There are numerous ways that weed seeds can enter farming systems including the soil itself referred to as the weed seed bank, seeding weeds, wind, livestock and other animals, fodder, farm machinery, waterways and contaminated crop seeds. Weeds produced in other countries carry the added risk of introducing alien and invasive weeds. Contaminated crop seed has been a key source of new weed-seeds. It is recommended that clean seeds be used.
Other sources of weed seeds include mulches, manures and composts. When using these substances as soil improvers and weed suppressors, it is important that composting is performed correctly to essential that no viable weed seeds remain. One way to accomplish this is by insuring that the compost reaches the right temperature to destroy any weed seeds which may be in the compost. It is also necessary that the compost is protected from sources of contamination such as windblown seeds.
Identifying modes of weed dispersion and reinfestation through the harvesting process is vital in preventing and minimising future weed problems. Crop harvest is a crucial time for weed seed dispersal and therefore it becomes vital to thoroughly clean all harvesting equipment to avoid weed seed dispersal and reintroduction. Weed seeds which become lodged in farming equipment are easily carried to other fields unless thorough cleaned.
Field margins can also be a potential source of weeds and holders of weed seeds as vacant areas are particularly prone to weed infestation. One way to help reduce this is through planting native grasses or wildflowers in the boundary strips. Cover crops and ley help to prevent weed seeds falling onto the soil where they germinate or lie dormant until conditions are favourable for germination. Cover crops and ley also increase the chances that the seeds will be eaten by animals and insects.
Planning and implementing a farm hygiene strategy minimises the risk of adding weeds to the seed-bank from external sources. The benefits of planning and implementing good on-farm hygiene include the following:
Weed seeds will not be added to the seed-bank from other areas of the same paddock, other paddocks on the same farm, other farms or other regions.
Management costs will be reduced in the long term.
Weed problems will be quarantined or confined to known areas where they can be more effectively managed.
Weed importation and spread can be impeded at several critical points, specifically:
Sowing of the seed
Fence-lines and non-cropped areas in cropping paddocks (eg water courses)