Dardanup Rural – Controlling barley grass this season
Article contributed by Bernie Zahra of Dardanup Rural.
For some time we have seen barley grass (Hordeum spp.) becoming an increasing problem in South West pastures. It is well adapted to survive and dominate our grazing areas when left un-managed
Barley grass has long been thought of as an annual grass that germinates rapidly after the first season breaking rains, i.e. a weed with low seed dormancy. This can potentially offer a the benefit of early feed for livestock.
More recent research however is challenging the low seed dormancy theory. Albeit from lower rainfall areas, work by DPIRD in WA has shown barley grass populations have developed a degree of seed dormancy with the potential for staggered germination, even as late as August. Our own observations support this is happening in South West WA.
This may be due to a shift in population dynamics and/or other factors such as an increase in non- wetting soils or later seed return to the soil which naturally delays germination.
Either way this needs to be considered when planning a control strategy using integrated weed management that includes early, mid and late season barley grass control.
Herbicide resistance also needs to be considered. Whilst not a common problem with barley grass at the moment, it is increasing in more intensive cropping regions.
Early season control is relatively well understood, essentially using knockdown (glyphosate or paraquat) herbicides to control the early germinating barley grass (at the 2-4 leaf stage) followed by seeding with ryegrass.
Alternatively, you can use animals to graze the barley grass out of the pasture. This is not always the most reliable option, however can work in a sacrifice paddock situation, after which seeding can take place.
Early season control relies on an early season break to give you the time to allow for a knockdown and still establish a strong pasture. Unfortunately it doesn’t happen that often, although this year has presented some great opportunities for this tactic.
2024 trials
Last season at Dardanup Rural we wanted to better understand mid season post-emergent options, in particular the herbicide Tramat® (a.i. ethofumesate).
Tramat is registered for post- emergent grass (barley grass and winter grass) and broad leaf weed control in ryegrass pastures. Tramat and other products containing ethofumesate have been registered and available for some time. However their use is not that well understood, mainly because in the past they have been cost prohibitive.
We looked at a farmer paddock that was sown dry to an annual ryegrass, clover and oat seed mix. The paddock had a history of barley grass so we expected a germination on the opening rain together with the sown pasture species. We applied Tramat at 3L/ha on May 16th with the annual ryegrass at 2-3 leaf stage, clover at 1-2 TFL and the oats at 3-4 leaf. The barley grass was at 4 leaf and winter grass was at 1 leaf or still emerging.
This herbicide is taken up by both plant roots and shoots. Hence, conditions at the time of application and spray coverage are both important to control existing weeds and achieve some residual control.
The herbicide gave excellent control of both barley and winter grass to the point where this season, we can clearly see barley grass germinating from seed that was returned to the soil in the untreated part of the trial.
The clover was taken out by the herbicide (as per the label), so do not include clover in seed mixes where the herbicide is part of the plan.
The oats also suffered an unacceptable level of damage.
Interestingly Dairy Australia has received a permit from the APVMA to use the herbicide Matrix® (same a.i. as Tramat) at 1.5L/ha post-sow pre-emergent, with or without a follow up 1.5L/ha application. This is a similar use pattern that we know is used in New Zealand and one we have also trialed locally. Matrix is manufactured by Adama and it is their research which has supported the permit.
Late control
Late season control centres around the use of chemical or mechanical options to stop grass seeds from becoming viable and returning to the soil. Using the correct chemical at the right time has proven to be very effective in managing barley grass seed set.
The downside of course is lost spring production, so this may be combined with sowing a spring/summer fodder option that can then be grazed and does not leave the soil exposed over summer.
Rotating away from ryegrass to prioritise grass weed control is another integrated weed management option. For example, a legume based pasture can provide many grass weed control options at a relatively lower cost.
Cereals such as oats also allow for different herbicide/mechanical weed control options.
