St Barnaby’s thistle, a typical common problem weed that one would rather not have, emerged in several paddocks on our property this year. Cause of infestation was almost certainly in one of the batches of pasture seed we added to our pastures last autumn.
If one doesn’t want a new weed that is likely to cause problems, sometimes big ones and ongoing, a few things are important.
Early identification and a strategy to prevent weed seed set, especially in the first year before it gets away (one weed plant can set hundreds if not thousands of seeds) is critical.
St Barnaby’s thistle, like many weeds, has a proportion of it seeds “hard” which means they can remain dormant for at least a few seasons and then germinate and become a problem.
It is a widespread problem in our area (and many others) and we were well aware of what it looks like (an important aspect of eliminating early before it gets away).
In our case St Barnaby’s was scattered across five 20 hectare paddocks with around one to three plants per hectare.
Such a low rate could easily have been a trace contaminant of one of the several pasture seed lots we used for autumn addition to perennial based pastures.
Four-wheel bike surveillance and plant removal by us was practical in this situation with plants removed prior to seed set. Repeat surveillance will be necessary next spring.
We have also found what I regard as a major threat if left unattended, blue heliotrope, a perennial deep rooting creeping potentially poisonous weed. Prompt deep removal plus using residual herbicide pellets of tebuthiuron(200g/kg) has been used for isolated plants not close to trees or waterways.
A sensible biosecurity strategy for all properties, especially newer property owners, is to firstly establish what weeds are present on a property. What threat they pose to yourself and neighbours if not contained or eliminated is important.
Knowledge of likely threats in given areas is critical for early elimination. Constant surveillance is important, especially on boundaries (including public roadways) and entry point to a property. If showing people around best to use your own vehicles. Surveys have often shown visiting vehicles may have many weed seeds present in them.
Biosecurity entails more than just weeds. Some diseases and pests like nematodes can be transferred to a clean property via man, vehicles and machinery. Feral pigs can bring in diseases and native or feral animals are capable of transferring weeds onto a property, including birds.