TIPS for the prevention and control of summer weeds were part of a Grains Research and Development-funded workshop at Dalwallinu last week, as well as sessions for local farmers to identify different weed species in their crops.
There was a particular focus on summer weeds as some herbicides are ineffective on certain species.
"Occasionally it matters what species the weed is, as sometimes the herbicide is not going to kill them all, so it's good to get out of the ute and have a look at what's there," said Department of Primary Industries and Regional Development (DPIRD) grains research and development officer Catherine Borger.
She said the My PestGuide Reporter app could be used as a helpful tool in identifying weeds in crops.
"You send a photo and some information on the weed and the botanists in South Perth will identify it," Dr Borger said.
Timing is also important in controlling summer weeds, as young, unstressed plants are easier to kill.
"However, most require a double knock, because it's just not possible to spray the entire farm when weeds are at the right growth stage, in ideal climatic conditions.
"Spray coverage is important, as small, stressed weeds are protected by stubble and this affects the performance of the herbicides."
Dr Borger said if spraying in hot conditions then use higher water rates and bigger droplets if possible.
With grazing becoming more common as a non-chemical route for weed control she said it wasn't a very effective method.
"It doesn't really matter how far you graze some weeds down, the plants will still set seed and it will be enough to carry them through to the next year," Dr Borger said.
"Button grass for example, at only 1.5cm tall will still produce 50 to 100 seeds per head, so that's 1000 seeds per metre squared."
If stock are in poor condition, they could also have some toxicity issues in consuming summer weeds.
Instead, the non-chemical option of a soil amelioration program was recommended as a second knock on crops, as long as the summer weeds had not set seed.
"Soil inversion can be a great second knock, but if your summer weeds have already set seed and you use a soil renovation, you're just going to bury those seeds, and you'll create a long lasting dormant seed bank in which they'll keep coming up over the next five years," Dr Borger said.
"A full inversion (mouldboard plough) can be really effective in getting rid of weed seeds, but you need to leave them down there at least 10 years, and even 10 years is a soft number, as it's not always guaranteed to get rid of some weed seeds."
In a summer weed survey conducted by DPIRD from 2015-2017, results showed African lovegrass, windmill grass, fleabane and wild radish led the pack as the most common weeds in the Wheatbelt.
Dr Borger said a lot of the most common summer weeds were also winter weeds, like wild radish and wild oats.
However, in less than 10 per cent of sites did the survey find the same summer weed repeatedly.
"Most of the time the summer weeds we looked at missed a year or so, which surprised us a bit," Dr Borger said.
"Winter weeds are a lot more predictable, for example if there is ryegrass and you don't control it, it's a pretty safe bet you're going to get ryegrass the following year."
DPIRD also conducted an experiment, planting a number of summer weed species and irrigating them to see when they would come up.
"We found that none of the summer weeds were actually restricted to summer," Dr Borger said.
"With sufficient water, caltrop usually came up in November, while Afghan Melon was usually a bit earlier in October, and that's something we see out in the field fairly often."
Dr Borger said the summer weeds coming up in spring posed a logistical problem, as they couldn't be out spraying while harvesting.
With summer weeds more variable than winter weeds, they were usually dependent on the conditions around germination.
"What weeds come up in summer really depends on what the temperature is when they're germinating," Dr Borger said.
"For example, if you have 12-24 hours of cold weather and rain then you will get a lot more wild radish than if you're getting a quick rainfall event with high temperatures."
Caltrop was recognised as a major problem for farmers, costing them $31 million per year and covering 1.6m hectares of farming land nationally.
The weed can reduce the yield of the subsequent winter crop by up to 40pc, as well as reduce grain protein and increase screenings.
"The seeds are also really prickly so livestock don't like them either," Dr Borger said.
With glyphosate and 2,4-D commonly used for summer weed management, there have been trials in recent years to identify other management techniques.
Dr Borger said two years of control in pasture, while leaving the caltrop seed on the surface of the soil, could help control the population.
If burial is a deliberate part of management, she said the seed needed to remain buried for at least 10 years.
"We really need a lot more work on caltrop management options," Dr Borger said.
