Issue No. 13, Article 2/June 20, 2008
Japanese Beetle Captures Reported in Southern Illinois: Expectations for 2008
Ron Hines has reported that captures of Japanese beetle adults are beginning to increase in pheromone traps located in Franklin and Pulaski counties. On June 17, beetle numbers reached 238 (Franklin) and 191 (Pulaski) adults per trap. No captures of this insect were reported for Marion, Sangamon, and St. Clair counties through mid-June. As Ron indicated (www.ipm.uiuc.edu/pubs/hines_report/), these captures are lower than in previous years and approximately 2 to 3 weeks later.
So what are the potential implications of this later emergence? First of all, let's hope that the lower number of beetles continues throughout the growing season. Second, I believe producers will need to be vigilant with respect to potential silk clipping this year, as peak densities of Japanese beetle and corn rootworm adults may coincide with the period of silking and pollination. As reported previously in the Bulletin, corn rootworm hatch was delayed slightly this season. With the significant delays in planting this year, the most critical period of corn development will likely be pushed into mid- to late July for many fields, generally the hottest period of the summer. If peak densities of corn rootworm and Japanese beetle adults are present during this time frame, fields will require careful monitoring for evidence of excessive silk clipping. Let us know when you begin to detect corn rootworm or Japanese beetle adults in your fields and we will share these observations with our readers.
In addition to concerns about silk clipping and Japanese beetle adults, soybeans will require careful scouting this year as well. The traditional defoliation levels suggested as economic thresholds are 30% before bloom and 20% between bloom and pod fill. Due to the increasing value of this year's soybean crop, these numbers most likely require a more conservative assessment as treatment decisions are pondered. Economic injury levels fluctuate according to a number of economic and biological parameters. For a more complete discussion on this topic, please refer to an article published in the first issue of the Bulletin this season.--Mike Gray