To a city person such as I once was, raising cattle may seem to be quite easy. You put the cattle in the paddock and they eat the grass. Done and done. When it's time to sell, you get all the cattle out of the paddock and send them off to the meatworks. How easy is that? Sit back for drinks on the veranda for the rest of the year.
Actually, there is a lot more involved. I'll try to keep you updated along the way but for now let's talk about weeds. I look at a green field and think, "Gee that's a lot of grass" but actually it may not be the case. In fact, some grasses are even considered a weed.
Here's the rundown. Lovegrass is a weed that is difficult to selectively spray for. This is because it is a grass and therefore you can't just do a weed-n-feed type thing where you spray everything and the lovegrass gets got and nothing else. Another reason it is hard to spot in amongst the other grasses. It's germination cycle is very short, meaning that it grows from a new plant to an old plant with seeds quite quickly. The cattle will avoid it then and it spreads while the other grasses are being grazed. Other weeds such as creeping lantana grow in inaccessible places and are difficult to control because they are difficult to get to. Some weeds, such as mother-of-millions are toxic to cattle and will make them very sick if not kill them. Seeds can be spread in the wind, by birds, by vehicles and machinery or washed down creeks.
This all adds up to less grass in the paddock for our cows to eat so our graziers (farmers) need to do some serious management. This usually involves plenty of mathematics. They have to calculate the amount of palatable grass in a paddock and determine how many cattle can run in that paddock so that the grass can grow back before it all gets eaten. They have to determine the cost of doing some weeding versus the amount of extra cattle that can be put in that paddock. If you're at school and you think you don't need mathematics because you're going into agriculture, here's your wake-up call. Farmers and graziers do maths nearly every day.
So the next time you see a grassy paddock, it may not be the low-cost, low maintenance farm that you envision. It could require a lot more work than you think.
update 16/1/12 here's another devastating weed-grass http://www.gympietimes.com.au/story/2012/01/14/plague-of-grass-girant-rats-tail-weed/