Effects of the application rate and time of the growth regulator trinexapac-ethyl in seed crops of Lolium perenne L. in relation to spring nitrogen rate

Abstract

To test the effects of the growth regulator trinexapac-ethyl (Moddus 250 EC) in the main seed crop of grasses in the Netherlands, 10 field trials were conducted in perennial ryegrass ( Lolium perenne L.). These field trials were carried out in first and second seed harvest crops during 1999–2002. Four rates of Moddus (untreated, 0.4, 0.8 and 1.6 L product ha −1) were applied at the start of stem elongation (DC 30–31, zero to one node) during the first two years. In addition, the effect of timing of the application of 0.8 L Moddus ha −1 was studied (untreated, DC30–31, DC31–33, DC33–37). In most trials, in addition to the normal amount, 45 kg N ha −1 extra spring nitrogen was applied. The work reported is valuable, and has relevance to all areas of the globe where this perennial ryegrass is grown for seed, e.g., northern Europe, the US (particularly, Oregon), New Zealand, Australia, Chile and Argentina. Crop development in spring was partly affected by weather conditions during the previous autumn and winter, so while Moddus was applied at the same crop development stage, the calendar dates varied for the different harvest years. Temperature sum from 1 November accounted for only 51.4% of the variation. Applications at higher rates increased the reduction of stem length, lodging of the crop and the density of panicles. Application later than DC30–31 resulted in shorter culm length and higher total dry matter weight of the crop. The application of the highest rate of Moddus (1.6 L ha −1) at the crop development stage DC30–31 never resulted in an unacceptable final phytotoxic effect. Effect of Moddus on seed yields was inconsistent; the potential seed yield increase was about 10%. In general, there was no significant interaction between the application of 0.8 L Moddus ha −1 at the crop development stage DC30–31 and the spring nitrogen rate. The results show that DC31–33 is the best time to apply 0.8 L Moddus ha −1. In second seed harvest crops of lawn types applying 0.8 L Moddus ha −1 together with increasing the amount of spring nitrogen can be considered.