First you need to make sure chemical tracking is enabled. Certain industries like Pest Control have it enabled by default, but if you're unsure if it is enabled or want to enable it for your business, start by going to the Manage page, which can be accessed by clicking gear on the right of the top navigation bar. On the Manage page Enable chemical tracking? will either be set to yes or no. If it's set to no and you choose yes, you'll be taken to the chemical mixtures management screen. If chemical tracking is already enabled for you and you don't have any mixtures, click the Update the chemical mixtures you use link.
You'll need at least one chemical mixture, so on the mixture management screen click the Add a mixture button. Adding a new mixture requires a chemical name and EPA registration number. You'll also need to choose how much of the chemical is used in the mixture and the dilution rate. When finished, click Create this mixture.
Chemical treatments are tracked on a per invoice basis, so when you create an invoice you'll be asked if you want to track any chemical applications with it. If you choose yes, you'll be taken to a page where you can add one or more chemical mixtures to the invoice. To add a mixture, select the chemical mixture you used, the area it was used in, and the pest you were targeting. Another application can be added by pressing Add chemical application. When finished, press Save applications.
You can go back and add chemical applications to invoices that have been created by going to the invoice's detail screen, opening the blue popover menu in the top right, and choosing Update Chemical Applications.
Adding chemical applications to invoices means that when you send invoices to customers, they'll see a detailed list of all the chemicals and where they were used on a job. The job's detail screen will also show a history of chemical applications.