Thomas G. Chastain
There are two lodging control agents (plant growth regulators) available for grass seed producers in Oregon. Palisade (trinexapac-ethyl) and Apogee (prohexadione-calcium) plant growth regulators (PGRs) are acylcyclohexanedione inhibitors of the 3-β hydroxylation of GA. The known effects of the acylcyclohexanedione PGRs currently in use on grass seed crops are as follows:
- Increased seed yield
- Increases number of florets produced
- Increased number of seeds produced
- Reduced crop height and lodging
- Reduced leaf length
- Reduced vegetative biomass
- Increased harvest index
There have been no effects of the PGRs on the following plant characteristics in grass seed crops:
- Numbers of tillers produced
- Root biomass produced
- Spike or panicle production
- Spikelet production
However, there have been mixed and inconsistent effects of the two PGRs on seed weight. The attached table outlines 30 site years of data representing work in four species where seed weight was one of the characteristics examined (Table 1). Multiple rates, timings, and/or locations were a part of the studies. There were no trends in seed weight evident among the various species tested with regard to PGR application.
Statistically significant effects on seed weight were observed in 7 of the 30 (23%) site years. Five of the significant responses showed that PGRs increased seed weight while the remaining two had PGRs reducing seed weight. The increases or decreases in seed weight were small and results from seed germination studies indicate that there is no evidence that seed quality is affected by these small and inconsistent effects on seed weight. In the other 23 site years, PGRs had no statistically meaningful effect. While there are numerical differences that can be observed in this non-significant (NS) data, those difference are thought to be the result of chance and are evidence of the natural variation in the seed weight characteristic unrelated to the PGR management.
PGR applications at labeled use rates might in a few instances result in small increases or decreases in the weight of harvested seed in perennial grass seed crops. But for the majority of PGR applications, no effects on seed weight will be evident.
Table 1. PGR treatment effects on seed weight (mg) of cool-season perennial grass seed crops.
| PGR | Study | Species | Year | No PGR | PGR | |
| Palisade | Silberstein et al. | Perennial ryegrass | 1999 | 1.98 | 2.00 | NS |
| 2000 | 1.93 | 1.95 | NS | |||
| 2001 | 1.99 | 1.93 | NS | |||
| 2002 | 1.57 | 1.62 | * | |||
| Tall fescue | 1999 | 2.30 | 2.29 | NS | ||
| 2000 | 2.37 | 2.39 | NS | |||
| 2001 | 2.59 | 2.47 | NS | |||
| Creeping red fescue | 1999 | 1.09 | 1.14 | * | ||
| 2000 | 1.06 | 1.04 | NS | |||
| 2001 | 1.08 | 1.07 | NS | |||
| Chewings fescue | 1999 | 1.00 | 1.04 | NS | ||
| 2000 | 0.98 | 0.99 | NS | |||
| 2001 | 1.11 | 1.09 | NS | |||
| Rolston et al. | Perennial ryegrass | 2009 | 2.86 | 2.79 | NS | |
| Chastain et al. | Perennial ryegrass | 2002 | 2.01 | 2.05 | * | |
| 2003 | 1.96 | 1.90 | * | |||
| Zapiola et al. | Creeping red fescue | 2003 | 1.26 | 1.29 | * | |
| 2004 | 1.22 | 1.24 | * | |||
| Apogee | Silberstein et al. | Perennial ryegrass | 1999 | 1.98 | 1.97 | NS |
| 2000 | 1.93 | 1.92 | NS | |||
| 2001 | 1.96 | 1.91 | * | |||
| Tall fescue | 1999 | 2.30 | 2.30 | NS | ||
| 2000 | 2.37 | 2.44 | NS | |||
| 2001 | 2.66 | 2.52 | NS | |||
| Creeping red fescue | 1999 | 1.09 | 1.11 | NS | ||
| 2000 | 1.06 | 1.03 | NS | |||
| 2001 | 1.08 | 1.06 | NS | |||
| Chewings fescue | 1999 | 1.00 | 1.02 | NS | ||
| 2000 | 0.98 | 0.97 | NS | |||
| 2001 | 1.11 | 1.08 | NS |
