WestVic Dairy News - February 2011 Edition
Seed heads – what to do about them
Michele Ryan, Dairy Extension Officer, Department of Primary Industries, Warrnambool.
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With higher summer rainfall than usual, it is proving a challenging time for managing pastures in the south west. In paddocks that have been harvested for hay, the rainfall and milder temperatures have enabled the perennial ryegrass to maintain production with good quality green feed with limited seed head development.
However, any paddocks that had been harvested early in the harvest season, and any paddocks that became rank and out of control during the spring period, are causing some headaches with seed head production.
So what are the options available to control these undesirables?
Using dry stock to follow the milkers is often a strategy that has been used with great success. You need to be careful however that the paddocks are not overgrazed – that is, grazed below 5cm, as this can set back the pasture for the next rotation. Making sure that there is adequate supplement available will help minimise damage to pastures by overgrazing.
Pre-grazing topping (topping pasture before cows graze) is usually recommended as a means of bringing pasture back under control when pasture growth rates have exceeded grazing pressure. Pre – grazing topping is only recommended in situations when pasture on offer is over 2800 kg DM/ha (an average visual height of 12 – 18 cm). This is really only a once off event to bring out of control pastures back into the grazing rotation, and should not be used as a regular management tool.
Wilt pre-grazing topped pastures for 12 to 24 hours before grazing as this generally improves utilisation of the pasture by reducing the cows' ability to selectively graze. It is important to note that when using this method it takes cows time to adapt to the change in the pasture and it may be quite a few days before they start to graze the paddocks well. Pre-topping really only works well if the paddocks are good quality dense pastures. It is generally a waste of time and tractor fuel to be topping poorer, weedier pastures or paddocks that contain a lot of dead and stemmy material. Cow intake may rise, this is because the cows have been “conned” into eating pasture they wouldn’t usually consume, and milk production may fall.
Post – grazing topping pastures (topping pastures after the cows come out) is generally seen as a last resort to clean up rank pastures. The principle behind post grazing topping is to remove developing seed heads and pasture residues that develop when cows are being overfed. This may occur either when pasture growth rates exceed the grazing pressure applied, or when high levels of supplements (relative to feed on offer) are being fed.
Post grazing topping should take place within 3 to 4 days from when cows first grazed the paddock; otherwise it will set back regrowth. The mower used for topping should be set to cut between 4 and 5 cm height from the ground. Only use mechanical topping when more than 25 to 30 per cent of the paddock is covered in clumps that you can not see the ground through, and if the cheaper option of grazing with dry stock is not available.
It is important to make sure that you avoid overgrazing, whatever option you chose to clean up the seed heads and help your perennial ryegrass along. Aim for a residual of 4 – 6 cm and aim to graze at 2 and half or 3 leaf stage to give your perennial ryegrass it’s best start to the year.
