Harsh mallow hard to digest
GroundCover™ Issue: 49
By Eammon Conaghan
The nation’s weeds assault has taken another turn for the worse with the arrival of a small-flowered mallow (Malva parviflora) – and it brings with it a natural resistance to glyphosate herbicides.
You may not have heard of the small-flowered mallow because it is relatively new to these parts, but University of Western Australia researcher Professor Julie Plummer suspects it will soon be a household name.
“Small-flowered mallow can produce 5000 seeds per plant and the resultant progeny mature very quickly, which means populations can explode. Being capable of ‘in-breeding’ also means that only one plant is required to begin a new colony.”
During the 1980s in Canada, a close relative of M.parviflora doubled its population in five years to spread through wheat crops and slug growers with 30 percent yield penalties.
To prevent similar problems with M.parviflora in WA, the GRDC has supported UWA PhD student Pippa Michael to study the pest and inform management strategies.
One of the first stops for a scientist investigating control of resistant weeds is the livestock option – where animals are used to graze seeds that, in theory, lose their viability after digestion and so fail to germinate.
Ms Michael therefore studied the behaviour of M.parviflora seeds in the sheep rumen. Already, she knew that they passed straight through monogastric animals such as horses at a rate of up to 700 seeds per day.
What she hoped was that the micro-organisms unique to ruminants, which can break down stubborn carbohydrates such as cellulose and cellobiose, would also infiltrate the tough coat of M.parviflora and destroy the seed. There was bad news and good.
“When hard seeds with intact seed-coats were placed directly in the rumen, 93 percent remained viable after 48 hours,” she reports.
“But while dormancy was not broken by enzymatic digestion alone, the combination of mastication through chewing and exposure to the rumen may offer some promise, with 98 percent of previously damaged seeds losing viability after 12 hours in the rumen.
“If chewing provides the seed coat lesions necessary to encourage rumen break-down of M.parviflora seed viability, it could become a key method of control.”
On the other hand, if chewing does not inflict the necessary seed coat damage, grazing sheep will simply act as a taxi to distribute the seed further and aid the spread of the pest.
Research will continue at UWA this year to gauge how well sheep damage the seed before delivering the prognosis on their utility as a control option for M.parviflora.
GRDC Research Code: UWA 369, program 3