Birds and other animals, wind and water are widely accepted as vectors of environmental weed seeds and other propagules. In addition, the role of humans in deliberately and accidently moving plants around the landscape by buying and selling ornamental and agricultural species and unthinkingly dumping garden rubbish is also well recognised. That our vehicles and other machinery can also spread weeds may be less obvious.
Weed Seeds
Soil containing seeds can be carried readily and some seeds may adhere directly to the surfaces of machinery and vehicles. Fine seeds are found in high densities in soil, particularly in disturbed environments such as roadsides
Many weed species, such as grasses, produce enormous numbers of seeds. Serrated Tussock Nasella trichotoma is a South African grass naturalized in southern Australia. A single plant can produce approximately 80,000 seeds in one seed set, and these seeds are readily spread on farm machinery. Palm Grass Setaria palmifolia is another grass species that spreads along roadsides when seeds are picked up by roadside slashers.
Stem and Root Fragments
Plant material may cling to any machinery, but a slasher or mower is particularly likely to pick up plant segments, including stems and roots that may be capable of establishing. In subtropical Australia, Freckleface Hypoestes phyllostachya, Morning Glory Ipomoea indica and Singapore Daisy Sphagneticola trilobata are examples of weed species readily spread when plant pieces are carried by machinery.
Spreading Smashed Plant Parts
Machinery such as a side arm slasher is capable of smashing trunks and branches of plants such as Coral Tree Erythrina x sykesii. Pieces are sprayed in the immediate vicinity of the source and fragments of this species are capable of rooting where they contact the ground. A single stem of Coral Tree can quickly be converted into a potential thicket, either when a trunk is felled and vertical shoots arise along its length or when scattered individual stem sections take root and grow. Madeira Vine Anredera cordifolia is another plant liable to spread as a result of damage to the parent plant. Aerial tubers from the stems of this vigorous climber can be knocked to the ground under and around the parent vine.
Avoiding Weed Problems
Weed dispersal by machinery can be avoided or minimised. Machinery should be cleaned, before and during jobs. Weeds susceptible to machinery dispersal on roadsides and other work areas can be identified, signposted, flagged or fenced off so that alternative methods of weed control can be applied in such areas.
Barbara Stewart - I am an Australian ecologist based near Byron Bay on the east coast of the continent. My interests revolve around trees, forests and ...
