Killing Weeds in your Lawn
The internal biologial make up of weeds and grasses is different. The weeds, like trees and shrubs have Cambium Cells. These cells provide support in the main trunk and branches of the tree or weed. The selective weed killer is a growth hormone that mimics the actual growth hormone 'Gibberelline' - the plant hormone responsible for secondary thickening. The selective turf herbicide is absorbed by the weeds and after a while, the weeds go into super growth, with their stems twisting and distorting. The weeds actually outgrow themselves and when their overall structure has literally had it, they die. Grasses do not have Cambium Cells so although they might absorb some of the chemical, it has no affect - if applied correctly in the first place!
One of the other early flowering turf weeds is Slender Speedwell, which exhibits tiny blue flowers. It is a challenge to kill it and early application of a selective herbicide is advisable. Once it has finished flowering, control is said to be too late. You can control it with Vitax Lawn Clear. More than one application may be required 6 weeks apart.
For advice on total weed control products, you might find this article on Total Weed Control useful. These products should not be used on your lawns unless you want to kill them off totally and start again.
To help you see where you have sprayed your lawn weed killer, why not add Indigo Garden Spray Dye to your sprayer?
Visit The Lawn Shop for some lawn weed control products