Organic control of Johnsongrass

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Will Glazik asked 4 months ago

My name is Will Glazik and I’m working with a group of farmers known as the IDEA Farm Network.  One of the farmers in the group is in southern Indiana and is having trouble controlling Johnsongrass in organic row crops.  Would anyone have some ideas for control strategies? 
Thank you for your help

3 Answers
Adam Davis answered 4 months ago

Managing perennial weeds that grow from both rhizomes (underground, energy-rich stems) and seeds, such as Johnsongrass or Canada thistle requires a long-term strategy consisting of several components: 1) identifying patches as early as possible and preventing spread; 2) depleting the weeds’ energy reserves; and 3) removing rhizomes.

  1. Identification and containment. When patches are identified, they should be flagged and managed separately during tillage operations (if possible, avoid tillage and spot treat with a perennial forage in a bad patch) to avoid spreading rhizomes throughout the field. Running through a Johnsongrass patch with a disk and continuing on into the rest of the field will sever the rhizomes into small pieces and make the patch expand rapidly. To avoid spreading rhizomes from field to field, make sure that you clean cultivation equipment after working an area that has the perennial weed in it.
  2. Deplete energy reserves. Perennial weeds store energy in underground perennating organs (rhizomes for Johnsongrass, quackgrass and Canada thistle; nutlets or corms for nutsedge). They spend a large amount of this energy in producing new top growth in the spring, and especialy on making flowering heads. This is the time of year when you want to hit them hard. Treat the perennial weed patch with a short-cycle, high biomass, warm season cover crop like sorghum sudangrass, and repeat the following steps: 1) allow cover to grow, 2) watch for seedhead production by weed, 3) mow off. The weed will keep trying to produce flowering buds, and this will drain the energy from the perennating organs. This will not kill the patch immediately, but fewer plants will overwinter, and repeating this strategy in the following year should finish it off. For small patches, placing an opaque tarp over the plants can prevent photosynthesis and deplete their reserves that way. If you have very hot summer temperatures, you can also solarize small patches with clear plastic, killing the weeds with heat.
  3. Removing rhizomes (optional, and tricky): For those who have access to cultivation equipment with both shanks and sweeps, like the Danish S-tine cultivator setup, you can use a rig like this to bring rhizomes to the surface, where they’ll dry out. Following this with a spike-tooth harrow can drag the rhizomes out of the field.

For resources in the scientific literature on managing perennial weeds, see:
A. J. Bicksler, J. Masiunas and A. S. Davis. 2012. Canada thistle (Cirsium arvense) suppression by sudangrass interference and defoliation. Weed Science. 60: 260-266.
McWhorter CG, History, biology, and control of johnsongrass. Rev Weed Sci  4: 85-121 (1989).

Bill Curran answered 4 months ago

I agree with Adam.  Really takes an integrated approach to manage a problem perennial in organic.  You can suppress it with tillage, but if you want to really reduce the amount of time and effort you have to expend, you need to really think about the rotation and focus on cultural and mechanical control tactics.  For Johnsongrass, growing a competitive crop, frequent mowing, deep tillage followed by a competitive crop, grazing, etc.  Corn and soybean are tough.  Alfalfa is a great crop as Johnsongrass doesn’t usually tolerate mowing every 30 to 35 days.  The Bickler et al article on Canada thistle is a good one.  I also like the Randy Anderson article on Canada thistle (  it can be related to other herbaceous problem perennials.

Adam Davis answered 4 months ago

Here is additional information on controlling perennial weeds in organic systems from two Illinois organic growers:
From Dave Bishop (MOSES Farmer of the Year):
We hosted a U of I experiment some years ago using a specific variety of Sudan Grass to smother Canadian Thistle.  Worked very well!
From Dave Campbell (Lily Lake Organic Farms, MOSES Board):
The link listed below was research that was funded by NCR-SARE almost 10 years ago I think while I was serving on the NCR-SARE Council. I had also served as a farmer advisor and had the opportunity to visit some of our farmer research plots with Dan Anderson on this project.  Before this research project was submitted for approval we had compared sorghum/sudangrass with a couple of other weed suppressing options on my farm for a research project with the New Ag Network a year prior to pre-approval  of this SARE funded grant.  S/sudangrass  was by far the most effective.  Since you probably won’t have much success contacting John M., Abram B., or Dan A. I would suggest running your thoughts by Dr. Adam Davis given his close proximity to you and more so his expertise in weed research with ARS.
S/sudangrass is very effective because the grass grows very fast and produces much biomass.  The canada thistle, (ct), cannot compete well given that sunlight is typically very minimal down at the level of the ct and so very little photosynthesis is taking place with the ct, thereby weakening the root reserves.  Also, much biomass from the roots of the s/sudangrass also competes with the ct, and thereby also weakening root reserves.  Probably safe to assume that in a dry late summer period the ct roots will struggle even more to survive.
The downside to using s/s grass is that you will have an entire year where you will have no cash crop income.  You may want to plant s/sgrass only where you feel as though the ct pressure is really strong or possibly in sections of your field/s where the problem is worse if that option is practical.  Timing of planting of s/sgrass is important.  I would check with Adam to see when is the ideal time to sow s/sgrass in your area.  I sowed s/sgrass on June 11th back in 2010 and had very good success at my far northern IL. location.  Don’t expect 100% erradication of ct although you should be able to set ct back quite a bit for a number of years.  The areas of your field where you will most likely see thistle coming back sooner would be along grass waterways because of course you can’t till those spots.  You will also most likely see ct show up initially in fencerows for the same reason.  Obviously you won’t be able to till those areas and so expect some ct in your fields bordering those grass areas.  Also expect some ct to show up on the extreme edges of your field given the fact that there will be more sunlight penetration in those areas, probably more so of course on the south edge of your field.  Nonetheless, using s/sgrass has been proven to work and may be the best option for an organic cash grain rotation.
For cultivating quackgrass:
You can purchase field cultivator double points, (quack points), through Shoup Mfg.  These are listed on page 89 of their Spring catalog.  They will cost about $11 each and they are reversible.  You may want to check with Shoup to see if these will work on your field cultivator before you purchase.  I use them on my IH #45 field cultivator and am very pleased with them.
Also, I use two, #45 field cultivators.  One with wide sweeps I use primarily for my last pass before planting in order to tear out more weeds and the other one is my field cultivator with the quack digger points.  These points are only 2″ wide, (not counting the small flare near the end of the point).  I have very little quack on my farm but I still like using my quack digger during my first pass on ground that was chisel plowed the previous Fall.  This is typically the previous year’s small grain ground that had a red clover cover crop chisel plowed the Fall before.  I also use my quack digger on corn ground that was chisel plowed the previous Fall.  Using the narrow points is my preference for earlier Spring tillage work given that there will be less slabs generated, due to a much narrower sweep on my heavier clay soils given my northeast IL. location. My goal is for the least amount of disturbance as possible to the soil, especially in the early Spring when the soil is still cool and damp/wet.  The narrow shanks still do an excellent job of moving soil as well as mixing residue.