Blue heliotrope (Heliotropium amplexicaule) and rock fern (Cheilanthes spp.), two potentially poisonous weeds can come as a shock to unsuspecting new property owners.
I raise blue heliotrope and rock fern as issues as they are endemic on many properties across central and northern NSW.
In the case of blue heliotrope, it is mainly a summer grower and can commonly be not easily seen over winter and early spring.
Rock fern is commonly present but not a standout plant.
Both weeds tend not to be readily eaten by sheep and cattle but when all other herbage is eaten down, like in a dry summer and/or autumn, especially with new animals to the property, stock losses can be quite high.
Fighting “fire with fire” is critical to the success of defeating weeds like these, as well as against others like galvanised burr, khaki weed, catheads, Bathurst burr, dwarf marigold, Coolatai, African lovegrass and fleabane.
The stronger the tropical perennial grass pasture (density, vigour) the greater its ability to outcompete weeds. While in some cases weeds can’t be totally eliminated, because of factors like reinvasion from public roadsides (blue heliotrope, Coolatai grass and African love grass are good examples) strong perennial pastures can ensure they will, if at all, only reinvade very slowly.
Summer weed problems in pastures are to a large degree a consequence of lack of competition from summer active perennial pastures. Control therefore revolves around replacing them with competitive summer perennial species.
Often summer weed problems are worse after a cropping phase where no summer active perennial pasture has been re-established.
Summer growing perennial grasses like Premier digit and bambatsi panic grow at least at the same time as most summer weeds and more importantly begin strong growth earlier and finish later than most of these weeds. They therefore compete “head on” with them.
Before establishing tropical perennials, it is important to largely eliminate the weed seed bank.
Generally a three year summer fallow with total weed seed prevention plus winter cropping is enough to eliminate the soil seed bank of most weeds.
Also three years provides ample opportunities to kill out existing plants of weeds, including troubling ones like blue heliotrope.
Correcting soil deficiencies like phosphorus and sulphur, winter legumes that suit any given weed infected paddock, such as serradella sub clover and biserrula, and grazing management to ensure sound persistence of the main pasture species.
Next week. Walgett not a marginal cropping area says leading agronomist/farmer.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.