Suppression of grass development by the growth retardant, mefluidide

Abstract

The effect of the plant growth retardant, mefluidide, on perennial ryegrass (Lolium perenne L.), prairie grass (Bromus cartharticus Varth.) and browntop (Agrostis tenuis Sibth) has been investigated. Early spring applications of 0.5 kg ha⁻¹ mefluidide effectively retarded vegetative growth for 8 weeks and dramatically suppressed the reproductive growth of all the grasses examined.

Physiological and morphological studies revealed that mefluidide acted primarily to reduce growth of the shoot, although minor retardation of root growth did occur. Analysis of growth parameters indicated that the reduced shoot growth was caused by reductions in tiller number, and sheath and lamina dimension. These factors subsequently resulted indecreased dry weight and leaf area of the plant. Thus, 0.5 kg ha⁻¹ mefluidide caused reductions of: 24% and 48% in tiller numbers, 45% and 22% in plant dry weight, and 63% and 36% in plant leaf area for perennial ryegrass and prairie grass respectively 6 weeks after mefluidide application. Prairie grass, unlike ryegrass, compensated for reduced tiller growth by increasing dry weight and leaf area per tiller. Plant height was reduced mainly due to inhibited sheath extension, although reduced lamina extension was a contributing factor.

Mefluidide reduced the proportion of grass in treated swards and caused the proportion of broadleaf weeds and dead material to increase. Tank-mixing MCPA plus dicamba with mefluidide gave good control of the broadleaf weeds but again increased the proportion of dead material in the sward. The experimental compound PP333 (formula undisclosed) gave better control of broadleaf weeds but did not retard vegetative grass growth as well as mefluidide. PP333 did not affect seedhead production.

Young perennial ryegrass plant absorbed and translocated considerable C¹⁴-mefluidide. In 48 h, 47% of applied mefluidide was taken up into the treated leaf and 7.5% translocated. Over this period, mefluidide was only slightly metabolised, with 93.4% of the extracted radioactivity identified as the parent molecule while the remainder consisted of two unidentified metabolites. The primary sites for accumulation of mefluidide were shoot components, principally lamina tissue. The translocation data suggested both phloem and xylem mobility. The lack of accumulation of mefluidide in the roots may relate to the lack of growth retardation of this tissue.