Weed control

Weed Competition Graph

After the recent rain, a lot of weed management is taking place throughout the industry.

Here in the wet tropics, weeds and vines grow rapidly with the ideal growing conditions. One definition of a weed is just a plant growing where you do not want it to, and this applied to the home garden as well as commercial crops.

A lot of time and resources have gone into developing different herbicides that work within a crop and these fall into two main categories: Pre and post emergent.

Pre-emergent herbicides are applied once planting is completed, but before the crop starts to grow. These herbicides do not stop weeds germinating, but once the weeds have germinated and broken through the soil surface they die off.  Pre-emergent herbicides commonly work for about 6 weeks after application.

Post emergent herbicides are used on established weeds within a crop. These include herbicides like 2,-D, which is a plant hormone that causes broadleaf weeds to grow too fast and die off.

Since the 1990s, all agricultural industries have taken various approaches to make sure anyone using herbicides knows the correct and safe way to use them in an environmentally friendly way. 

The industry went one-step further back in the late 1990s by developing a series of trials to illustrate the importance of timely weed control. These trials showed that if no pre-emergent was applied until 4 weeks after planting, there was a yield loss of around 15% of the crop from weeds competing for moisture and nutrients. If no weed control is carried out for 12 weeks after planting, almost 60% of the crop yield could be lost. Of course, the scenario of no weed control at all would be very rare but it shows just how important it is to use herbicides in a timely and safe way because they are essential to our modern agricultural systems.

Another key aspect of herbicide work these days is to develop information on how new cane varieties react to herbicide use. Due to cane, being a grass, it is possible for some “phyto-toxicity” or burning of the leaves to occur from some herbicides on some varieties.  To determine the risks of phytotoxicity, SRA carry out trials at Meringa station, south of Cairns, by applying various herbicides to many new varieties in a set area and observing the results over several weeks.

Closer to home, TCPSL and TSl are in the process of updating our local weed management guide, which will also include some local observations of any phyto-toxicity if it occurs.

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