Crabgrass and Johnsongrass are two types of weeds that arrived in the United States from other countries. Johnsongrass was brought to the United States in the mid-1800s as a feed crop. Crabgrass came to the United States as a stowaway in grain imported from Europe. There are specific differences and methods for identifying the grasses to determine how they might interact in your farm or garden.
Crabgrass is a lawn and garden weed that is common in bare patches of land. Crabgrass looks like a circular nub of grass with light green or purple leaves. If left unchecked, it will sprout flower stalks that look like antennae or bird feet. Johnsongrass is a tall-growing weed that can choke out agricultural crops. It has been declared an invasive species by the U.S. Department of Food and Agriculture. Johnsongrass can be up to 18 inches tall with rhizomes about the size of a thumb. A rhizome is a stemlike part of the plant that grows horizontally underground.
Crabgrass and Johnsongrass can be treated with good watering, fertilization and soil preparation techniques in combination with the application of pre-emergence herbicide. Pre-emergence herbicide kills weeds before they grow from seed. Pre-emergence herbicide should be applied in the late spring, around May, before the weeds germinate. Because crabgrass and Johnsongrass are perennial weeds, meaning hey don't die off every year, it is almost impossible to control an outbreak with only one herbicide application. Often, a gardener will need to apply herbicide every year to keep crabgrass and Johnsongrass from returning.
Types of Crabgrass
Hairy crabgrass and smooth crabgrass make up the two primary types of crabgrass. They are similar in appearance except that one of them has tiny hairs on the blades and the other one has smooth blades with no hairs.
Herbicides should be applied with care to avoid contaminating the environment or your drinking water. Read the manufacturer's instructions completely for use and dangers. Wear protective clothing that covers your whole body, including long pants, long sleeves, gloves, a face mask, and protective boots. Properly dispose of the herbicide containers at a facility recommended by the Environmental Protection Agency.
Johnsongrass is sometimes confused with Shattercane grass because they are very similar in appearance when they are small. Shattercane is annual and dies off each year, while the perennial Johnsongrass will persist for at least two seasons. When Johnsongrass matures, it can grow to be over three times as tall as the tallest Shattercane grass.