Saturday, August 13, 2011

Johnson Grass

There are some plants that are recognized by many people as being noxious weeds. One of those is Johnson Grass. These towering grass plants with their broad strapping leaves are a major weed of agricultural fields and cost farmers a lot of money each year in spray costs and loss of production. Seeds travel widely in flood water and as passengers on farm machinery. If you are trying to convince people that management for native plants is a proper thing to do, you definitely don’t want such a well known weed growing where everyone can see it. I battle with this plant every year and most of my trouble is within sight of the road. New seed is regularly deposited on the roadside by farm equipment, road maintenance equipment and vehicles that snag plants crowding the edge of the road.

The origin of one patch of Johnson Grass is something of a mystery. It’s a fairly new infestation, but it’s nowhere near a road. It sprang up on the site of a patch of Poison Hemlock that I eradicated several years ago. The hemlock is now gone, but Johnson Grass has taken its place. I know that the bare ground resulting from the loss of the hemlock was perfect for colonizing Johnson Grass, but I don’t know where the seed came from.

Fortunately, Johnson Grass is not found in the established high quality prairies, so I don’t have to worry about protecting rare plants when I go after the weed. An easy way to destroy small patches is to mow the grass in late July, wait for the grass to shoot back up and spray it with glyphosate herbicide.

Johnson Grass regrows much more quickly than most of the other plants, so it’s possible to spray the site without killing everything else. Even if everything else dies, that’s better than letting the Johnson Grass live. In the thickest patches of Johnson Grass, there’s really not much else growing anyway.

For patches this size, I use a backpack sprayer with a flat fan spray nozzle. This gives good coverage on the target plant and makes for a more controlled placement of the herbicide. That spray wand looks like the heat ray weapon on the Martian flying machines in the original War of the Worlds movie. Maybe if I dye the spray red, it will give the plants more of a scare.


  1. I have seen more Johnson grass this year than ever before. It is all along the roads in SE Ohio and in the neighbors alfalfa as well as my yard. I saw large patches all along the roads on a recent trip to Tennessee. Does anyone know why it is so prominent this year?

  2. Johnson Grass responds best to heat and moisture, two things we've had in abundance this summer. A second factor is the apparent delay on the part of some State and County maintenance crews to mow along the roads. Probably a budgetary consideration. On one state highway, I had Johnson Grass whipping the side of my car as I drove by. They still mowed before the seed developed, but the grass was much more visible this year.