Studies on the influence of some auxin herbicides on grass-seed crops

Applications of 2,4-D or MCPA may cause malformations in the initiated leaves of both grasses and cereals, during vegetative stages of development. 2,4,5-TP also caused malformations in stems and leaves, but only after the plants started to shoot. By their strong tillering the reaction of grasses to auxin herbicides was more complicated than that of cereals. The spraying effect was assessed primarily by the number of sprouts influenced in the harvested haulms. When the grasses were most susceptible varied, probably through differences in tillering during cold weather and a different number of sprouts developing after treatment, thus causing a difference in the percentage of sprouts affected, and through differences in photoperiod for ear initiation. All grasses studied required different periods of cold or short days to reach the stage of ear initiation. The moment of ear initiation, varying between species, corresponded with the end of the susceptible period of the vegetative parts and was usually correlated with the severity of leaf abnormalities. The susceptibility of inflorescences to MCPA and 2,4-D was closely related to that of the leaves. 2,4,5,-TP disturbed the structure of the inflorescences mostly later during shooting. Application of all the chemicals to grasses after forming 3-4 tillers in autumn did not decrease seed yield. But application after winter may do so. The germination decreased only after application during late developmental stages of the inflorescence.