Understanding Weed Seeds

Next year’s weeds start with this year’s seeds. The risks of herbicide-resistance evolution have been shown to increase with every increase in initial seedbank size. By understanding how seeds spread, you can reduce future challenges.

Preventative weed management incorporates practices that avoid introduction, infestation or dispersion of weed species into areas currently free of those weeds. Natural seed dispersal in the absence of a specialized dispersal mechanism or agent is generally limited to less than 5 meters from the mother plant, and often, human activities are responsible for weed seed dispersal.

Some weed seeds are more adept at spreading.

Seed quantity – A single waterhemp plant can produce more than a million seeds. Palmer amaranth can produce more than 600,000 seeds per plant. Weeds that produce larger quantities of seeds can rapidly overtake fields and spread herbicide-resistant genes.

Seed dispersal – Seeds can spread through blowing, floating and even by animals. Some weeds possess specialized adaptations that aid long-distance dispersal. Horseweed seed regularly disperse as much as 500 meters from source populations and have been recovered from atmospheric currents at about 140 meters above ground level. Barnyardgrass seed typically float in water and can be transported through irrigation water for up to several miles.

Seed longevity – It varies between species. Dormancy allows herbicide-resistant genes to persist over several years in the soil seedbank. In general, the larger the seed, the more persistent it is in the soil.