I would avoid using the weed and feed since the time to weed and the time to feed are not the same, and many of these product can weaken St. Augustine. In short you can fertilize that lawn with a product containing a 3-1-2 or similar ratio of nutrients in mid to late spring and again in early fall. Divide the first number on the bag into 100 for the pounds of fertilizer to apply per 1000 square feet of lawn area.
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