THE EFFECTS OF MALEIC HYDRAZIDE ON GROWTH CONTROL OF PERENNIAL RYEGRASS (LOLIUM PERENNE L, CV. YARANDI)

Experiments were conducted in 1990 and 1991 to study the effects of maleic hydrazide (MH) on the vegetative growth reduction and decreased mowing maintenance requirements of perennial ryegrass (LoIium perenne cv. Yarandi). Treatments consisted of six rates (0, 1.2, 3.6, 6.0, 8.4 and 10.6 kg ha^-1) of Japanese maleic hydrazide (MH), OM-30 (6-hydroxy-3-(2H)-pydridazinone diethanolamine), with 30% active ingredient, and MH synthesized in Iran with the same formulation. Treated grasses were evaluated at ten-day intervals for growth reduction and on selected dates for color maintenance (chlorophyII content), as well as dry matter percentage in shoot fresh weight. Ten days after the first application of the growth retardant, 50% of the treated plots were treated again to evaluate the effects of double application of MH. No significant differences were found between the Japanese and Iranian MH formulations and consequently Iranian brand of MH may be recommended to replace the Japanese product. The majority of the treatments were effective in reducing vertical growth which lasted for 40 days after the first application. Abnormal yellow coloring of shoots was observed when MH was applied at the rates of 6.4 and 10.6 kg ha^-1 which ultimately resulted in complete destruction of the plots. The discoloration injury was proportional to growth suppression in terms of average height and increase in dry matter percentage in shoot fresh weight. Use of growth inhibitor from either source up to 6 kg ha^-1 may be reoommended. However, 3.6 kg ha^-1 MH is preferable because the green appearance of the grass may undesirably be changed.