Corn Rootworm on First Year & Continuous Corn
Visual observations and trap collections of both western corn rootworm and northern corn rootworm adults indicate an increase in adult corn rootworm activity compared to that of 1998. Rootworm activity declined in 1998, but field observations during the 1999 growing season indicate a revival of rootworm activity. Due to relatively low levels of adult rootworm activity in 1998, rootworm injury to corn caused by larvae feeding was often low this year.
A major corn pest problem spreading across Ohio is the first year corn rootworm (FYCRW), which is the new biotype of the western corn rootworm that deposits eggs in soybean fields which subsequently impact first year corn. To address this problem, OSU Extension personnel cooperating with consultants and agri-business representatives have implemented annual statewide survey programs to evaluate the activity of adult rootworm in Ohio soybeans. The program uses Pherocan AM yellow sticky traps, which are deployed in soybean fields (at least 4 traps per field) on a biweekly schedule from mid-July through late August to monitor adult rootworm activity. The number of fields monitored in 1999 totaled 395 soybean fields.
Status of First Year Corn Rootworm Activity in Ohio
A summary of average catches of WCR adults per trap per day for the 1999 growing season is presented in Table 1. The catch for a given field represents the average catch of adult WCR in four traps over a six week time period. The average catch for a county represents the total number of sites monitored in a given county.
It is important to note that in WCR adult catches. Areas lacking FYCRW activity generally exhibit very low averages (less than 0.10). As FYCRW moves into a county, the average WCR catch begins to exceed 0.20, or one or more sites exhibit an average catch exceeding 0.50 WCR per trap per day.
Currently the range of FYCRW activity is assumed to range from Williams County down to Darke County along the Indiana border, and the eastern edge of activity may be drawn from Fulton County to the western side of Champaign County.
Table 1. Ohio counties having an average catch 0.1 or more WCR per trap per day.
| County | No. Sites | Percent of Sites within Catch range | Average Catch | |||
| Monitored | >= 0 | >= 0.2 | >= 0.5 | >= 1.0 | No. WCR per Trap | |
| < 0.2 | < 0.5 | < 1.0 | per Day | |||
| Henry | 10 | 50 | 30 | 10 | 10 | 0.62 |
| Van Wert | 20 | 20 | 30 | 50 | 0 | 0.44 |
| Mercer | 9 | 22 | 67 | 11 | 0 | 0.35 |
| Darke | 23 | 30 | 44 | 26 | 0 | 0.34 |
| Defiance | 12 | 42 | 50 | 8 | 0 | 0.30 |
| Paulding | 7 | 43 | 43 | 14 | 0 | 0.30 |
| Williams | 14 | 57 | 43 | 0 | 0 | 0.24 |
| Allen | 9 | 56 | 33 | 11 | 0 | 0.22 |
| Auglaize | 9 | 56 | 44 | 0 | 0 | 0.20 |
| Shelby | 9 | 33 | 67 | 0 | 0 | 0.19 |
| Champaign | 9 | 78 | 11 | 11 | 0 | 0.18 |
| Putnam | 13 | 54 | 31 | 8 | 0 | 0.17 |
| Fulton | 9 | 67 | 33 | 0 | 0 | 0.14 |
| Greene | 4 | 75 | 25 | 0 | 0 | 0.14 |
| Hardin | 6 | 83 | 17 | 0 | 0 | 0.13 |
| Logan | 4 | 75 | 25 | 0 | 0 | 0.13 |
| Preble | 6 | 83 | 17 | 0 | 0 | 0.13 |
| Wayne | 7 | 86 | 14 | 0 | 0 | 0.11 |
Fulton and Shelby Counties are regarded as positive for FYCRW based on surveys conducted in 1997 or 1998.
Soybean fields in thirty-nine additional counties were monitored during the 1999 field season. Two-thirds of the sites monitored had an average catch of less than 0.20 WCR per trap per day which is less than 10% of the threshold level of 2.0 WCR per trap per day which is regarded as an indicator of potential economic rootworm injury in field year corn following soybeans. Only one site in Henry County exhibited an average catch exceeding the level of 2.0.
This survey included cooperation from Pioneer (113 sites surveyed), Ohio Agricultural Independent Crop Consultants (95 sites surveyed), Cyanamid (77 sites surveyed), OSU Extension (111 sites surveyed) and financial support from Dow AgroSciences.
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