I agree with John, Chemlawn is one of the most unreliable lawn care companies out there. It is the "big business" of the lawn care industry, and they have lost touch with the home owners needs, and zero in pretty much on the almighty dollar.
Their salesmen are paid by commission, so in order to close a sale, they drop the price. (Better some $$ then no $$ in their minds)
Their techs have to make a quota of $$ serviced each week. So if their lawns are oversized and under priced, they tend to fly through them, resulting in less then a good job.
Most of the techs will only put up with the company for a season or 2, so it is very rare that you find a seasoned lawn tech working for them.
That is probably why they have the lowest customer renewal rate on any lawn care company in the area.
There is a chemical that can be used called "Drive". Dallisgrass is not on the label, but I have been seeing good control, while the
plants are still young. However, once the
plant matures, good luck!
I am not sure if Drive is available to the home owner in your state. I believe it is considered to be a "restricted use pesticide" in some states. Meaning that only a licensed applicator may purchase and apply it.
Since it is not listed directly on the label, you may have a hard time getting a lawn care company to use it.