Feathertop Rhodes (FTR) grass is a major weed in broadacre cropping systems in Central Queensland, the Darling Downs and Western Downs regions of southern Queensland, and in northern New South Wales. FTR has proven very difficult to control.
Previously a weed of roadsides, fence lines and wasteland areas, FTR has now become an issue in cropping country, says Jock Leys – business development manager at Sumitomo.
“It is not overly susceptible to glyphosate herbicide, particularly after the early tillering stage. The prolonged use and reliance on glyphosate in the fallows of these cropping systems has assisted with a species shift towards this grass. For the same reason, FTR has also recently become an issue in glyphosate-tolerant cotton systems.”
Mr Leys said the most successful strategies employed by growers for managing FTR have included the use of residual herbicides. Either directly targeted at known FTR ‘problem’ paddocks, or more broadly, by keeping FTR at bay when targeting other grass weed problems on the farm.
The viability of most other grass weed seeds in the soil is longer than for FTR, so when growers are incorporating residual herbicides into their program to manage grass weeds such as awnless barnyard grass, FTR is often also controlled or suppressed.
A recent study published be the Northern Grower Alliance and GRDC examined the use of residual pre-emergent herbicides for the control of FTR.
Although FTR is generally considered a summer grass weed, emergences can be seen in winter. Field experience suggest that periods of soil wetness are more important than temperature for FTR germination and emergence.
Glasshouse studies by Queensland Department of Agriculture and Fisheries showed that FTR will emerge following as little as a 10mm simulated rainfall event, however larger rainfall events resulted in increased emergence. Awnless barnyard grass, common sowthistle and flaxleaf fleabane were also included in the same study.
The rainfall requirement for emergence of FTR was less than for awnless barnyard grass, especially at cooler temperatures (15–20C compared to 20–30C), while rainfall >20mm was required to provide significant emergence of common sowthistle and flaxleaf fleabane.
The ability of FTR to establish on lower rainfall highlights one of the reasons that FTR is often the first weed to establish following spring rainfall.
In this study, Dual Gold at 1 L/ha or Valor 210 g/ha were applied at the end of July and end of August as single applications to compare with the same timings ‘topped up’ with Dual Gold 1 L/ha at planting (sorghum).
Rainfall of 2mm was received in the week following both July and August applications. Both applications were compared to Dual Gold applied at planting.
Figure 1. Counts of FTR shortly after planting, highlighting the residual control
achieved from either Dual Gold or Valor applied at the end of July or August.
Figure 1 shows the counts of FTR shortly after planting and highlights the residual control achieved from either Dual Gold or Valor applied at the end of July or August. A commercial knockdown of glyphosate was applied at planting and the trial area also received an additional glyphosate application following the emergence count in Figure 1.
Mr Leys said this study clearly demonstrates that Valor provides excellent long-lasting control of FTR when applied late winter/early spring (Figure 2).
Figure 2. Counts of FTR approximately two weeks after planting.
Valor has residual registration in fallow and prior to planting cotton, sorghum, soybeans, mungbeans, peanuts, pigeon peas, navy beans, maize and sunflowers.
Mr Leys said Valor has short plant-back requirements prior to summer crops an provides 6–8 weeks residual control for late fallow and residual carryover/control into the emerged crop.
In addition to control of FTR, he said Valor can also provide residual control of a range of difficult to control broadleaf weeds such as flaxleaf fleabane, common sowthistle, red pigweed, caltrop, bladder ketmia and Ipomea species such as bell vine and morning glory.
