Crop protection - In this test, nature will always win the toss
By Emma Leonard
Although the tagline on Dr Sally Peltzer’s email says “Make no mistake, the weeds will win. Nature bats last”, she and colleague Alex Douglas and collaborators at the WA Herbicide Resistance Initiative (WAHRI) are doing their utmost to beat nature.
“We now know two more key facts about the life cycle of annual ryegrass,” says the WA Agriculture Department’s Dr Peltzer.
“Firstly, 70 to 80 percent of annual ryegrass seeds germinate the year after seed-set, leaving 20 to 30 percent in the seed bank.
“Secondly, the majority of this germination occurs in the two months after opening rains.
“To maximise weed control, we either want to prevent germination or to stimulate as near to 100 percent of seeds to germinate in the first year, and then control the majority of the weed seedlings.”
Two years of research by Dr Peltzer at Katanning has shown that burying seed deeper than 10cm results in a dramatic reduction in germination of annual ryegrass (see graph below). Where soil was inverted using a modified mouldboard plough, fewer than 20 annual ryegrass plants/m2 were recorded, compared to about 550/m2 under the no-till treatment.
But before any devoted no-tillers despair, it is worth noting that the best results were achieved with one-year mouldboard ploughing followed by no-till with knife points.
“We expect that a full inversion every eight to 10 years may be sufficient to minimise annual ryegrass populations and would be especially helpful in managing large resistant populations,” says Dr Peltzer.
Deep burial is one solution, but shallow burial may be another. Dr Kathryn Steadman at WAHRI has discovered that when annual ryegrass seeds are stored in moist dark conditions (in the soil) they become more sensitive to light, and dormancy release can occur in two to three weeks for nearly 100 percent of the seed bank population.
In dry conditions, the dormancy release period is generally several months of high temperatures, but for about 20 to 30 percent of the seed bank this is still not enough to break dormancy in a single year.
The sticking point is that after two to three weeks’ shallow burial in moist soil, the seeds need to be brought back to the surface and exposed to light to stimulate germination.
Therefore, for the time being, deep burial together with current techniques to prevent seed-set is the more feasible option. But, in the future, more targeted germination control may be another weapon in the grower’s arsenal for managing annual ryegrass.
GRDC RESEARCH CODES DAW613 & UWA399, program 3
Region North, South, West