Yellow Bristle Grass Management

Yellow bristle grass (YBG) is a summer-growing annual weed. It is unproductive later in summer, very persistent and difficult to get 100% control of, and it can spread very rapidly.

Alan Henderson, a dairy farmer who has been a FAR board member for the past 12 months, is an enthusiastic advocate for research into this pervasive weed. “The driver for this research is knowledge and the opportunity to be at the forefront of developing research and to see how we will implement it in our own farming operation.” 

Alan has a 180ha dairy farm milking 650 cows, a commercial calf rearing unit and is also growing 80ha of maize. There’s also a nashi, kiwifruit and apple orchard, which is leased out.

Alan says “About 20 years ago we had some paddocks that were very unproductive in the later part of summer, and we didn’t know what it was. So it’s been around a long time. Only in the last five to eight years has it been identified and resources put towards a managed eradication programme. More recently there’s been research into how to manage the seed bank, when it germinates and how to restrict the spread of the seeds.

Now we have 40% of our 300ha infested with YBG. Of that area, we have regrassed 80% in the last five to six years as a way to control it. This is the best method of controlling it until the researchers find a spray to control or eradicate it. There is a selective herbicide from Bayer called Puma S which can now be used to help, and should be used after germination but before seeding.

I would estimate YBG has cost us up to 20% loss in pasture production on our milking platform of 180ha. The only way we have maintained production with the lower pasture growth is by increasing the levels of bought feed. We use maize silage or palm kernel or off-farm grazing. We also do a lot of summer cropping now. 

One of the problems is you can’t make hay with the grass, as the seeds don’t die, so you have to turn it into silage. That’s one way of reducing the seed bank. Every year we make 80 bales of silage. AgResearch is doing some research into finding out how long it takes the seeds to die in silage and they think there is no germination of seeds after only seven days.

I’ve been on the YBG research committee from the early stages. We have run trials on this farm in respect of chemical applications to see what can control it, and a couple of field days have been held here. FAR is doing some research in conjunction with other companies into how to eradicate YBG in maize.

It is spread along roadsides and can be found around marker pegs. There’s a bit of research into how roadside infestations can spread onto farms. 

Dr. Trevor James from AgResearch has been involved in the research programme. He says the study has highlighted three main messages :

• It is a real problem. Don’t ignore it. If you ignore it, it is at your peril. It affects pastures in two main ways. Cows avoid eating it, and it lowers feed quality. The cost of this has been calculated at $343/ha, which is the cost of supplementary feeding to maintain milk production at pre-infestation levels. The main way it gets to new farms is through imported feed, silage, or from roadside infestations. When it dies in autumn, the ryegrass is weaker, and it leaves gaps for winter weeds, which then compete even more strongly with the ryegrass.
• Dealing with Yellow Bristle Grass is not simple and a whole farm systems approach needs to be taken, using a variety of control methods. Spraying is a good tool and is effective but must be done early and it is difficult to get the timing right. Getting good control by spraying is proving more difficult than we first thought. Yellow Bristle Grass hasn’t become resistant to any herbicides yet, but if it does we are in deep trouble. The tricky thing is people recognise it when it goes to seed, but then it’s too late to control. The best time for control is before Christmas when it is more difficult to identify.
• As a weed of dairy pastures it is ranking up there with giant buttercup and Californian thistle, both of which are perennials. Yellow Bristle Grass is already throughout the North Island. It is not on every farm yet, but it is spreading at a rapid rate. In the Horizons Regional Council area it has been mapped on every roadside. Horizons are hoping to control it from Wanganui south to stop it getting into pastures. With the expansion of dairying into the South Island there are no climatic reasons why Yellow Bristle Grass could not become a major problem there.

The ute guide to Yellow Bristle Grass is available from DairyNZ. This is already on its third printing of 5000 guides.