I believe I remember reading about Dorothy's Johnson grass experiences (at least some of them) in her book. : ) I pull out or dig out all I can. The hand-pulling is really easy with any Johnson grass that has just recently sprouted from seed. With plants sprouting from rhizomes, I have to dig. Then, I crawl on my hands and knees along the rows of corn with my Fiskars garden scissors in my hands about once a week and cut off the Johnson grass as close to the ground as I can. The more you keep the topgrowth clipped back short, the more you weaken it since there aren't any (or many) leaves above ground conducting photosynthesis and sending energy to the plant roots. Johnson grass is and always has been my number one garden problem. I dig out all I can every year, and I rototill the remainder on purpose to break up the rhizomes into a million pieces in winter. If you leave them exposed on the surface of the ground, they can dehydrate and then freeze if the weather is cold enough. I will repeatedly rototill and rake out all the pieces of rhizomes I can find in winter. We are in our 15th year here and I still have Johnson grass issues in the big garden, but probably only about 10% of what I once had. Last Sunday I pulled out seedling Johnson grass from my rows of Silver Queen, Country Gentleman and Early Sunglow Corn. Then I dug out the plants that had come back from rhizomes. This is only our second year to grow corn in this area, and there's not much Johnson Grass at all now compared to last year. However, this is a sandy soil area and I can dig pretty deep and get out a lot of the rhizomes. In our big garden where the soil is mostly clay, it is more of a battle. If you rototilled your soil before planting the corn, you might have Johnson grass seedlings that sprouted from seed in the soil. It would take a while, but you could dig themout. If you rototilled or plowed and broke up existing Johnson Grass rhizomes into billions of smaller pieces, and then you didn't rake them out, then there isn't much you can do except cut them off to keep them short so they will weaken. It is easier to tell the corn from the Johnson grass once they are 6-8" tall. Before we moved here, I thought bermuda grass was the worst stuff on earth after battling to keep it out of garden beds in Fort Worth. After moving here, I quickly learned that bermuda grass is a lazy wimp compared to Johnson grass. Johnson grass is bermuda grass on steroids. Eventually the corn gets tall enough and casts enough shade that it will outcompete the Johnson grass but you can help ensure that by cutting back the Johnson grass. If you spaced your corn plants really widely apart, you can use a string trimmer to cut only the Johnson grass. You could use a cheap foam paintbrush to brush a grasskiller type herbicide onto the Johnson grass, but don't get it on the corn! Be careful and read the label carefully if you use any of the herbicides mentioned in the link that Scott has in his response. Some herbicides that work on Johnson grass in corn fields only work on popcorn or field corn and will damage or kill Johnson grass. If you had planted Roundup Ready corn (available only to commercial growers as far as I know), you could have sprayed the whole field with Round-up and the corn would have been fine. However, I am not recommending that...just saying that is how commercial growers often do it. Unfortunately, the heavy use of RR corn varieties now has given us Johnson grass in some nations and in some states (including Arkansas) that now is tolerant of glyphosate type herbicides. If you didn't have a crop in the field, regular mowing will get rid of the Johnson grass (same mechanism as allowing goats to graze it---having the top growth removed repeatedly weakens it) but the issue is that you do have a crop in the field. Johnson grass is probably the #1 reason gardeners in my county give up gardening. You see it every year. They decide to have a garden. They plow up the ground or rototill it and immediately plant. They ignore those little grass plants that start sprouting. By June, those little sprouts of Johnson Grass are taller than the rest of the garden, including being taller than the corn and taller than the tomato plants. The gardeners try to pull out the grass and discovers it has rhizomes that run for feet and that are as big around as their index finger. They abandon the garden before the Fourth of July and let the Johnson grass win. They do this for multiple years before deciding that gardening isn't fun. Don't let this happen to you. When a gardener abandons a garden full of Johnson grass, it grows until it sets seed, and then you have to deal with a ton more Johnson Grass next year. With consistent effort, you can get rid of it. Don't let it defeat you. On the other hand, if you are in a rural or semi-rural area where there likely is a raccoon population, and if your garden isn't fenced, just relax. Johnson grass won't be a problem, but the coons will be. They will harvest the corn for you about 3-5 days before it is ready for you to harvest it, and they'll tear up all the cornstalks for you, leaving only the Johnson grass, growing happily and quite healthy. At that point, having lost the corn crop to the coons, you can spray the Johnson grass with a herbicide if you wish, and then plant corn in mid-summer for a fall harvest. Dawn

Johnson grass can be controlled by repeated, diligent removal of above ground plant parts. Details in the link. Glyphosate based herbicides such as Roundup will control Johnson and other perennial rooted grasses effectively, although it may take several applications. Apply glyphosate when Johnsongrass is actively growing and between 12 and 24 inches tall. Of course applications of this material will do nothing to prevent the future re-invasion of these grasses, either by seed or by rhizomes from adjacent weed patches. Glyphosate is not herbicidally active once it hits soil, and it will break down completely over time. Once your target weeds are controlled, make sure to remove any future weed seedlings and apply a protective mulch. Here is a link that might be useful: Attra link

This is a very old post, from 2006, but asks a very common question. Johnson grass is one of the invasive grass species and it spreads as much by the rhizomes as from seed. Covering Johnson grass with light excluding barriers will not stop it just as none of the poisons sold will. The only really effective method of removal is to dig out the clumps and be sure you get all of the rhizome since more will sprout from any wee bit of rhizome left behind, just like Quack grass will.

"You could pen hogs in the area,they root up and eat the roots" LOL! I feel quite sure my neighbors would have plenty to say about that, and none of it would be very nice! " Not sure what you are spraying with but every herbaside I know of states in instructions not to mow shortly before or after spraying." I really do have sense enough to read instructions. I didn't mean I do either one shortly after the other. There is a definite time lapse between the mowing and spraying. " digging these plants out is the only really sure way to eliminate them" I was afraid of that. But you can't blame me for hoping someone just might know of a better herbicide than Round-Up for this purpose. I know it's going to take a lot of time, But I'm hoping that persistence will pay off. . .. .. . Thanks all, for responding! Rusty