There are a wide variety of weed problems with pyrethrum and each are often dependent on country, and regions of country where pyrethrum is grown.  With this said, it is clear that weeds often have a most detrimental effect on pyrethrin production and yield.  Pyrethrum per acre if often less than half normal yields, and perhaps a low as one fourth normal yields if weeds are not controlled.  While Australia uses herbicides to control weeds, East Africa relies mainly on organic methods; that being manual weeding.  It is important that weed management is most problematic the first year.  Once the crop is established, weeds are typically easier to control and have less negative impact on production yields.