Seed yield response of four cocksfoot (Dactylis glomerata L.) cultivars following the application of stem-shortening plant growth regulators

The seed yield response of cocksfoot (Dactylis glomerata L.) to stem-shortening plant growth regulators (PGRs) chlormequat chloride (CCC) and trinexapac-ethyl (TE) applied during stem elongation were evaluated in eight field trials in Canterbury; five irrigated and three non-irrigated. Across all trials and treatments the average seed yield increase was 53% resulting in an extra 290 kg/ha. In irrigated trials, the average response to PGRs was 68%, resulting in an extra 380 kg/ha of seed, compared with an average 27% response in non-irrigated trials. A mixture of CCC + TE (either 750 + 100 or 1500 + 200 g active ingredient [ai]/ha), applied at Zadoks growth stage (GS) 32 or split between GS 32 and GS 37–39, provided the largest and most consistent seed yield response of 86%, an extra 450 kg/ha. Reduced lodging was a factor in one trial only. In all trials, reduced stem length was associated with increased seed yield even in the absence of lodging. Seed yields increased at 12.5 kg/ha for every cm reduction in stem length from 130 cm (untreated) to 76 cm. This research provides evidence that the use of PGRs will improve seed yields of cocksfoot and the response is economic with a three- and sevenfold return on the cost of PGR and its application for dryland and irrigated crops, respectively.