Content: Weeds with running rootstalks (rhizomes) are difficult to control. We explain why. Then we give a simple, no-cost way to control rhizome weeds. We use Congo grass (Imperata cylindrica) as an example. It is one of the world’s ten worst weeds. Cut Congo grass to form a mulch. Plant a food crop of viny legumes to smother the grass. Finally, we suggest how black beans smother weeds in growing maize.
The reason is that instead of having roots that just grow straight down into the ground, these weeds have one main root that grows along in the ground parallel to the surface. There are joints or nodes in these roots that are quite close together. A new plant can grow up above the ground from every one of those joints. Roots like this are called running rootstalks.
If you break off a piece of that rootstalk, a new plant will start to grow from that piece, and a new running rootstalk will also begin growing from that small piece! So when you hoe or cultivate weeds with roots like this, they just grow more and more as pieces of the roots get cut or broken off and are spread around in the soil.
Of course there are expensive chemical weed killers (herbicides) that some people use to get rid of weeds like this. Another way is to keep hoeing these roots out up on top of the ground where the hot sun will dry them out and kill them. The problem with this method is that it takes a lot of hard work, and you never do get all of the roots out of the ground before they start growing again.
A very good method of dealing with this problem, however, is to smother the weeds! The idea is that during the season when they would be growing well, you cover them completely so they can’t get any sunlight at all. Without the sunlight, they just die, and their roots die too. But how can you smother a growing crop of a really bad weed grass like Congo grass, for instance? It is one of the ten worst weeds in the world! It grows from a running rootstock.
Well, in northwest Thailand, they’re killing Congo grass by smothering it with other plants, actually with thick, viny legume plants.
Perhaps you might want to try this method yourself. If you do, Klaus Prinz of the McKean Rehabilitation Center near Chiang Mai says that, during the rainy season, when the grass has grown to between 1/2 a metre and one metre (1-1/2 and 3 feet) high, you should cut it off close to the ground. Leave it lying as a thick mulch, evenly spread all over the surface. As soon as it’s been cut, plant the seeds of a viny legume right down in the mulch. The seeds could be 30 centimetres (one foot) apart in rows 1/2 a metre (1-1/2 feet) apart. Klaus suggests that you select a viny legume that will produce a crop of peas or beans that you can harvest and use for food, such as cowpeas, ricebeans, or lablab.
The legumes will grow quickly and will start climbing all over the grass mulch. Of course, some grass will also grow up through the grass mulch from those running rootstalks that are still living down in the ground. Here’s what Klaus says you can do about that. He says to get a straight stick, bamboo would do, about two metres (six feet) long. Then, step by step, go over the plot or field pressing the stalks and leaves of growing grass down on top of the mulch. This will give your legumes a chance to grow over the grass you’ve pushed down. Before long, your crop will be growing very fast because all that mulch that it’s growing in will hold every bit of rain that falls into it. Also, the legumes will be adding valuable nitrogen to the soil.
Now see what you have: a layer of mulch made up of the grass you cut, together with some grass that grew up afterwards. And it’s totally covered with a viny legume food crop. No more grass can possibly grow from those rootstalks down in the ground because the dense cover on top doesn’t let any light in. Now, because no grass is growing from the roots, they’ll start to die down there in the ground. And while this is going on, when your viny legume crop matures, you can pick the pods off the vines. You will have been making good use of the land while controlling the grass.
So that the grass does not have a chance to get started again, leave the mulch and mature legume vines in place throughout the dry season until it’s time to prepare the land for next season’s crops. By that time, there won’t be any living grass roots down in the soil and you will have successfully killed off your enemy, the grass with the running rootstalks.
Before I finish, just one more hint about smothering weeds that have running rootstalks. Klaus Prinz says that he has successfully grown black beans with a crop of maize. He says that these beans make a tight cover over the ground. Because they’re legumes, they add nitrogen to the soil and smother weeds that are hard to control. If you try this, don’t plant the beans at the same time you plant your maize. Wait until after the first weeding of the maize.
Information and some principles relating to this item are in other DCFRN items. You might wish to present some or all of this material with this item. They are:
Weeds – Package 5, Item 1/A
Mulching crops grown on ridges – Package 7, Item 1/D
Nitrogen fertilizer that doesn’t cost any money – Package 5, Item 4
Intercropping – Package 3, Item 6