WEEDS have always been a problem in crops or pastures for their persistence in dominating valuable plants that are actually productive.
The traditional focus on weed control is to interfere with seed set and ultimately run down the residual seed bank.
But what can farmers do about controlling weeds that spread vegetatively?
What could possibly control a perennial weed with a huge network of roots that is able to produce multiple stems metres apart, propagate new plants from tiny root fragments and produce seeds that remain viable in the harshest soil conditions and in the gut of grazing animals?
These questions have long troubled researchers as much as farmers, and recent focus on silverleaf nightshade which affects crops and pastures across a wide area in southern Australia might provide a solution.
Murrumbidgee Landcare, Cootamundra, Project officer Phil Bowden said that silverleaf nightshade is of increasing concern in NSW, Victoria, South Australia and Western Australia, yet many landholders are unaware of the effect of the weed or how easily it is spread.
"Silverleaf nightshade has an extensive root system, linking plants across the paddock and up to several metres in depth, making control very difficult," Mr Bowden said.
"It competes with pasture and crops for soil moisture and nutrients, and does not respond to the usual chemical control measures."
Silverleaf nightshade infestations typically reduce crop yield by 20-40 per cent and render pasture unusable if it is not contained, according to Mr Bowden.
Mr Bowden also suggested farmers continue to be vigilant with their observation and control of the weed.
"They tend to grow in isolated hotspots," he said
"and are dormant at present but will get going in the spring."
A collaborative project between NSW Department of Primary Industries (DPI) and Murrumbidgee Landcare, with funding from Meat and Livestock Australia (MLA) and Australian Wool Innovation (AWI) is targeting silverleaf nightshade control across four states.
"The good news is that field trial results confirm that a 'dual action' control program, implemented over successive years can reduce the impact of this difficult weed," Mr Bowden said.
"The dual action program involves controlling silverleaf nightshade at the early flowering stage, both in spring or autumn, to prevent seed set.
"A follow-up spray in autumn controls re-shoots and helps run down the root reserves."
NSW Department of Primary Industries, Senior Weeds Research Scientist, Dr Hanwen Wu, Wagga Wagga Agricultural Institute said silverleaf nightshade is a weed of national significance.
"There are a lot of misconceptions about the plant," Dr Wu said.
"Farmers tend to treat it as a summer weed and spray when the berries are formed but it is too late as viable seeds are already set."
Dr Wu also supports the dual-action approach of specific weed control.
"Control during spring will kill the top before seed set, but the roots are not killed so before it is frosted in autumn we recommend chemicals to target the roots," he said.
Several herbicides, such as picloram, glyphosate, fluroxpyr and 2,4-D ester products, are registered for the control of silverleaf nightshade.
Consult with your local agronomist for advice on product choice, application rates and adjuvants, keeping in mind that application timing is more important than product choice.
"Crop and pasture competition can delay emergence in spring and suppress silverleaf nightshade over summer, however silverleaf nightshade stems will emerge during summer if there is no competition for summer rainfall," Mr Bowden said.
"Competition in spring reduces the number of new shoots that emerge and helps synchronise flowering, making herbicide application at flowering more efficient."
A series of workshops are planned for many of the SLN 'hot spots' around Australia in early spring.
For more information on SLN workshops and control strategies, contact Phil Bowden on 0427 201 946.
