Outsmarting Quackgrass

Quackgrass shoots and rhizomes. Silver dot is a quarter for size reference.

Quackgrass, Elymus repens (L.) Gould, is a major problem in cropping systems across the United States and Canada. It is a persistent, perennial, cool-season weedy grass that has the unique ability to hide below the surface and suddenly invade an area. When you least expect it, quackgrass can shoot its leaf blades, spreading its durable rhizomes into a thick mat.

Once quackgrass invades, you will have no choice but to address it. According Penn State Extension Dwight Lingenfelter and William Curran, authors of the bulletin Quackgrass Management, an Integrated Approach, “This competitive perennial grass can reduce crop yields up to 95 percent.” And… “Once introduced into a field, quackgrass is nearly impossible to eradicate.”

First and foremost advice for anyone assessing, preparing or managing land for a cropping enterprise: Know quackgrass.  And don’t get discouraged, because you can overcome it.  Read on for recommended land preparation and management practices.

It behooves you to virtually eliminate this weed before it surprises the heck out of you, before you’ve already established your crop, before it’s too late or before it can ever gain a foothold.  Taking a small amount of time now to try to i.d. this grass and educate yourself about its control might save you eons of frustration down the road.  On the other hand if you have no suspicions, quackgrass will sneak up on you like a pack of wolves on a rabbit in the middle of a clearing.

Here are the basic identification characteristics:

1. Quack has “auricles” or small protrusions of lighter color where the leaf blades meet and clasp the stem.

2. Many grasses resemble the appearance of quackgrass above ground,so the easiest way to confirm quackgrass is by its rhizome. Rhizomes are thick 1/8” diameter roots spread laterally. They have nodes every couple inches that send of short feeder roots. Each node on a rhizome is also a potential point to shoot a new set of leaf blades. Quackgrass rhizomes love the 3”-6” deep zone. Older rhizomes are browner in color, and newer rhizomes are bright whitish in color with a smooth gloss. Rhizomes drill through the soil (and virtually anything else) by virtue of their pin-sharp tips.

3. Quackgrass seed heads form later in the season, are about 2-8 inches long with two distinct rows of seeds.

What makes this weed so difficult to control?
It is remarkable how widespread this weed is. Here are some reasons for the success it has had over the centuries on our farms and in our fields across the nation.

• Quackgrass is persistent. Rhizomes stay viable buried in undisturbed soil. Rhizomes lay dormant below the surface, making them very hard to detect and very hard to reach with surface cultivation or herbicides.

• Quackgrass is smart. When it knows you’re there, it hides. When it sees you leave the field it decides to shoot its leaf blades above ground, send its rhizomes into a lateral mat and take over an area. Note: Quackgrass’ ability to conduct a stakeout of your farm is not research based, but it’s a good hypothesis!  Also note, you are smarter than a weeds.  (If you keep reading.)

• Quackgrass is opportunistic. It is the first to take over disturbed soil and is very talented at doing this.  It is as if this is one of it’s key evolutionary traits, enabling it to outcompete other weeds by being the quickest to invade an area.

• Quackgrass multiplies like there is no tomorrow. It multiplies sexually by producing seed, and asexually by producing more rhizomes and shoots.

• Quackgrass feels no pain. Mow the grass, it shoots right up again (although theoretically when mowed very low it will have less vigor, a key concept we’ll explore in a minute) Cut the rhizome, it shoots right up again. Cut the rhizome and in fact you’ve just multiplied the plant. (Although in some cases it’s easier to combat smaller plants than larger ones, again, a concept we’ll get into shortly)

• Quackgrass is adaptable. It grows from the deep south to the far north. Quackgrass will tolerate very alkaline and very acidic soils, although its growth will slow the farther the soil pH strays from neutral 7. Generally it tolerates poor, compacted soils. Sounds like a weed, don’t it?

• Quackgrass is mean. According to some studies it has allelopathic potential or the potential to release compounds into the soil that inhibit other plant growth. It also will mine a soil very quickly, making nutrients and water unavailable for crop uptake. Quack likes the weather to be cool and moist.  On the contrary, most of your crops like the weather on the warmer side. This gives quack its advantage, with leaf blades very quickly reaching a height that smothers low or slow growing crops.

• Quackgrass is cool and cunning. It takes refuge underneath the cover of other plants or ground covers, which provide the cool, moist microclimate that it likes. Studies have found that quackgrass emergence can be higher in fields that had been previously cover cropped than in fields that had been previously fallowed. Most mulches provide cool soil underneath that keeps quackgrass rhizomes happy. Compared to a spot with no mulch, quackgrass will likely have a more fortified root system below a mulch cover, giving it the vigor it needs to push its leaf blades above the cover with ease.

What to do, what to do?

Quackgrass might seem like a superweed but don’t worry.  It has an achilles heel.  From here on this article will branch out from one very simple concept, the essential secret to controlling quackgrass. To summarize, there are a finite amount of sugar or energy stores in every quackgrass rhizome. Every time a rhizome shoots a leaf blade, it depletes some of its energy. The plant will not reach sufficient photosynthetic capacity to replace rhizome energy stores until there are three or four new leaves. Thus if the plant is allowed to shoot but tilled or mowed before it reaches three or four leaves, rhizome energy stores are at a net loss. If this process is repeated— letting it shoot leaves and knocking the plant back down – then eventually all energy stores in the rhizome become depleted and sianara quackgrass.

There is a publication by Heather Westwood, Kara Cox and Eric Gallandt from University of Maine Sustainable Agriculture Program, “Quackgrass Management on Organic Farms,” that elaborates on the above secrets beautifully. The 5-page publication provides an excellent overview of quackgrass management.

The above concept is the key to successful quackgrass control, whether it be organically or with chemical control. Quackgrass is smart but we are smarter. Just don’t let that quackgrass overhear you. Shhhhhhhhhh, wisper our secret… “We trick quack into thinking conditions are right for shooting leaves – we entice it and invite it to shoot, and then we knock it right back down again.  Remember that opportunistic evolutionary trait? — Where quackgrass rhizomes are activated when soil is disturbed?  We use this to our advantage.  For quack is stubborn when it comes to shooting new leaves from those little rhizomes, despite how depleted energy stores might be. Once we disturb the plant by chopping, cultivating, harrowing, etc., the plant keeps shooting again and again, never knowing that we’ll be plotting our next attack, knocking it back down again and again until it’s eventually down for the count!”

Sounds like a lot of work and excessive, repeated tillage, mowing or cultivation, but these methods are some of the only few proven to work.

3-pt hitch tillers are good for cultivating wide swaths or walk-behinds like the one pictured are good for tilling narrow weed-free strips beside crop rows. Models with forward rotating tines are good for shallow, repeated cultivation. Models with counter or reverse rotating tines are good for deeper tillage for tilling quackgrass the first couple passes.

Tine cultivators brought in before grass blades grow too high can knock down quackgrass and also bring rhizomes to the surface to dry out.

Rototilling works for knocking recently emerged shoots back down, but there is a danger that once rhizomes are chopped there is a chance for more multiplication of the weed. You need to stay faithful with a repeated tillage regime if you are using a rototiller. Same goes for other types of cultivation, but “S” or “C” tine tillers and cultivators will be more effective in bringing quackgrass rhizomes to the surface, achieving the double whammy of knocking back recently emerged shoots and bringing rhizomes to the surface where they desiccate and die.

Mulch or plant canopy cover, as discussed above, can be a dangerous proposition because of the cool, moist microclimate that quackgrass rhizomes love. Mulch needs to be deep, and I mean very deep. Permeable mulch such as wood chips or straw laid very thick might not smother the weed, but it will force the plant to deplete more energy reserves to push leaf blades through the cover to sunlight.  This tires out the weed somewhat.  Weeding out quackgrass from mulch or mulch-softened soil is usually much easier – you can pull out whole rhizomes — than weeding out from bare compacted soil, where it is nearly impossible to extricate all the rhizome.

Ripping out weed fabric that has been overgrown with quackgrass. The weed has shot its rhizomes through the fabric and becomes almost impossible to separate. Once quack rhizomes are woven through, the weed fabric becomes practically useless. Keeping the surface of the weed fabric free from any leaf litter or other decomposing debris helps avoid this problem.

Be careful about using synthetic mulches like weed fabric that you might think are impermeable to weeds. Quackgrass roots will poke right through them. Synthetic covers like landscape fabric can work as long as they are laid lightly on top of the surface. Quackgrass rhizomes can not weave through loosely laid fabric media because they lack the firmness they need for poking through. Never cover a weed fabric with more natural mulch or else quack will not only poke through, but also establish a mat on top of your weed fabric within the decomposing mulch.

One farmer I know has had success smothering quackgrass with weed fabric, but he lays it lightly with fabric staples, never loads anything on top and removes it or changes it around frequently enough to never let weedy grasses intermingle with the fabric and establish a foothold.

Any forked tool is a handy tool to have around for more delicate eradication of quackgrass around perennials or in close proximity to crop plants.  Tools like pitchforks or fork hoes can bring rhizomes to the surface without breaking them, making for thorough eradication. May the fork be with you.

The Chillington fork hoe. 7″ prongs are perfect for uprooting quackgrass rhizomes. Long handle is ergonomic. All weeding can be done from a standing up position. Once the tool pulls out rhizomes, they can be laid out to dry in the sun or gathered to be disposed of and never to return.

When hand weeding quackgrass, pull firm but pull slowly, the goal always being to pull out as much rhizome as possible. They should pull out like strands of spaghetti if you’re good at it.

Glyphosate-based herbicides (e.g. Roundup) are suggested for chemical control. But application rates need to be adjusted to account for the need to access the crown and rhizome of the plant. See this short video for a quick summary. Glufosinate-ammonium-based herbicides (e.g., Finale) is another approach. Careful with either of these approaches as these herbicides are non-selective and they will injure the plants you want to protect as well as the ones you wish to eradicate. Contact your local agricultural Extension service for more ideas on selective herbicides that provide protection for the crop you are growing.

It is much easier to eradicate quackgrass from a field before you plant a crop, so be patient and leave yourself an extra year in your crop rotation or soil conditioning phase to practice a repeated tillage fallow. Short season cover crops like buckwheat can be planted in between the times you till. Pigs can be rotated in, they are excellent tillage machines, stomping out quackgrass and even eating it when they are trained to do so.

In closing, a weed is only a plant growing in the wrong place right? Quackgrass has a nice place in pastures, with an average value as a forage for grazing livestock. It is an excellent erosion control, lavishing at the opportunity to take over and stabilize any disturbed soil no matter what the slope. And I haven’t tried this yet, but in case you find yourself a bit sweaty and stinky coming in from the field from battling all that quackgrass, apparently you can burn the rhizomes as incense.