<P> Mechanical weed control is any physical activity that inhibits unwanted plant growth . Mechanical, or manual, weed control techniques manage weed populations through physical methods that remove, injure, kill, or make the growing conditions unfavorable . Some of these methods cause direct damage to the weeds through complete removal or causing a lethal injury . Other techniques may alter the growing environment by eliminating light, increasing the temperature of the soil, or depriving the plant of carbon dioxide or oxygen . Mechanical control techniques can be either selective or non-selective . A selective method has very little impact on non-target plants where as a non-selective method affects the entire area that is being treated . If mechanical control methods are applied at the optimal time and intensity, some weed species may be controlled or even eradicated . </P> <P> Pulling methods uproot and remove the weed from the soil . Weed pulling can be used to control some shrubs, tree saplings, and herbaceous plants . Annuals and tap - rooted weeds tend to be very susceptible to pulling . Many species are able to re-sprout from root segments that are left in the soil . Therefore, the effectiveness of this method is dependent on the removal of as much of the root system as possible . Well established perennial weeds are much less effectively controlled because of the difficulty of removing all of the root system and perennating plant parts . Small herbaceous weeds may be pulled by hand but larger plants may require the use of puller tools like the Weed Wrench or the Root Talon . This technique has a little to no impact on neighboring, non-target plants and has a minimal effect on the growing environment . However, pulling is labor - intensive and time consuming making it a more suitable method to use for small weed infestations . </P> <P> Mowing methods cut or shred the above ground of the weed and can prevent and reduce seed populations as well as restrict the growth of weeds . Mowing can be a very successful control method for many annual weeds . Mowing is the most effective when it is performed before the weeds are able to set seed because it can reduce the number of flower stalks and prevent the spread of more seed . However, the biology of the weed must be considered before mowing . Some weed species may sprout with increased vigor after being mowed . Also, some species are able to re-sprout from stem or root segments that are left behind after mowing . Brush cutting and weed eating are also mowing techniques that reduce the biomass of the weeds . Repeatedly removing biomass causes reduced vigor in many weed species . This method is usually used in combination with other control methods such as burning or herbicide treatments . </P>

Why is mechanical weed control not the best weed control method