Weeds The majority of turf weedkillers available to the amateur gardener are limited in their effectiveness against some lawn weeds.  Broad-leafed weeds such as Plantains, Cats Ear, Hawkbit and Buttercup are reasonably easy to control and will often require at least 2 or 3 applications during the Spring/Summer.  However, small leafed weeds such as Speedwell, Selfheal, Yarrow and the Trefoils are resistant to commonly available chemicals and the only recourse may be to seek assistance from a specialist who is trained in pesticide application.