Quackgrass and Crabgrass are two graminaceous plants that we have a tendency to confuse, but that are very distinct. They are annuals that spread through seeds or underground root systems.
Both can quickly become very invasive and even potentially destroy your lawn.
Plant growth is rapid when temperatures are 20°C and higher with elevated levels of humidity.
Here is some additional information.

 

1. Quackgrass
2. Crabgrass