With Balan 2.5 G Herbicide being a pre-emergent, it can either be applied in the fall or spring and how often it is applied depends on the program you are following, ie split application or single application applied per the product label. The general rule for spring is to apply your pre-emergent herbicide treatment after the ground has thawed from the winter but before the temperature of your soil reaches 55 degrees, as that is when crabgrass begins to germinate. Other weeds will germinate when the soil temperature is between 55 and 65 degrees. You can use a soil thermometer to determine the temperature of your lawn/area. You will want to measure the temperature of the soil a few inches below ground. The ideal time to apply a fall pre-emergent herbicide to your yard is between August and November when the soil temperature is below 70 degrees and dropping.You may contact your local cooperative extension office to determine the correct timing of the application as this will vary greatly from region to region or search online for best time to apply in (your area).  A lot of universities have great articles for this. There is also a tool here that can tell you the soil temps