Have you ever read the label on the weed and feed, or the chemical fertilizer you use? Does it contain Atrazine? Did you know, than in order to apply weed and feed, or any other pesticide in a property other than yours, you are required by law to have a pesticide license? Or that you should wear personal protective equipment, when handling these type of products?
Weed and Feed contains Atrazine, which is an endocrine disruptor. In tap water, 59 Pesticide Residues were found by the USDA Pesticide Data Program. Atrazine, and 2-4D (agent orange), are found in almost 90% of the water samples. Some of those pesticide residues found in the water are known carcinogens, bee toxins, and hormone disruptors, among others. So, why people still use those products? I believe the main reason is just lack of knowledge, and in most cases people simply don’t care.
Is very stable, so it can persist in the environment for a long time. Over 3 months in the soil, and will remain in groundwater for decades. Atrazine, easily leaches into the soil, so it is a big problem, since most people don’t follow the directions given by the manufacturer of the chemical pesticide and fertilizer. Once again, using this type of products goes against the systems approach to organic land care. Atrazine will kill the weed, and will pollute the soil and water, but will not fix the problem of getting rid of weeds, since weeds will grow in exposed soil.
My advice is, fix the soil. Make sure the soil environment is not propitious for the weed seed to germinate and thrive. What I would do is first of all take a soil sample, reseed those bare spots, let the grass grow a little bit taller during the growing season, so it can go to seed. Include some organic fertilizer to feed the microbes. Spray some compost tea. And ultimately, be patient.