Annual rye-grass (Lolium rigidum) costs grain growers an estimated $93 million each year through yield losses and control expenses.
Its competitiveness, prolific seed production and widespread herbicide resistance have made it the most problematic weed in Australian grain production.
Researchers at the La Trobe Institute for Sustainable Agriculture and Food (LISAF) and the School of Agriculture, Biomedicine and Environment (SABE) examined how herbicide-resistant and herbicide-susceptible rye-grass populations responded to varying soil moisture levels under controlled glasshouse conditions.
The study found that moderate water limitation did not simply suppress rye-grass growth.
In some cases it stimulated development, with the resistant population producing up to 132 per cent more leaves and 153 per cent more tillers compared with saturated conditions.
Even under severe drought, which reduced plant height, root and shoot biomass, and seed production by up to 50 per cent, plants were still able to survive and reproduce.
The rye-grass also demonstrated greater flexibility in flowering time and maintained higher leaf water content under stress, suggesting it may be better equipped to persist in water-limited environments.
The research, published in the journal Scientific Reports, was led by weed science and agronomy senior lecturer Dr Ali Bajwa.
“Annual rye-grass is already one of the most difficult weeds for Australian grain growers to control, and our study shows it has a strong capacity to adjust to moisture stress,” Dr Bajwa said.
“The fact that the resistant populations can grow more vigorously under moderate drought and still produce seed under severe stress means growers need management strategies that are tailored to local weed populations and seasonal conditions.
“Resistant population did not show any major fitness cost and in fact, performed better under stress, which could be a double whammy for grain growers who are having to deal with herbicide resistant plants that are also drought hardy.
”Understanding how different rye-grass populations respond to drought can help growers and advisers design more targeted strategies to reduce seedbank build-up and limit the spread of difficult-to-control populations.
“We need further research on greater number of populations under field conditions in order to future proof our weed management programs in grain production in the wake of seasonal variabilities and changing climate.”
