Thomas G. Chastain
Why is lodging important in grass seed crops? Under certain conditions, the tiller cannot support the weight of the developing inflorescence and seed. The tiller lodges or falls to the ground, especially when there are high levels of nitrogen fertilizer and soil moisture present (Fig. 1). Both conditions are common in Oregon’s commercial grass seed production fields in the spring.
Lodging during flowering restricts pollination and reduces fertilization of the crop (Fig. 2). Grass seed crop yield is reduced as a result of lodging in two ways: seed filling is reduced due to self-shading of the lodged crop and the number of seed produced is reduced by lodging.
Elongation of the tiller in spring in grass seed crops results from activity of the intercalary meristem found above each node (Fig. 3). Each internode in the tiller elongates independently and this growth is promoted by the plant hormone gibberellic acid (GA).
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. In other words, the tiller does not elongate to the same extent when treated at the proper time with these PGRs. The PGRs are structurally similar to 2-oxoglutaric acid, a cofactor in the hydroxylation reaction. Palisade is registered for use in perennial ryegrass, tall fescue, and fine-leaf fescues. Apogee is registered for all grass seed crops grown for seed.
One interesting observations is that the seed yield enhancing benefit of these PGRs is not realized without the application of spring nitrogen on the grass seed crops. PGR-induced seed yield increases are most pronounced in the first year of the stand, but economic yield increases are common throughout the life of the stand. The best application timing begins after stem elongation has begun (BBCH 30-32) in the spring.
In addition to increasing seed yield of grass seed crops, several other effects have been noted. Reductions in tiller height, leaf length, spike length and in vegetative crop biomass are usual effects of application of these PGRs. No effects on numbers of tillers or root production, or on the number of spikes or panicles have been observed. Several yield components are increased by Palisade and Apogee including the number of florets and the number of seeds.