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.  But will that be the case in spring 2013?

The winter months of January through March 2013 have been the 2nd driest winter period on record at Corvallis with only 6.28 inches recorded.  Can we expect more of the same dry weather during spring?  No one can say for sure, but an examination of weather records for the past 124 years reveals that when precipitation is very low (50% or less of the 16.02 inch normal) in January through March, the following April through June period averages 5.78 inches or near normal rainfall (normal is 5.83 inches). 

Despite the very dry weather that has been recorded to date, there may still be enough rainfall present in coming months to make lodging a problem for local seed growers.

Figure 1. Lodging in ryegrass. (T.G Chastain photo)

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.

Figure 2. Lodged tiller. (Illustration by T.G. Chastain)

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).

Figure 3. Elongation of grass tillers and development of the inflorescence in spring. (Illustration by T.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. 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 seed yield increases are common throughout the life of the stand. The best application timing begins after stem elongation has begun (BBCH scale 30-32) in the spring.

A final observation regarding spring weather conditions and PGR use in grass seed crops, our research has shown that seed yield is increased in perennial ryegrass even in low rainfall springs with the reduced lodging that accompanies these periods.

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