tell if the western variant is a problem in the field. Because of this continued concern with this insect, we urge growers to develop a sampling plan next year in their soybean fields, and to sample roots for feeding injury in their first year corn for the presence of the western variant.
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