Hello: There are a number of diseases and insects that could be involved with lawns turning brown. Grubs could be a work below the soil line and this is the time of year when the most damage can occur. There are several diseases that could also be present at this time of year. There are a lot of variables involved when tryng to determine the exact cause of a lawn problem. Typically pesticides today do their job and are quickly disipated by the sun, diluted by soil moisture or inactivated by soil micro-organisms. Air and soil temperatures also are factors. You should contact your lawn care company and find out what materials were applied and be sure to express your concerns about how your lawn looks and time frame between time of application and symptoms.