Q. What steps can be taken this time of year for crabgrass invasion?
A. It is now August. If you correctly identified your weed as crabgrass, there is nothing that you can do now except remove them by hand or do some hand weeding. Crabgrass will die when it freezes hard this winter. If it is in a location where it does not freeze, or lightly freezes, then it will survive and grow more the following year.
All you can do this time of the year is soak them with water and pull or rogue them out.
You can also burn them back if it is allowed. Propane weed flamers or torches work well if you use them in an area that will not continue to burn. The seed, however, will still be there on top of the soil and unaffected. The seed germinates in the spring around the middle of February in our climate or perhaps earlier if it is warm. I purchased one for weed control on my small farm in the Philippines. The more powerful ones like mine will even weeds that are wet or after a rain. Very important in the Philippines.
Flame weeder I purchased
Pre-emergent herbicides or weed killers can be applied about the middle of January to prevent crabgrass from germinating and getting a foothold. It should be reapplied about six weeks later or when the label tells you to. But this time of the year, all you can do is pull, burn or dig them out.If you buy a pre-emergent weedkiller for crabgrass make sure it lists crabgrass on the label, destroy any crabgrass that survive past the end of January and apply this herbicide by mid-January in our climate.