Seed yield response of perennial ryegrass to low rates of paclobutrazol

Lodging of perennial ryegrass (Lolium perenne L.) seed crop is a widespread problem. Crop lodging reduces seed yield and interferes with seed harvest, This study was conducted to determine if low rates of paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-pentan-3-ol] influences seed yield and yield components of perennial ryegrass cv. Pennfine. Paclobutrazol was applied at either spikelet initiation or floret initiation at 0, 0.50, or 0.75 kg a.i. ha(-1). Paclobutrazol delayed the onset and reduced the severity of lodging. Averaged over the application timings, the 0.5 and 0.75 kg ha(-1) rates increased seed yield by 87 and 114% in 1983, respectively, and by 56 and 75% in 1984, No difference was observed between application timings in 1983, but in 1984 paclobutrazol had a greater effect in reducing lodging and increasing seed yield when applied at spikelet initiation rather than at floret initiation. Increases in seed yield were associated primarily with improvements in the number of seed set per spike, although paclobutrazol applied at spikelet initiation in 1983 also increased the number of spikes at maturity. Paclobutrazol did not affect straw weight, but increased harvest index in both years. Paclobutrazol, however, slightly reduced seed weight. We concluded that under western Oregon conditions, paclobutrazol rate as low as 0.5 kg a.i ha(-1) applied at spikelet initiation can significantly reduce lodging and increase perennial ryegrass seed yield, although rates greater than 0.75 kg a.i, ha(-1) may be required to achieve maximum yield.