How to get rid of Crabgrass and prevent gardens from its regrowth

Crabgrass belongs to the family “Poaceae” in the Genus “Digitaria" which was first introduced into the US in 1849 as a prospective forage crop which later on turned into an invasive plant, and now it heavily infests some lawns and turf throughout the US during mid to late summer. Usually, its germination starts in late spring, grows throughout the summer, sets seed in late summer, and dies with the first frost. The Crabgrass seed remains dormant in winter to start germination in the spring.   

Origin & Distribution in the US 

Usually, two species of Crabgrass that exist throughout the US originated from the Asian countries bordering Europe. Digitaria ischaemum being a smooth grass and Digitaria sanguinalis a hairy and tall variety. Now, they are commonly found in vegetable gardens, turfgrass, and ornate landscapes all over the US. Generally, the large Crabgrass infests Agricultural lands, vineyards, and orchards whereas the turf grasses and lawns fell prey to smooth Crabgrass. Both of these types are highly adaptable to low fertile but moisture-rich areas. 

Identification 

Smooth Crabgrass 

It gains 4 to 6 inches in height, while light green leaves are an indication that it's ready to produce seeds which are the primitive cause of spread on a landscape or the turf. The underside of the leaves is hairy but, the surface of the leaves is smooth. Flowers are produced in pointed clusters on the branches, green in color. The noticeable patches sometimes form clumps that look ugly in the turfgrass. Mowing during the mature stages could disseminate seeds throughout the planting area. 

Large Crabgrass 

Large Crabgrass leaves may grow up to 5 inches long in a creeping pattern on the turfgrass gaining up to 2 feet in height. It spreads from the seeds disseminated due to late moving or from the nodes lying in the turf. When large crabgrass is ready to shed seeds, its leaves are hairy and light green.  

Lifecycle

In the US, germination starts after the last frost but, a vigorous growth period is between early to late summer. Both crabgrass species could grow with the start of spring depending on the temperature (50° to 55°F) and available moisture. However, they keep their pace slow during the spring and summer become the period of peak seed production. However, the areas lacking frost could allow crabgrass to continue growth throughout the year allowing the second crop in spring. 

Physiology & Growth Pattern 

After the crabgrass develops it clusters in any landscape, it becomes adaptable to dry conditions and high temperature due to the plant physiology and genetic makeup. A single crabgrass plant could produce about 500 tillers resulting in the production of 150000-200000 seeds per plant. They compete with the available resources meant for thriving garden plants and turf grasses. It is, therefore, a continuous threat that they will suppress the growth of both turf types of grass and garden plants.  

Fun Facts About Crabgrass 

Crabgrass is a staple grain in some parts of Africa where it yields more than 40 tons per hectare and is utilized for making flour, porridge, and fermented to make beer. It can produce edible grains in only six weeks in poor and arid soils. Whereas, it takes the shape of a weed when plenty of water is available. Since it's a low-maintenance grass, it can turn into livestock forage provided that it harvests before it sets seed. 

Crabgrass Control and Preventive Management 

Cultural Control 

The practices that help the minimum dissipation of seeds while moving the turfgrass can potentially reduce its spread in the lawns and gardens. Choosing a turfgrass variety that is best adaptable to your local climate could decrease crabgrass infestation. Overall, the health, vigor, and density of your turfgrass can stress crabgrass which is maintained by choosing the right fertilizers and irrigation, when they need it. Also, try to follow the mowing height for each grass variety according to the experts' recommendations. Be sure that the best adaptable turf grass varieties need heavy and consistent moving through late spring to late summer. Dispose of the crabgrass seeds contained in the movers away from the garden planting sites, properly. 

Mulching 

Mulching is another useful cultural practice that could stop crabgrass infestation in the garden beds, orchards, and around large trees by blocking the sunlight which is important for the sprouting of crabgrass seeds, their growth, and development. The best choice would be to spread wood chips, rice husk, or composted farmyard manure between 4-6 inches in depth for controlling weeds of all types including crabgrass. These mulches when left on the soil for longer could decompose and allow some weeds to grow. After Hand pulling, raking, and controlled burning, add a layer of the same mulching material to achieve the desired mulching depth. 

Organic Control 

Some herbicides prepared from plant sources can effectively control crabgrass and other weeds in the lawn. One such product prepared from the Cinnamon bark is "AgraLawn Organic Crabgrass Killer” which, when applied over the wet grass turf could kill Crabgrass in 3-4 days. It comes in a 2-pound shaker bottle and is enough for a 20 square meters affected area. 

Chemical Control 

Control with Pre-Emergent Herbicides 

A pre-emergent herbicide does well when applied before the crabgrass emerges out of the planting soil on turf grasses and garden beds. Chemical herbicides leave toxic residues on edibles so you may avoid them using on vegetables and orchards. You can select a pre-emergent herbicide based on its active ingredient after analyzing relative toxicity. 

Bensumec 4LF Herbicide 

The active ingredient in Bensumec is 46% Bensulide which is only sprayable on both cool and warm-season turfgrasses and ornamental plants. A 2.5 gallon is sufficient for applying on 1-acre of turfgrass in 100 liters of water using a high volume turf gun having low pressure.  

Monterey Weed Stopper II  

Another pre-emergent herbicide contains Trufluralin (43%) that can be used on vegetables and orchards before planting. It gives complete control on Crab grasses and other broad and narrow leaf weeds on both season turfgrasses. Mix one bottle in 2 Gallons of water to spray on 100 square meters of the soil prepared for planting turf grasses or vegetables. 

Control with Post-Emergent Herbicides 

Once the crabgrasses complete their germination, a post-emergent herbicide could perform well to stop its further growth. Usually, the post-emergent herbicides bring minor stress on turf grasses and other growth which replenishes once you irrigate and apply fertilizers. 

Gordon's Ornamec 170 Grass Herbicide 

It’s a selective herbicide containing 1.7% of Fluazifop that kills only the undesired weeds without damaging turf grasses and ornamentals. However, the yellowing of leaves may occur initially. It’s a slow starter but kills the targeted weeds including Bermuda grass and Crabgrass. The gardeners may use 2 ounces of concentrate per 1-gallon of water and spray on targeted weeds. 

GORDON'S Trimec Plus 

A brilliant mix of 2,4-D, Dicamba, and Quinclorac that targets more than 200 seasonal broadleaf weeds including crabgrass and foxtails. Especially for crabgrass, add 2 Ounces per gallon of water with a surfactant or 5 ml of any shampoo for complete adhering on the surfaces of the weed leaves. 

Learn How to control and get rid of other weeds in our complete Yard Weeding Guide.