Monolith root sampling elucidates Western Corn Rootworm larval feeding injury in maize

Authors: Riedell, Walter; Osborne, Shannon

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2017
Publication Date: 10/13/2017
Citation: Riedell, W.E., Osborne, S.L. 2017. Monolith root sampling elucidates Western Corn Rootworm larval feeding injury in maize. Crop Science. 57:3170-3178. https://doi:10.2135/cropsci12017.04.0218.
DOI: https://doi.org/10.2135/cropsci2017.04.0218

Interpretive Summary: Corn rootworms are tough and persistent pests of corn. Over time, these insects developed resistance to insecticides targeted to larvae and adults, adapted to annual maize-soybean rotation, invaded Europe, and developed resistance to toxic Bt proteins present in GMO maize. Greater understanding of the effects of these insect on corn root systems may aid in continued development of robust population management strategies against this important pest complex. We used a soil/root system monolith sampling technique that accurately measures root distribution in the soil profile without causing excessive damage to experimental field plots. This monolith sampling procedure allowed us to evaluate of root system distribution in the soil profile after larval feeding injury. Special software was used to develop contour plots of root length density measurements taken from the monoliths. These plots revealed dramatic as well as subtle differences in root distribution caused by larval infestation treatments. The dramatic responses were evident in the root mass at the plant base while subtle responses were observed in more peripheral regions of the monolith. We concluded that the monolith sampling procedure allows characterization of larval feeding injury on maize root distribution in the soil profile.

Technical Abstract: Monolith soil/root sampling techniques may help quantify maize (Zea mays L.) root system characteristics after western corn rootworm (Diabrotica virgifera virgifera LeConte) larval feeding injury. This 2-yr field study evaluated larval injury to maize root systems under controlled corn rootworm infestation (5850 eggs m-1 of row). Root damage ratings and root dry weight were measured in a 20-cm diameter root ball that was removed from the soil using standard “potato-fork” excavation techniques. The monolith sampler was used to remove 40 cm long by 5 cm wide by 30 cm deep soil slabs that were subsequently grid–sampled. Roots were separated from grid samples by elutriation and root length measured with the line-intersect method. Total root length monolith-1 was calculated and the distribution of root length density in the monoliths was visualized using contour plots. Larval feeding destroyed slightly less than one full whorl of adventitious roots and reduced root dry weight by about 21%. Total length of root present in soil monoliths was reduced about 26% by larval feeding. Contour plots of grid-sampled monoliths revealed dramatic feeding injury reductions in root length density in the portion of the root system closest to the plant stem. Data obtained from the 20-cm diameter root ball support the contention that the monolith technique provided quantitative estimates of root length density changes to the adventitious root system near the plant stem in response to larval feeding injury.