Large crabgrass (Digitaria sanguinalis) is an annual weed found across New Jersey. It is commonly found on roadsides, fallow land, and in farm production areas. Large crabgrass can form robust root systems thanks to its numerous tillers and capacity to root at nodes, allowing it to out-compete crops for moisture and nutrients. Understanding the life cycle and biology of large crabgrass is key to figuring out the best options for its control on your farm.

Plant Description and Growth Habit

Large crabgrass reproduces through seeds. These seeds can survive in the soil for up to three years, depending on their depth from the soil surface. Plants emerge from the soil in late spring and early summer, once the soil temperature exceeds 50–58°F. In New Jersey, seedling emergence currently starts in late April and peaks in May before rapidly declining during the summer. Roots form at the nodes found on tillers of established plants, allowing for multiple plants to be formed from one plant when these rooted nodes are separated from the main plant. Flowers will set seed when the length of the day begins to shorten through the first hard frost. Plant density impacts seed production, which can range between 100 to 145,000 seeds produced per plant. Large crabgrass is frost-sensitive, grows best at high temperatures, and can withstand drought conditions. Roots can penetrate up to 6' deep in loam soils. Large crabgrass tends to be more prevalent and therefore a bigger issue in perennial cropping systems, such as tree fruit and blueberries, and in no-till fields when compared to annual cropping systems where there is regular cultivation. Large crabgrass tolerates a wide range of soil conditions, but grows especially well in well-drained soils, and responds positively to improved soil fertility. Characteristics of large crabgrass include:

• Appears in spring through early summer
• Sprawls across the soil with tillers producing roots at each node
• Seedlings grow upright and will produce tillers after forming 4 or 5 true leaves
• Stiff hairs are present on both the upper and lower leaf blade surface
• Collars are broad with hairs along the edges
• Mature stems will flatten and become red at their base
• Mature leaf blades can be up to 8" long
• Grows best in hot weather and full sun
• Tarping can create an environment that promotes large crabgrass growth

Management Strategies

Control of large crabgrass at the seedling stage (≤ 2–3" tall) is much easier to do before more extensive roots and tillers develop. Seedlings are easily killed by using weeders or rotary hoeing just after they emerge but before they start tillering. Weeding of larger plants should be done in a manner that exposes the entire root system at the surface, allowing it to dry and die, as partially buried plants can re-root and continue to grow. Organic and no-spray farming operations can utilize well-timed weeding and cultivation to kill newly emerged plants. Early detection and multiple control methods are needed to reduce the presence of large crabgrass throughout the farm.

Flame or steam weeders can be effective at controlling young crabgrass seedlings but will loose efficacy as crabgrass is tillering and growing taller. Because the growing point of crabgrass is located at or below the ground surface and protected by layers of leaves, the plant can easily generate new leaves after being exposed to heat.

Prevention

• Scout for early-season detection of large crabgrass seedlings, especially in areas where populations are known to be established.
• Clean equipment and tools used in areas where there are known, large crabgrass populations prior to using the same equipment in uninfested areas.
• Soil solarization with clear plastic can be used to kill seeds during the summer. However, it will likely not be effective before crabgrass emergence in spring due to low temperatures.

Weeding, Mowing, and Cultivation

• Persistent, early spring through early summer weeding of young crabgrass seedlings.
• Fallow fields should have regular cultivation during the first four to six weeks of warm weather to uproot young seedlings.
• Cultivate prior to tillering or rooting at tiller nodes.
• Grow crops that require repeated cultivation close to the production row to disturb young seedlings.
• Remove or mow established large crabgrass plants before they produce seed, typically between July and September.

Competition, Stale Seedbed, and Mulching

• A grassy cover crop that is established in the fall and is terminated in the spring before crabgrass emergence may slow down crabgrass emergence through cooling of the soil.
• Stale seedbeds, allowing a flush of weed seedling emergence followed by cultivation or flaming/steaming between bed prep and planting, and timed with crabgrass emergence in April and May, can reduce seed densities in the soil. Grasses will likely need multiple passes with a heat weeder to kill them because their growing point is below the soil.
• Crops harvested in late spring that are followed by stale seedbed practices and then summer plantings can disturb the crabgrass life cycle.
• In areas where large crabgrass is present, avoid growing crops that require little management during the growing season. Low management crops create an environment for large crabgrass seedlings to grow unimpeded.
• In areas heavily infested with large crabgrass, rotating into a sod crop for a few years can help reducing the infestation, if crabgrass emerging in the sod crop is not allowed to produce seeds.

Farm Decision Tool

Large crabgrass management is a multi-year process for farms not relying on synthetic herbicides. Identification and mapping of existing populations on the farm, along with reflection on your activities and how they impact these populations, is the first step to developing a management plan.

Use the charts below to identify your large crabgrass populations, your current management methods, and develop a plan of action to reduce large crabgrass from your production areas.

References

• Grubinger, V. (2004). Flaming Stale Seedbeds for Weed Control.
• Lounsbury, N., Birthisel, S., Lilley, J., Maher, R. (2022). Tarping in the Northeast: A Guide for Small Farms (PDF). University of Maine.
• Mohler, C., Teasdale, J., DeTommaso, A. (2021). Manage Weeds on Your Farm: A Guide to Ecological Strategies. USDA Sustainable Agriculture.
• Mohler, C., Johnson, S. (2009). Crop Rotation on Organic Farms. USDA Sustainable Agriculture Research and Education.
• Northeast Cover Crops Council (2021). Cover Crop Decision Support Tools.
• Uva, R., Neal, J., DiTomasso, J. (1997). Weeds of the Northeast. Cornell University Press.

August 2022