Scientific name: Digitaria sanguinalis, Digitaria ischaemum
Common names: Large Crabgrass, Smooth Crabgrass
Often confused with: Tall Fescue, Quackgrass,
What is Crabgrass?
Crabgrass is an annual grassy weed that infests lawns, landscapes, roadsides, agricultural and waste sites.
How to Identify Crabgrass?
There are two related crabgrass species common in the Northeastern United States, Large Crabgrass and Smooth Crabgrass, the former being larger overall and exhibiting more hairs on its leaves than the latter. This grassy weed germinates in late spring, grows slowly during the early part of the summer and then explodes in growth at the onset of oppressive heat. Crabgrass is a warm season plant that utilizes a different form of photosynthesis than the cool season turfgrasses that we use in our lawns. This explains why crabgrass is such a devastating weed – just as the cool season turfgrasses are going into dormancy due to heat, the crabgrasses are just coming into their optimal temperature for development.
How to Control Crabgrass?
As an annual grassy weed, crabgrass must be controlled on a year-to-year basis; crabgrass plants complete their life cycle in a single season and there are always plentiful seeds in the soil awaiting the opportunity to germinate. A single crabgrass plant can produce over 150,000 seeds that can lie dormant in the soil for years. The most effective protocol for control (not eradication – no product is perfect) is the use of pre-emergent herbicides applied before germination. Contrary to their name, pre-emergent herbicides do not actually prevent germination but rather stop the development of newly emerged seedlings. Crabgrass seedlings that escape control with pre-emergent herbicides can be controlled post-emergently with specialty herbicides. Success with post-emergent crabgrass controls is spotty due to resistence at various stages in the crabgrass plant’s life. A product that will easily control a new crabgrass seedling will be utterly useless during the middle of the plant’s life cycle, only to become very effective again as the plant reaches maturity.
Interesting Facts about Crabgrass
Crabgrass is a native of Africa, which explains its ability to withstand harsh climates. Imported to Europe and then into the United States as a forage crop for farm animals in the 1800’s, crabgrass escaped cultivation and now can be found growing anywhere there is sufficient light to facilitate germination.