Ethephon as a Morphological Regulator for Corn

Ethephon (2‐chloroethyl phosphonic acid) has been used to reduce ear height in order to improve lodging resistance of corn ( Zea mays L.). However, untimely applications may reduce area of photosynthetically important ear leaves. Thus our objective was to determine the range of plant development stages over which ear height reduction could be achieved without advesrsely affecting ear leaf area. Two corn hybrids were space planted in the field in 1986 and 1987, and treated with ethephon at 284 g ha −1 over a range of vegetative growth stages. Ear heights were most reduced by ethephon applications from V9.2 to V10.6 in 1986 and at V13.0 in 1987. Individual internodes most influenced by ethephon were those actively elongating at the time of application. The area of the three ear leaves was most sensitive to treatments from V5.3 to V9.2 in 1986 and V6.0 to V8.8 in 1987. Early (V3.7 to V4.3) or late (V13.4 to V16.8) vegetative—stage application did not reduce grain yield per plant, while those treatments that most influenced area of ear leaves had a similar negative effect on grain yield. For the hybrids studied, the growth stages for which applications produced the best combination of ear height, ear leaf area, and grain yield were from V10 to V13, corresponding to developing tassel lengths of 30 to 300 mm. When ethephon rates were expressed as mg g −1 dry weight, more of variation in ear height, leaf area, and grain yield was explained than when rate was expressed as mg ethephon per plant. This implied that some growth regulator effects referred to as “timing” influences may be better explained as “dosage” effects. Additional research under higher planting rates will be necessary to validate these results.