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Overseeding: Winter growth, colour or both?

Many Turf Managers assume that turf-type perennial ryegrasses are all much the same, but the species Lolium perenne covers a wide range of genetic variation. One form of this variation concerns winter growth rate. Genetic types that originate from northern Europe (known as Continental types) shut down growth over winter in order to survive snow and ice. Almost all turf-type ryegrasses bred in the US are from Continental genetics, to suit their climate (even fairly warm climates like Virginia can experience polar vortexes, bringing snow and extreme cold).

But genetic types that originate from southern Europe, known as Mediterranean types, don’t need to shut down over winter – in fact they stay very active through the cold months. This has been exploited in Australian pastures for many years, and pasture-type ryegrasses bred in Australia and New Zealand are all based on highly winter-active Mediterranean genetics. The New Zealand bred turf-type ryegrasses are based on Mediterranean genetics too, and this is something that can be exploited on football grounds. Football is a winter game, after all. In turf plots at the PGG Wrightson research farm in Victoria, the Mediterranean cultivar Colosseum had a clipping yield up to four times higher than the Continental cultivar Fiesta4 during May and June (see Table 1). That’s an enormous difference, and growth at that time of the year pays a huge dividend in maintaining grass coverage and quality.

Of course, Fiesta4 is an extremely dark green, like all the US-bred Continental types. Mediterranean cultivars such as Colosseum are not as dark, more an ‘English green’ (see Photo 1). So you have a choice – select a US-bred Continental cultivar and enjoy the dark green colour, but miss out on some winter growth. Or select a NZ-bred Mediterranean cultivar, maximise the colour with nitrogen and iron, and benefit from the high winter growth rate when you need it most. Another alternative which has suited some venues, mix a Mediterranean cultivar with a Continental cultivar to get a good compromise.

Table 1: Fresh clipping weights (g/100m2/day) of perennial ryegrass cultivars, Winter 2011.

A bonus with the English green Mediterranean colour is that Poa isn’t so noticeable, as seen in the photo below.

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