|dc.description.abstract||A field trial was set up in spring 1986 to study the effects of the two plant growth retardants amidochlor (N-(acetoamino)methyl-2-chloro-N-(2,6-diethylphenyl) and mefluidide (N(2,4-dimethyl-5-[[(trifluoromethyl) sulphonyl] amino] phenyl] acetimide) on the pasture species Lolium perelllle. Amidochlor was applied at rates of 0.8, 1.6, and 2.4 kg ai ha⁻¹ and mefluidide at 0.15, 0.30 and 0.45 kg ai ha⁻¹. The chemicals were applied at two stages of development, vegetative and at the commencement of reproductive growth (double ridges).
Growth was measured using the parameters fresh weight, dry weight, dry matter percentage, leaf length, pseudo-sheath length, tiller leaf production, and apical development. An apical development scale was established to measure the effects of amidochlor and mefluidide on apical development. It was established that reproductive development was inhibited via the constriction of the sheath on the apex, thus causing apical death of some tillers.
The chemicals were found to inhibit leaf extension and stem growth. In the first phase tillering was inhibited, while in the second phase increase tillering was initially inhibited. This phase of tillering occurred about 4-6 weeks after chemical application tillering was enhanced. Tillering appeared to be related to the reduction in reproductive development. Total production of perennial ryegrass, except for the vegetative application of amidochlor (0.8 and 1.6 kg ai ha⁻¹) was reduced. Fresh weight of the treated plots was 84.7 % of the control while the dry weight was 84.1 %. The dry matter percentage was unchanged at 99.4% of the control. The chemicals appeared to have similar modes of action although mefluidide caused similar retardation regardless of application timing, whereas the vegetative application of amidochlor was more inhibitory than the reproductive application.
Flowering was inhiqited. All of the main tillers studied in the control plot flowered but only 10.2% and 30.8% flowered for the inefluidide and amidochlor treatments respectively. Tillers which did not flower underwent senescence. This appeared to affect other aspects of growth such as leaf and pseudo-sheath extension. Pseudo-sheath length was almost totally inhibited in senescing tillers. Differences between tillering were not as distinct.
The study showed that amidochlor and mefluidide have the potential to improve pasture management. Improvement was associated with retardation of reproductive development, improved survival of small, vegetative tillers, resulting in an increase in vegetative growth.
Mefluidide and amidochlor are chemicals with a potential for improving pasture for grazing and silage and hay making. They both act by constricting the sheath and thus imposing pressure on the apex. This causes a delay in reproductive development or, in some cases, death of the reproductive apex. The result is pasture with an increased proportion of vegetative tillers, a feature important in pasture improvement. The retardation effect of the chemicals means that maximum herbage production is delayed by about six weeks in spring following September applications.||en