Hydroponic treatment with EPTC (S-ethyl dipropylthiocarbamate) inhibited leaf growth and stimulated stem growth of hybrid corn (Zea mays L. ‘Wisconsin 473′). Root treatment with GA3 (gibberellic acid) prevented leaf stunting from EPTC. Most abnormalities in foliar display and height from treatment with 50 μM EPTC were prevented by increasing GA3 levels from 0.5 μM to 10 μM over a week. The effect of EPTC on endogenous gibberellin activity was measured by bioassay of shoot extracts. EPTC (6.7 kg/ha) reduced the levels of total endogenous gibberellin-like substances in eight-day-old seedlings grown in treated soil. Under the environmental condtions of the experiment, this corresponded to the first discernable signs of injury. In addition EPTC induced an abnormal distribution of endogenous gibberellins in the shoots of older corn plants. Leaves of two-week-old EPTC-treated plants contained less gibberellin activity than the leaves of controls. Stems of herbicide-treated plants contained the same levels of gibberellin-like substances as the controls.
