Now this may sound strange, but fertilizer can help control the weeds in the yard. But, it is not as direct as what you may be thinking or hoping. The fertilizer itself will not control the weeds, but it can help your healthy lawn to control the weeds.
Now that introduction only seemed to complicate things. I first want to make sure that I have not muddied the waters, so here it is, fertilizer itself will not control weeds. There. But it does aid in the process by creating healthier grass plants.
Healthy grass plants can help to control weeds by themselves. Weeds are competition for grass, when the grass plant is stronger, the grass plant can more easily win the battle for space, water and nutrients. When the grass plant can out-compete the weeds, there will be less weeds in the turf stand.
If your lawn is weak already, just fertilizer will not get your lawn to where it needs to be to fight off weeds on its own. The first things is to get the existing weeds under control. Then you have to manage the water and fill in any bare spots in the turf stand. You have to get the lawn into a very healthy state before you will be able to get good long-term control of the weed problems in your lawn.
However, there is still a chance that weeds will invade your lawn. This is when you need to do more than fertilize and chemical or mechanical controls are needed. Just remember, when ever you use chemicals, as follow the label for using the product.