My son is 9yrs old, he has a very dry cough, I took him to the e.R and they did him an astma treat, what can I give him for the cough.

Appointment M.D. The cough may be a sign that his asthma is worsening or is not under good control. Your doctor can provide a peak flow meter for home use and outline his baseline and the signs of distress. In general, an albuterol inhaler is used to quickly relieve asthma symptoms.
Follow action plan. Everyone with asthma should have been given a written asthma action plan. This is a step by step guide to follow when asthma symptoms occur. The plan should indcate how much albuterol and how often, an adjustment to inhaled steroids and when to start oral steroids. The plan should outline symptoms and when to call the doctor. If you don't have a plan, see an allergist (asthma specialist).
Inhaler. Many children with asthma cough when they get a flare up. Did the people in the er give you an inhaler for home or just treat him with it there? Talk to his regular doctor. Dry cough can come from a virus infection or it can also be a sign of asthma with a sudden flare. It will help for your doctor to know how it went in the er.