Ok-Hicks,

Most years I don't grow corn, so I might not be the best one to answer your question. But, I did a quick search and found some info. from the University Missouri Extension. The website link is below.

Here is a link that might be useful: University Missouri Extension - Johnsongrass Control

I did not know that Johnsongrass was not native until just now. It was everywhere at the place I grew up. It's a pain in the rear for me now.

Ok-Hicks, I can tell you what not to do with Johnson grass. When I was new to Ok the first spring, I saw a clump of grass no more than a foot tall. It had just rained so I thought I could pull it up. As I was steadily pulling on it, I felt something give way in the middle of my back. When the increasing pain forced me to visit a chiropractor for the first time in my life, he told me I'd pulled the rib head away from the backbone. I didn't know the stuff was perrenial with roots that went five feet into the ground. Unless you bought Roundup Ready corn you don't dare spray...hope you wouldn't anyway so close to corn. But for this year I would find those corn rows and mow the Johnsongrass between them. That's your only chance to get a crop this year. If you study the plants carefully you will learn to tell the difference between corn and Johnson grass plants. Mow it, weedeat it, cut it, lay weedmatting on it--just for the season. And then get a goat; they will eventually kill it through close grazing, but you have to be careful, because in hot dry weather it can kill them. It develops cyanide.

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