The adaptation of a biotype of western corn rootworm (WCR) to first year field corn following soybeans is a new problem impacting Ohio agriculture. This problem initially developed in northeast Illinois and has been moving eastward during the past decade. First year corn rootworm (FYCR) activity in western Ohio counties was detected in 1996. Field surveys in 1997, confirmed FYCR activity in Mercer, Paulding, Shelby and Van Wert counties. In addition, cases of rootworm injury on first year corn were observed at a number of locations in Ohio raising questions in regard to the dispersal and potential for economic injury by this new pest problem throughout the State.
Given the need for additional information on FYCR activity in Ohio, a collaborative FYCR survey effort was initiated in the summer of 1998 to monitor adult WCR activity in soybean fields. Survey participants included corporate personnel (American Cyanamid, Dow AgroSciences & Pioneer Hybrids), Ohio Independent Agricultural Crop Consultants, and OSU Extension. The common method selected for monitoring FYCR in soybean fields was the Pherocon AM yellow sticky trap for which the University of Illinois has demonstrated a relationship between WCR beetle catch and potential rootworm injury on corn following soybeans. Collection of 2 or more WCR beetles per Pherocon AM trap per day in a soybean field is presumed to indicate a potential for economic injury at a root rating level of 3 if corn is planted the following year. For each soybean site monitored, four Pherocon AM traps were deployed at biweekly time periods from mid-July through late August. The collaborative survey effort resulted in the monitoring of over 582 soybean sites distributed among 69 counties in Ohio.
The results of the 1998 FYCR survey demonstrated very low levels of WCR beetle activity in most of the 580 soybean sites monitored with the exception of a few counties in northwest Ohio adjacent to the Indiana border. Field sites having an average catch of one or more WCR beetles per trap per day (e.g. 50% threshold level) were limited to Williams, Defiance and Van Wert counties. WCR catches from sites in Henry, Paulding and Fulton counties ranged from 0.2 to 0.5 WCR/trap/day (e.g. 10% to 25% threshold level). In other western and northwestern counties, average catches of WCR ranged from 0.05 to 0.2 WCR/trap/day (e.g. less than 10% threshold). In the remainder of the State, average WCR catches remained less than 0.05 WCR/trap/day, except for a few sites in Tuscarawas and Wayne counties where above normal WCR catches are likely due to the dispersal of WCR across smaller soybean fields (see Table 1).
At 30 of the field survey sites, OSU Extension personnel monitored adjacent soybean and corn fields using both Pherocon AM and Multigard traps in soybeans, Multigard traps in corn, visual counts of CRW beetles in corn, and sweep net collections of beetles in soybeans to enable comparison of rootworm activity observed in 1998 to that observed in previous field surveys. In Multigard trap collections of WCR from seven farms monitored in both 1997 and 1998, collections of WCR beetles in corn fields declined more than 50% and collections of WCR in soybean fields declined almost 90%. Such a decline in WCR activity may be due to a low rate of survival of the immature larvae during the growing season or possible a high rate of mortality of the over-wintering egg stage during a mild winter. Whatever the reason, adult rootworm activity in 1998 is lower than normal and the potential for offspring leading to rootworm injury in corn next year should decline proportionately until environmental conditions favor a recovery in rootworm activity.
In respect to northern corn rootworm (NCR), the intensive surveys of first year corn detected cases of unusual NCR activity indicating a possible problem of extended diapause causing economic injury in first year corn rotated with soybeans. Corn sites surveyed in Paulding and Putnam counties exhibited unusual NCR activity which was as high or higher than WCR adult activity, and economic root system injury was observed. Thus, it should be recognized that rootworm problems in first year corn may be due to the new FYCR problem, extended diapause of NCR, or a combination of the WCR and NCR activity.
In summary, rootworm may or may not be a problem on first year corn depending on a set of conditions ranging for geographical location to annual variations in rootworm activity influenced by climatic variables. In the current year, the geographical gradient of significant FYCR activity appears to have retrenched to a limited region along the northwest Ohio border with Indiana. However, given favorable conditions, rootworm activity could rebound to problem levels over a wide area within a year or two. However, it should be recognized that pest management strategies should be developed over time to meet the specific conditions associated with a specific geographical area.
In regard to rootworm management, if soil insecticides are applied at planting time for rootworm control, then check strips should be maintained to determine whether the treatment was warranted or not. If soil insecticides are not applied to first year corn for rootworm control, then soybean fields targeted for corn the following year should be monitored with yellow sticky traps or sweep net sampled during late July and August to detect adult rootworm activity indicative of the first year corn rootworm problem. In addition, root systems of first year corn fields should be inspected in July to determine the presence of rootworm injury. If a potential rootworm problem is anticipated, but the need for soil insecticide treatment of first year corn is in question, then a management program including a combination of treated and untreated corn should be followed until an appropriate rootworm management strategy is selected based on local field observations.
| No. Sites | Avg. WCR | Percent of Sites Having Avg. Catch | |||
|---|---|---|---|---|---|
| County | Monitored | /Trap/Day | (0.2) | (0.5) | (1.0) |
| Defiance | 21 | 0.59 | 76 | 43 | 19 |
| Van Wert | 14 | 0.55 | 86 | 36 | 14 |
| Williams | 14 | 0.49 | 100 | 36 | 7 |
| Henry | 16 | 0.26 | 44 | 19 | 0 |
| Paulding | 5 | 0.26 | 80 | 0 | 0 |
| Fulton | 12 | 0.21 | 42 | 8 | 0 |
| Mercer | 8 | 0.16 | 38 | 0 | 0 |
| Darke | 39 | 0.15 | 31 | 3 | 0 |
| Preble | 7 | 0.10 | 29 | 0 | 0 |
| Shelby | 18 | 0.10 | 17 | 0 | 0 |
| Tuscarawas | 7 | 0.09 | 29 | 0 | 0 |
| Putnam | 14 | 0.08 | 0 | 0 | 0 |
| Hancock | 16 | 0.08 | 0 | 0 | 0 |
| Butler | 7 | 0.07 | 14 | 0 | 0 |
| Champaign | 10 | 0.07 | 10 | 0 | 0 |
| Auglaize | 8 | 0.07 | 13 | 0 | 0 |
| Logan | 4 | 0.07 | 0 | 0 | 0 |
| Wayne | 12 | 0.07 | 8 | 0 | 0 |
| Hardin | 12 | 0.07 | 17 | 0 | 0 |
| Wood | 12 | 0.05 | 0 | 0 | 0 |
| Allen | 12 | 0.05 | 0 | 0 | 0 |
| Portage | 3 | 0.05 | 0 | 0 | 0 |
Counties with average catch of 0.04: Morrow (no. sites = 5), Stark (6), Seneca (13), and Sandusky (15). Counties with average catch of 0.03: Highland (4), Erie (9), Miami (7), Columbiana(3), Knox (14), and Coshockton (5). Counties with average catch of 0.02: Licking (4), Madison (12), Ashland (6), Medina (4), Montgomery (7), and Ross (2). Counties with average catch less than 0.02: Marion (9), Crawford (13), Ottawa (4), Wyandot (6), Pickaway (19), Fairfield (23), Clark (10), Richland (3), Clinton (13), Union (4), Huron (6), Fayette (19), Carroll (4), Brown (4), Greene (4), Delaware (4), Warren (8), and Washington (3).
Note: Counties having less than three sites monitored have been excluded from this listing.
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