Battling barley grass a key to good winter crops

Because these crops are commonly sown on the first autumn rain, or late summer rain, or are sown dry to establish on these early rains, no opportunities exist to achieve a good weed kill before sowing or/and establishment.

As with most successful weed control programs a combination of control strategies generally is required to control weeds such as barley grass in early sown crops. Herbicides are only one part of the control strategy.

For many situations a good starting point is late winter-early spring, coming from a pasture phase to a cropping one. Ensuring no weeds such as barley grass (early flowering and seed setting) are allowed to set seed helps ensure a relatively low soil weed seed bank for such species. Timely spaying out with glyphosate herbicides while still actively growing and early flowering can result in a very effective kill.

Early autumn (and in cooler environments late summer) sowing can result in winter cereals getting well established before barley grass germinates. For example, in our area, the northern part of the central west, we have been able to sow late February (only when forecasts are for mild following weather) to mid-March in all of the past eight years with the exception of one year, when plague locust populations were high.

Being able to reliably sow early is helped if using lighter soils (where this option is available), where sub soil moisture has been captured in the fallow, where stubble cover is maintained, and if minimal soil disturbance combined with press wheels are used. As a guide we sow when mean soil temperature is about 23 degrees Celsius or lower.   

Competitive crops also help compete against weeds. Factors to consider include vigorous varieties, relatively closer rows (for example 20cm versus 30cm, far more competitive), use bigger seeds with high germination, sow not too deep (4-5 centimetres for cereals) and ensure high soil fertility. Where appropriate disease control, for example rust in early sown oats, also helps improve crop competitiveness against weeds.

Herbicides can help suppress barley grass and vulpia (and other weeds such as ryegrass and brome grass) but commonly are not good enough to be termed “a simple, effective” control measure. Oats has few herbicide registered control options. 

Chlorsulfuron is registered for barley grass at the two-leaf stage onwards. Effectiveness depends on factors such as following light to moderate rain events soon after application). For wheat barley and triticale there are preemergent as well as more post emergent options for most annual grass weeds such as barley grass. Be especially aware of herbicide resistance issues for many of these products.

Grazing out a winter fodder crop such as oats with a spray-out as weeds like barley grass begin to flower is an increasingly viable option. Early sown cereals can provide 120 to 150 days grazing at 25 dry sheep equivalents/ha over the grazing period with gross returns well over $1000/ha. Growing costs of about $350/ha can still ensure reasonable to good profits, plus a great weed control outcome.

Using grazing brassicas such as canola, including winter habit types, also provides opportunities to use grass-effective herbicides. Increasingly we will see glyphosate resistant varieties that allow glyphosate as part of the herbicide in-crop choice. Careful use of these herbicides remains critical to avoid herbicide weed resistance. 

Next week. NSW Grasslands conference to feature success with new legumes.