Latin: Digitaria ischaemum
Crabgrass is a summer annual. It germinates when soil temperatures reach 60 degrees Fahrenheit. It will begin to appear in most areas in May. Crabgrass germinates first in hot spots and by June will have come up where it is going to, although you may not notice it until later in the season.
There are many anecdotes on crabgrass timing, for instance, forsythia blooms occur at the same time crabgrass is germinating. Many of these anecdotes are nothing more than vague patterns in timing. Remember many plant blooms are reliant on air temps, while crabgrass is dependent on soil hitting 60 degrees.
Look for crabgrass along roadsides, curb lines, and other areas of turf that touch something that heats up. The hotter the soil gets the more crabgrass will be able to thrive. Smooth crabgrass also will appear in thin or bare areas in the lawn. Initially the weed will look like a lime green grass and will remain grass like until the second or third tiller stage. Crabgrass can, with neglect, take over entire areas of lawn in one season.
What to expect
Crabgrass will first appear in late spring. Crabgrass can come up in spite of pre-emergent control measures. It must be controlled post emergently, early in its life cycle. If crabgrass is allowed to reach the four tiller mark (a tiller is a fancy way of saying individual leaf/stalk ) it will become much more difficult to kill, in fact most labels for control products, such as Drive 75df, Quincept, and MSMA, state the difficultly of control is greatly increased after this point.
That being said you can prevent crabgrass with 95% efficiency if you are very deliberate in your control measures.
I recommend applying an early pre-emergent herbicide to just hot spots as a preliminary treatment. I like to use the product, Barricade 4fl (prodiamine). I mix it in a backpack or spray tank at the middle rate and treat along my hot spots and any historically bad areas.
Next I treat the entire lawn with my first fertilizer application in April using the product, Dimension (Dithiopyr). I like to make sure I go heavy with this treatment and I treat the edges twice, or once moving very slowly. The last pre-emergent is another treatment of dimension, this time liquid. I apply the dimension the same way I applied barricade in the early season, making sure to hit hot spots and scouting for any germination. Dimension will act as a post emergent control up to a certain point.
If crabgrass has come up and is in a mature stage you can use Drive 75DF (Quinclorac) to treat. I only like using a backpack at this point because it can treat in a specific targeted way. I usually mix at a rate of .45 Oz of Drive 75DF per gallon of water and soak the entire plant. It is very important not to over treat the crabgrass with this mix, it can and will burn grass if misused. Just treat the crabgrass plant and avoid over spray off target.