Effective weed management in the Riverina

After farming in the area for 23 years, it’s a fact that Simon Dal Broi knows all too well. Simon, his wife Sonya and their three boys, Samuel, Isaac and William, farm on 445 hectares near Griffith.

It’s predominately an irrigated cropping enterprise, but Simon also trades store lambs if the opportunity arises, grazing them before finishing them off in a feedlot. The entire property is arable and they make the most of it, something Simon believes is vital to their success. “We’re wall to wall cropping,” Simon said. “Land is too expensive around here to leave paddocks empty.”

For that reason, Simon grows both summer and winter crops, generally comprising of rice, wheat, corn, oats and faba beans. Rice has continued to be one of his main crops, taking 12 megalitres per hectare of water under flood irrigation to successfully grow the crop on the farm’s heavy soils, compared with 8 ML/ha required to grow corn.

Both the summer and winter crops are irrigated, but with water being the biggest challenge facing Simon, planning his rotation programs can prove extremely tricky. “Rice is a relatively easy crop to grow. Water is our main issue. It’s getting very expensive,” he said. “We can chop and change what we grow, so I’ve been concentrating more on my winter crops and only leaving out half as much land for summer crops. “We have to try and forward forecast what we’re going to grow in summer so we can leave the land out, but we don’t know what we’re going to get water wise. “We have to take a punt and guess what we’re going to get, so I’m just leaving 160 acres out for next year with the plan to grow some rice and corn. But we’ll see how much water we get.” With that in mind, Simon concentrates on the aspects of his cropping program that he can manage, such as weed control.

For the last 10 years, he has successfully grown rice crops free from burden weeds such as barnyard grass, dirty dora and starfruit – a factor he puts down to the quality of herbicides he uses and consultancy with his agronomist Mark Zanatta, Terra AG Services, Griffith. In a typical season to prepare for sowing rice, in October Simon will work his paddocks and apply 250 kilograms per hectare of urea and 250 kg/ha of starter fertiliser five or six days before irrigation commences.

The paddock is then rolled using a 12-tonne rice roller, creating ridges to prevent wind-blow of seed. Irrigation bays are stepped at 12 cm intervals to aid efficient water management. Seed is then broadcast using a spreader, before the bays are filled with water and attention then turns to weed control.

“I’ll speak with my agronomist, but usually within the first 10 days we go in with Taipan® herbicide at 2 L/ha and Ordram® at up to 3 L/ha, applied using aerial spraying,” Simon said. “Taipan works really well if you get water on within 10 days after application, then we lock it up for as long as possible – usually three or four days. “When the crop reaches two-leaf stage, we aerial spray Saturn® EC herbicide at 3 L/ha.”

Taipan is a Group H herbicide that offers an alternative means to control broadleaf weeds that have Group B herbicide resistance. Its active ingredient is benzofenap and, applied early, it has excellent crop safety, but it can also be used at later timings as it has no plantback restrictions.

Saturn is a Group J herbicide based on the active ingredient thiobencarb and is used to control barnyard grass and certain annual sedges, such as dirty dora. “Between those two herbicides (Taipan and Saturn), we’ve got good protection against barnyard grass, dirty dora and starfruit, which are some of our main problem weeds,” Simon said.“I really think Taipan, in particular, has been one of the best chemicals ever released for rice. “I’ve been using that and Saturn for the last 10 years and I’ve never really had a dirty crop. They’re really valuable chemicals in our production and very simple to use.”

Simon maintains a low water level in his rice bays for the first two or three weeks until the crop is established, then the bays are topped up. From then on, the crop is relatively low-maintenance apart from checking water levels and applying fertiliser in December, with another 125 kg/ha of urea applied by the end of the season.

The crop is harvested in March/April and Simon usually achieves yields of 12 tonnes per hectare. Once harvested, the paddock will be rested to grow rice again the following season, or mulched, burned and sown with wheat or another winter crop. “Because growing rice uses so much water, we use that residual moisture to grow a winter crop,” Simon said. “If we’re growing wheat, we’ll direct drill after going in with 250 kg/ha of starter fertiliser followed by 300-400 kg/ha of urea, but we’ll still water the crop up to three times in order to get the big yields.”

While his future rotations can be difficult to predict, there’s no doubting Simon’s ability to make the most of the hand he’s dealt. “A lot has changed in the way we farm over the years, particularly the methods we use, and we have become much more efficient with our weed control,” Simon said. That’s in large part due to the quality of the chemicals we have access to.”