Source: P. Thomison, OSU
Ear pinching results from a reduction in number of kernel rows from the butt to the tip of the ear. Kernel row numbers may decrease by half (for example – from 16 to 7 to 8 kernel rows/ear). Ear length is usually normal.
Severe stress during the 7 to 10 leaf collar stages (V7-10) may result in reduced numbers of kernel rows. During normal growth and development of corn, the number of kernel rows doubles at about the V9 stage producing ears with even number of kernel rows. Late off-label broadcast applications of ALS/sulfonylurea herbicides where most of the corn leaves and whorl intercept the herbicide can disrupt this doubling resulting in the pinching symptom. Pinching symptoms have also been attributed to interactions of sulfonylurea herbicides and organophoshate soil insecticides.
Avoid postemergence broadcast applications of ALS/sulfonylurea herbicides after corn has reached the six-leaf collar stage (V6) and application of these herbicides with orgnophosphate insecticides.
Department of Botany and Plant Pathology. Purdue University 2013 Herbicide injury symptoms on corn and soybeans. Available at http://www.btny.purdue.edu/extension/weeds/herbinj2/injuryherb1.html [URL verified 3/28/2019].
Roozeboom, K.L., D. Ruiz Diaz, D. J. Jardine, R. J.Whitworth, and C. R. Thompson 2013. Diagnosing corn production problems in Kansas. Kansas State Univ. Agric. Expt. Stn. and Coop. Ext. Ser. Available at http://www.bookstore.ksre.ksu.edu/pubs/s54.pdf [URL verified 3/28/2019].
Strachan, S.D. 2004. Corn Grain Yield in Relation to Stress During Ear Development. Crop Insights Vol. 14, no. 1. Pioneer Hi-Bred, Johnston, IA. Available at https://www.pioneer.com/us/agronomy/ear_development.html [URL verified 8/26/2019].