Weighing up costs, benefits of weeds

Weighing up costs, benefits of weeds


Grains
UPS AND DOWNS: Southern Farming Systems warns that keeping weeds to help meet feed demands can come at a cost at the start and end of the season.

UPS AND DOWNS: Southern Farming Systems warns that keeping weeds to help meet feed demands can come at a cost at the start and end of the season.

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Weeds can provide a valuable feed source to help meet winter and summer stock feed demands, but generally incur a cost.

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Southern Farming Systems is testing the feed value of weeds to help farmers weigh up the costs and benefits of getting rid of them.

Researcher Bree Downes-Smith says: “Weeds can provide a valuable feed source to help meet winter and summer stock feed demands, but generally incur a cost in the farming system.”

Barley grass – an annual species which quickly germinates following the autumn break – is highly digestible, with a good metabolisable energy (ME) content of 11.9 MJ/kg DM and ample crude protein levels of 27 per cent, which meets lactating ewe and lamb requirements.

However, it comes at a cost at the start and end of the season. SFS’s Lisa Miller warns: “The seed heads can cause eye injuries in grazing stock and reduce wool quality. It competes against sub clover for space at the start of the season and finishes off earlier than perennial grasses leaving bare ground, opening up the pasture to further weed invasion or erosion.”

Growers generally utilise its grazing value in winter and look to reduce seed set in spring through spray topping or silage making.

“Spray topping is often not 100 per cent effective at stopping seed set and some seed may reinvade the following year,” Ms Miller said.

“This is why two years of control and a follow up like silage, is the best practice for removing weeds.” 

Ms Miller also warns if rain occurs in the days after spray topping with paraquat, it can stimulate the emergence of a new seed head. Winter cleaning using herbicides such as paraquat, and in some situations, Shogun, are useful methods to remove barley grass in good seasons when there is enough feed, as it generally suppresses pasture growth post spraying.

One weed that nobody should stress about removing from a feed production point of view is onion grass.

“Onion grass tested really poorly for digestibility and metabolisable energy, with an ME of 7.1 MJ/kg DM and Neutral Digestible Fibre was 60.2 per cent (winter tested),” Ms Miller said. 

“It’s like letting your sheep eat strips of synthetic grass.”

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