These are the most common types of weeds that can damage your grass:
1. Creeping Charlie (aka Ground Ivy)
Creeping charlie is a very stubborn weed. It is most commonly identified by it’s purple flowers and round leaves. This weed grows low to the ground and quickly spreads across the lawn, choking out grass and small plants in it’s path. Creeping charlie thrives in shaded areas. Trimming back trees and shrubs will introduce more sunlight to the area and help thin out the weed. Keeping a healthy lawn is the best way to prevent a creeping charlie, or ground ivy, invasion. Thick, healthy grass will crowd out the weed, giving it little opportunity to grow.
Like creeping charlie, dandelions grow best in open, sunny areas and they spread very easily. When trying to manually pull dandelions, if the entire root is not removed it will regenerate and produce again. Dandelions are also known for their white seeds that blow in the wind and spread the weed. Not only will a regular lawn treatment program keep dandelions out of your lawn, it will also keep dandelions from neighboring lawns from spreading to your lawn.
Foxtail is hard to identify when it first starts growing because it has wide leaf blades that are very similar to turf grass. However, it will grow shoots with 3 to 10 inch seed bearing flowers. These flowers are yellow-brown with a fuzzy texture. This weed grows in both moist and dry soil and is tolerant to a wide range of conditions. Foxtail rarely grows in a well-kept lawn, however applying a pre-emergent herbicide is the best preventative.
4. White Clover
White clover is most commonly found in lawns with sparse, weak grass. It typically has 3 leaves and grows a white flower with a brownish-green center. It is a low lying weed that spreads across the lawn. Clover grows best in soil that has low nitrogen levels. Keeping your lawn well fertilized will help your existing grass become stronger and more resilient and also make conditions less desirable for clover. You can also keep white clover out of your flower beds by maintaining a thick layer of mulch around your plants. While you can hand pull these weeds, the best treatment for killing clover is regular herbicide applications.
Crabgrass thrives in bare, sunny areas in your lawn. It sprouts in late spring and continues to grow all summer long. Crabgrass is killed off in the fall by cold weather, but by this time the seeds have already spread and are preparing to continue reproducing next spring. There are various ways to treat for and prevent crabgrass, including: maintaining proper mower height, over seeding the lawn to reduce barren spots, hand pulling the weed and applying a herbicide treatment, and maintaining a lawn fertilization program to keep the good grass strong and healthy.
(From the website https://www.lawn-tek.com)