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Weed control during the summer fallow

It’s mid-February, you’ve finally finished harvest and you’re thinking about how nice a few weeks of downtime will be before you start getting in to seeding, well don’t forget to manage your summer weeds!

 There are many reasons you might not want to let your paddock become an untamed green wilderness during the summer fallow, all of which will improve your chances of growing a bumper crop this coming season.

In drier areas of the country one of the biggest reasons to control weeds is to allow more water to accumulate in the soil, so it will be available to the following crop. This water is often stored deeper in the soil profile meaning the plant can use the water later in the season to maintain grain number and yield.

However, in the high rainfall zone where adequate moisture is not as much of a concern, the value of this extra water is usually not as high.  In some cases, it may even lead to early waterlogging. But while growers in the HRZ may want to dry their soil profile out to delay waterlogging, weed management is still an important factor to consider and letting them take over can have other negative effects on the following crop.

Weeds can use up valuable nitrogen and other nutrients in the soil. Having plant available nitrogen available in the soil at sowing can lead to increased yields, while reducing the amount of fertiliser inputs required during the season.

Controlling weeds over summer can also decrease the pest and disease burden in the following crop due to removal of the ‘green bridge’. Diseases such as rusts can live on volunteer cereals and some weeds if they are present over summer. Making the potential of pest and disease outbreaks more likely in the crop next season. Weeds can also cause interference or blockages with machinery at sowing, which can impact sowing depth, sowing consistency and crop growth rate at emergence.

There are a few factors to consider when deciding how and when to manage summer weeds. In very wet areas, weeds maybe helping by keeping the water table down to reduce salinity issues and nutrient leaching. In mixed farming systems some weeds such as windmill grass may be of value as livestock feed (but can be toxic) check out our weed fast facts booklet to see which weeds should be eaten over summer at https://sfs.org.au/project/less-weeds-better-pasture. If you do decide to spray, it’s important to make sure the weeds are actively growing and not under any stress as this makes them much harder to kill.

A successful crop starts before sowing, so make sure to think about summer weed management to give your crops the best season you can.

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