RESPONSE OF SPRING WHEAT TO THE APPLICATION OF 2,4-D AT VARIOUS GROWTH STAGES*

Summary. Two Triticum aestivum and two T. durum varieties were sprayed at five different growth stages with 0–5 and 1 kg/ha 2,4-D on the same day. The most sensitive stage was that of spike initiation, the most resistant phase followed the completion of spike differentiation, and plants close to caring were again very sensitive. Grain yield reductions of up to 19% with the low dose and 34% with the high dose were observed. The yield reductions at all growth stages were mainly due to a decrease in the number of kernels per spikelet. Application of 2,4-D during tillering also reduced the numbers of spikes per plant and spikelets per spike. Malformations of the spikes occurred in some plants of T. aestivum treated at spike initiation, but these spikes did not differ in grain yield from normal spikes from equally treated plants.