We have had this invasive weed in our lawn for two years now. It looks something like the pictures of crabgrass on this website with an enhancement. It sends out very long feeder branches along the surface of the soil that are difficult to pull out. My husband applied a fertilizer with a crabgrass preventer once in March and once in April but I would like to be sure we are really dealing with crab grass so that we can get rid of it once and for all.
Garden Counselor ANSWER:
There are several things I can suggest to help you isolate the characteristics that will identify this weed. There is a possibility it may be bermuda grass, which is much more difficult to deal with, so I hope you are correct.
1) Accurate crabgrass identification requires that you look at the lifestyle because it is an annual weed. It will die each winter, although new plants coming up from seed in the same spot may give the impression that it is the same plant.
Bermuda grass is the other possibility, and it survives through the winter, though it goes dormant. The crabgrass will die, turn completely brown, and if you pull it up later the roots are also dead. Bermuda may go into various degrees of browning, depending on the cold. If you dug up a deep section of roots you would notice viable tissue in the rhizome area. (See these crabgrass pictures on the site.)
If you can determine whether or not the same plant has survived through the winter, and the existing runners green up the same time as the main plant, then it is Bermuda.
If the weed has to grow out from the center sprout first, before it sends out new runners, it is probably crabgrass.
2) Proper crabgrass identification looks at the root system and also how the plant spreads. If you dig up an established plant, crab grass will have only ordinary fibrous roots. Bermuda grass has similar fibrous roots that will all being growing downward. It also develops the more substantial rhizomes that grow out laterally, and at some point, put out vertical shoots that head to the surface. So while crabgrass and bermuda both can exhibit runners above ground, only bermuda has runners below ground. These rhizomes can be close to the surface, or at a deeper level.
When you try to dig out bermuda grass, be careful. Any of these rhizomes that break off, if they leave behind a section with a junction node, are capable of sprouting into a new plant. It is extremely difficult to eradicate it by pulling because of this. (See these bermuda grass pictures on the site.)
The feeder branches, as you call them, or runners, are also known as stolons. They can be difficult to pull out for either variety, but the buried rhizomes are the determinant.
3) The double application of crabgrass preventer should give you a lot of protection this spring, and into the summer. Thus, if you start seeing the weed in question, I would suspect that it is probably not crabgrass, which could only grow from seed, and should be inhibited by the pre-emergent, if that was applied accurately. The bermuda, even if the top growth was removed, could still come up from an underground rhizome. So if you see the appearance of a potential aggressor, carefully dig it up from a depth sufficient to bring with it the entire buried rhizome that is sending up the shoot, to confirm this.
4) Lastly, crabgrass as it develops fully has a characteristic floret pattern. If you rub your hands over the center of the plant, you can push down all the blades and runners and see a definite center with everything radiating out from it. A large bermuda grass plant may have stuff growing out from the single plant, but it will be very haphazard, like tussled hair, going every which way from various starting points.
Hope this info is helpful for you. Crabgrass identification is a critical concern for many people, especially in the late winter, early spring period when they hope to get ahead of it.