Soybean N relations and bean leaf beetle larval feeding damage

Authors: Riedell, Walter; Lundgren, Jonathan; Osborne, Shannon; Pikul Jr, Joseph

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/15/2006
Publication Date: 11/13/2006
Citation: Riedell, W.E., Lundgren, J.G., Osborne, S.L., Pikul Jr, J.L. 2006. Soybean N relations and bean leaf beetle larval feeding damage. Meeting Abstract for ASA/CSSA/SSSA Annual Meeting, Indianapolis, IN, November 13-16, 2006.

Interpretive Summary: Economic thresholds for bean leaf beetle on soybean have been established on the basis of damage to above-ground parts of soybean plants. The economic importance of larval feeding on roots and nodules is not fully understood, although this kind of injury is likely to have a serious impact on yields. In the northern Great Plains, N starter fertilizer applied to soybeans planted in late May reduced ureide levels (ureides are indicators of N fixation through mid July. Because soybean root nodules are an important food source for bean leaf beetle larvae and because first generation adult beetles begin to emerge from soybean fields in mid-July (Catangui 2003), it is possible that soil management tactics that affect soybean nodulation, such as starter N application, could have an effect on bean leaf beetle biology. Our objective was to investigate the potential relationships between soil N management, soybean N relations, and bean leaf beetle biology. Our findings suggest that, because the soybean planting date was postponed 3 weeks due to inclement weather, the soil N management treatments imposed during the 2005 growing season had little effect upon ureide-N concentration. This suggests that there were few differences in soybean root nodulation and atmospheric N fixation across treatments. Thus it was not surprising to find that there were no major effects of soil N management treatments on bean leaf beetle larval populations. Additional data over multiple years are needed to properly test our hypothesis.

Technical Abstract: This study was conducted to determine if soil fertilizer nitrogen (N) input treatments would impact the bean leaf beetle (Cerotoma trifurcate Förster) biology. The experiment was conducted in the soybean [Glycine max (L.) Merr.] phase of a long-term corn (Zea mays L.) and soybean rotation study. Soil N input treatments were: corn fertilized for a yield goal of 8.5 Mg/ha (high N input), 5.3 Mg/ha (medium N input), or corn not fertilized (no N input). Corn and soybean plots also were treated with banded starter fertilizer (112 kg/ha) as 14-16-11, 7-16-11, or 0-16-11 elemental N-P-K on the high N, medium N, and no N input treatments, respectively. First generation larvae from the medium and no N input plots had significantly larger body size than larvae from the high N input plots. Head capsule widths of first generation beetles from medium N input plots were significantly larger than beetles that emerged from the other N input plots. Soybeans grown on high N input plots showed higher shoot nitrate-N concentration than plants grown on the no N input treatments. Shoot ureide-N concentrations were not significantly different across N input treatments, which suggests that there were few differences in soybean root nodulation across soil N management treatments. Because larvae are thought to feed upon root nodules, it was surprising to find significant soil N input treatment effects on bean leaf beetle larval characteristics. Our research clearly shows that nitrogen inputs affected bean leaf beetle immature stages. However, the mechanisms that may be mediating these effects are not readily apparent.