Too high levels of herbicides in certain soil strata can lead to changes in root development. These have an inhibited growth which gives the locally concerned portion of the stem a very particular appearance: swollen, bumpy, sometimes grooved and superficially corky. Numerous outlines of roots stopped in their development are also visible. These sketches largely explain the spectacular aspect of this symptom.

Several herbicides are known to cause such deformations of the taproot and of the buried part of the stem: pendimethalin (figure 1), trifluralin More information on the phytotoxicities ( chemical injuries ) is given in the sections relating to anomalies of growth and coloring of the leaves.