Italian Ryegrass Control & Oats

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Nearly all of my knowledge about this topic comes from growers – growers in the United States, the U.K., and Australia. The rest is from academics, and some of my personal experience. But I want to recognize the growers, because I have stolen from them freely.

Italian Ryegrass is an annual grass species native to the Mediterranean, Eastern Europe, North Africa, and Middle East Region. Think of Iran, Iraq, Lebanon, Jordan, Turkey, Bulgaria, Spain, as far north as France, and the North African countries to the south. Everywhere else in the world, Italian Ryegrass has been introduced. It has been introduced into non-native areas as a pasture grass. Ryegrass has a prolific, fibrous root system that germinates and emerges quickly, out-competing other species. And it has good nutritional value for grazing livestock.

The taxonomy that we are used to here in the Inland Northwest is Lolium Multiflorum, and is a diploid in the Poacia family, “However, its tendency to form tetraploids has resulted in the development of a number of high-yielding commercial tetraploid varieties. Multiple introductions and the outcrossing breeding system of L. multiflorum mean that weedy populations can be highly genetically variable.” (Invasive Species Copendium http://www.cabi.org/isc/datasheet/31165)

I have grown both diploid and tetraploid ryegrasses, and tetraploids tend to produce seeds of larger mass. This could be an issue for mechanical means of control, which I will address later. The important thing to recognize as stated in the paragraph above is “that weedy populations can be highly genetically variable.” Recognizing this helps us understand how ryegrass can easily become herbicide resistance.

Further – “The taxonomy and nomenclature of Lolium multiflorum is complicated by the many known variants and forms; var. macrostachyum, var. microstachyum, forma longiaristatum, forma cristatum and forma viviparum were named and briefly described by Beddows (1973). L. multiflorum hybridizes freely with L. perenne (L. x hybridum), L. rigidum (L. x hubbardiid), L. temulentum and L. remotum.” (Invasive Species Copendium)

Not only is ryegrass highly genetically variable, but that is “complicated by the many known variants and forms” of the plant. It hybridizes freely. The point is that while L. multiflorum is used as a common name for the species we are familiar with, other people around the world may be studying basically the same weed while calling it something else. So if you are studying academic literature on how to control ryegrass in cropping systems around the world, you could run into a number of different specie names.

Someone once said that a weed is “a plant out of place.” This definition, like many phrases, can break down if taken too far. But for ryegrass, it is particularly fitting. I grew up on a grass seed farm in Oregon, and our cropping system was virtually 100% annual ryegrass seed production. Linn County, Oregon boasts itself as the “Grass Seed Capital of the World,” and parts of the Willamette Valley have been dominated by annual ryegrass seed production in the last century. We call it a weed in our wheat-dominated cropping system, but there it is a cash crop, produced by the thousands of acres.

Ryegrass seed field in the Willamette Valley, Oregon

Much of the Willamette Valley’s production has historically been sold to large cattle ranches in the Southeast United States, aerially seeded (or otherwise) over large tracts of pasture and grazing ground. In more recent years, a market developed to sell annual ryegrass seed to growers in the Midwest for cover crop in their corn-soybean rotation.

So annual ryegrass is an herbicide-resistant weed in California, a seed crop in Oregon, an herbicide resistant weed in the Inland Northwest, a cover crop in the Midwest, an herbicide resistant weed in the Mississippi Delta in wheat production areas, and a great pasture grass further in the Southeast.

In agro-ecosystems around the world it has been a problematic weed, particularly in the wheat producing regions of Australia. And it is widely recognized as competing with blackgrass in the U.K. as the top most problematic grass weed. In both places it has shown herbicide resistance. There are dozens of academic journal entries and articles from around the world on how to control annual ryegrass in cropping systems. You can put together quite a library.

Taking a step up for a higher look, think about what you learned about crop diseases in Agronomy 101. Plant diseases require: 1. The presence of the pathogen, 2. A susceptible host, and 3. Favorable environmental conditions for disease development.

Weeds really aren’t that different. You have to have the presence of the weed seed, the soil management that has led to the condition that your soil is in as a host, and favorable environmental conditions. With all of the above requirements, farmers need to understand that they are in control of most of these factors.

It is possible that a helicopter could be sent to drop a bucket of annual ryegrass seed onto your field. That would be out of your control. But aside from strange things, if a weed has shown up in your field, you have made it possible.

Jim Cook and Roger Veseth pointed out in their book “Wheat Health Management” the observation that from a pathology point of view, crop rotations should see wheat out of the rotation twice as long as it is in the rotation. From a weed control perspective a similar principle probably applies. Lack of diversity is part of creating the environment and conditions for invasive weeds to thrive.

So if you don’t have ryegrass issues now, the question is: why? What are you doing different than the Australians, than the British, than your neighbors who have ryegrass? If you are doing basically the same crop rotation and weed management system that your neighbors with ryegrass problems do, you are probably a sitting duck. And if your neighbors are doing everything in their power to select for herbicide resistance, the issue doesn’t get any easier.

The big question is: How are you creating a positive or negative environment for invasive ryegrass to thrive?

In order to avoid prolific weed problems, and especially prolific herbicide-resistant weed problems, the approach of “treating the symptoms” can lead to a disastrous dead-end. That’s why herbicide-resistance is the big issue that it is. Band-aids only go so far. If you have herbicide-resistant ryegrass, you do need an all-out war. And if ryegrass continues to spread in our region (and I think it will), and if it continues to show more herbicide-resistance (and I think it will), very creative means of control will have to be employed. Just ask the Australians, where desperation has been the mother of invention.

We’ll ask the Australians, but first let’s look at a couple of parallel examples of where the Band-aid approach is not sustainable.

Rattail Fescue can be controlled at a high rate with some light tillage at the right time of year and right time of growth stage. I have had no-till farmers say to me that the rattail is taking over and they are left with no other option but to rotate the light tillage over the farm. I say – OK – run the light tillage over the farm and take care of the rattail problem. And let’s say you get 100% control of the rattail fescue. The question then becomes: What are you going to do to prevent the rattail fescue problem from coming back. Once upon a time the rattail fescue wasn’t there, but the farmer created the condition for it to come in and spread. If rotation and weed management practices aren’t changed, the conditions for thriving rattail fescue stay the same, and then the light tillage will be called up again.

Another parallel issue is the matter of pH’s lowering on farms in our region, and lime is being bought and applied. A number of extension studies and academic focus has been on liming rates. OK – open the checkbook, spread the lime, fix the pH. But the pH’s will lower again if the conditions that caused the lowering stay the same. The checkbook will get opened again in a couple of years. Band-aids aren’t the answer to this or to annual ryegrass weed control.

Annual ryegrass is a fantastic multiplier. Five plants/m² causes 5% yield loss in cereals. Ryegrass tillers profusely, and each plant commonly produces over 20 heads and 5,000 seeds. All of this is from AHDB, https://cereals.ahdb.org.uk/media/1184357/Effective-sustainable-Italian-rye-grass-control-in-winter-cereals.pdf

Again, the genetic variability and adaptability and prolific seed production make for a perfect storm for a wide-spreading, herbicide-resistant weed.

Italian ryegrass infestation in wheat crop

Ten years ago or so we heard doomsday reports of jointed goatgrass and its potential to destroy wheat production as we know it in the Inland Northwest. While it is still a problem with some resistance, it was avoided in large part through sanitation measures with non-selective herbicides and Clearfield technology (though it is now showing signs of being tolerant to Beyond). Ryegrass will probably not be such a simple cure. I do not hear growers too worried about jointed goatgrass, but I do hear them extremely worried about annual ryegrass. And based upon the experiences around the world in trying to control annual ryegrass, I think the worry is very much justified.

Australia has what they call the “Big 6” means of controlling herbicide resistant weeds, and you have to pick at least 3 of the 6. The Big 6 are: 1. Diverse Rotations, 2. Double Knock, 3. Mix & Rotate, 4. Crop Competition, 5. Stop Weed Seed Set, 6. Harvest Weed Seed Control. I am going to go through these six strategies, but not in that order.

Rotating herbicides with different modes of action is recommended, and it is a common-sense good recommendation. There are reports of Australian researchers breeding herbicide-resistance to some modes of action in annual ryegrass in as early as three generations. ALS inhibiting herbicides, ACCase inhibiting herbicides, and glyphosate – Italian ryegrass is finding resistance to all of the above in Australia. Once you have resistance to those three modes of action in a predominantly cereal producing region, you are screwed. There is just no nicer way to put it.

From an herbicide control perspective, and for an all-out war to eradicate the problem, the Australians suggest a “Double Knock”: perform a burndown with glyphosate, then follow several days later with Paraquat or a Paraquat/Diquat mix. This might work especially well in a delayed seeding scenario, or just prior to establishing a warm season crop.

AHDB recommends flufenacet + pendimethalin or thiocarbonate applied pre-emergence, and iodosulfuron + mesosulfuron or pinoxaden applied post-emergence. They note, however, that “there is a high risk with both post-emergence options that herbice resistance may develop.” This strategy is not wholly different from standard practice here.

We have been battling annual ryegrass and other grassy weeds with the best weed control maintenance that we can, but the maintenance routine has not worked well with annual ryegrass, and resistance has shown that. The Australian “Double Knock” gets you out of the routine and tries to annihilate the ryegrass. It is like the difference between storming the beach with troop after troop, many of which get shot down as they are storming, and dropping an atomic bomb. The maintenance routine will probably lead to more resistance.

Herbicides are a useful tool if they can be effectively used to eradicate weeds. But like Jesus said – He who lives by the sword dies by the sword. He who lives by glyphosate dies by glyphosate. The same tool used for eradication can be the tool that allows for herbicide-resistance selection, especially if it is used consistently, regularly, and in maintenance mode.

No new modes of action have been released in recent years as tools for growers, and nothing really new is coming down the pipeline. There may be new compound formulations, but no new modes of action. With the majority of U.S. acres in Roundup Ready corn and soybeans, the incentive hasn’t been there to develop new modes of action. Chemical companies and other researchers are focusing more on the weed seed bank rather than killing the plants themselves. Research and development is being done on root exudates and biological control of weed seeds in the soil.

Harvest Weed Seed Control deals with mechanical means to deal with weed seeds coming through the combine. This is where desperation has been the mother of invention in Australia, and most if not all of these inventions have come from growers.

Narrow Windrow Burning. Narrow windrows with straw and chaff, including weed seeds, are deposited out of the back of the combine and then burnt later. This can be effective, but at the cost of messing up the carbon cycle of the field, and isn’t legal in many places.

Chaff Lining. The process creates a separate stream for chaff on the combine, apart from straw, that includes the weed seeds. Italian ryegrass is relatively light seed, approximately 26 lb./bu. The line deposits the chaff into lines behind the combine, not allowing weed seeds to get good contact with the soil. If a rain comes, the germinated weed seed does not survive long.

Chaff Decks. This is similar to the chaff lining as a chaff line is created on the combine, but the lines deposit the chaff onto the combine tire tracks. This system is designed for controlled traffic so that weed seeds are limited to specific tramlines. It makes identification and control of the weeds concentrated and more manageable.

Direct Baling: One farmer described the process to me this way – “It is where you pull the 2nd most unreliable piece of equipment on the farm behind the #1 most unreliable piece of equipment on the farm, and then hope for the best.” The combine pulls a baler, where bales are deposited in the field and taken off later. I think this is a poor idea for a couple of reasons. There is a high cost to exporting carbon and other plant nutrients from the field, and there is no guarantee that the weed seed will not escape. Bales could be loaded up on an un-tarped truck, hauled down the highway to the biochar plant or feedlot, and then broadcast along the highway as it moves at 55 mph. There is no guarantee that it will not escape a feedlot once it gets there.

Chaff Carts. A combine pulls a cart that collects all of the chaff and weed seed, and then the farmer burns the chaff later. Maybe the farmer can figure out how to heat the shop during the winter this way. This may have good results, but it is inconvenient to pull a cart behind a combine.

Cage Mills. A combine pulls roller mills, where the chaff and weed seeds are run through and obliterated. There is high rate of control when it works properly, but the equipment is expensive and inconvenient.

There are challenges to controlling weed seed at harvest, the main one being that you have to get the weed seeds into the combine. Some weed seeds may be too green, or they already dropped their seed, or you’re not cutting low enough to pickup the mature weed seeds heads. Some Australian growers have had better luck with stripper headers. These challenges emphasize why it’s important to pick at least 3 of the 6 control methods, rather than putting all eggs into one basket.

Annual ryegrass

Tillage is another mechanical means of control. Fall tillage can be effective in killing newly emerged ryegrass, but besides all of the negative things this does to soil structure and biology, you are probably opening a can of worms in exposing more weed seed. Spring tillage is an even worse idea. More mature ryegrass plants will require several passes to separate soil from roots, plus you are exposing more weed seed. I have burned a field, plowed it, disked it, harrowed it, and watched a green, fuzzy volunteer crop of ryegrass appear. If there are viable seeds in the ground, tillage will help propagate them. Studies show that Italian ryegrass seed stays viable in soils for up to about 5 years.

More narrow seed rows appear to also be helping with competition, and some growers have gone down to 7 inch spacing.

Stopping weed seed set is probably the most underrated and effective means of control. Many growers are looking to integrate livestock into their cropping systems for “soil health” reasons. And a lot of those reasons are good. Having this option is a luxury, but integrating livestock could prove necessary to control herbicide-resistant weeds like ryegrass. Ryegrass is not yet resistant to sheep and cattle. Replacing a cash crop with a grazing crop will significantly help weed seed set, and both sheep and cattle target ryegrass for its nutrition. It is possible that to get control this way a multi-year approach should be taken. It is possible for grazed ryegrass crowns to green up in the fall. That is not how annuals typically work, but you never know. Hay crops are another option, but as stated earlier, it is better to leave the carbon in the field.

One Australian farmer told me that despite diverse crop rotation and no-tillage for 20 or 30 years, he was still having ryegrass problems. Diverse rotations and no-till are not an end in themselves. It wasn’t until he integrated livestock (in his case sheep) that he was able to significantly reduce ryegrass populations on the farm. Again – pick at least 3 of the 6.

We came up with some anecdotal evidence that led us to believe that oats provide significant success as a rotational control of Italian ryegrass, and also seemed to discourage wireworm damage. We saw this at field scale as we were trying to develop a market for Shepherd’s Grain branded oatmeal. We had several growers put in fields of milling quality oats for this project, however all the fields did not make high enough test weight for milling. We were left selling 32 lb./bu. oats (which were basically straw) into the feed market.

As part of an effort to establish the market, over the last few years we have been doing variety, fertility, and seeding rate trials with milling oat varieties. The aim was to overcome the issue of producing low test weight oats. We identified a small handful of varieties that appear to do well on the Palouse in terms of yield and test weight.

Milling oats require 38 lb. test weight. Under 38 lb. will be docked. Under 36 lb. will be rejected by the mills.

Establishing viable markets for alternative crops that are necessary means of controlling issues like ryegrass is a big challenge here and across the world where infrastructure and farm markets are set up for monocultures.

After having narrowed down the varieties we think are most successful for the Palouse, we turned our attention back to researching the association of Italian ryegrass to oats. Last year we compared ryegrass populations in oats vs. spring wheat in the same field. We also want to chase the anecdotal evidence we saw with wireworm control.

We set up strip trials of oats next to strip trials of spring oats in a field with large populations of Italian ryegrass. We canvassed the strips to get weed counts and density. The pictures below show that Italian ryegrass was healthier in the spring wheat compared to the oats. The question is why. We plan to do more testing in the future to see if the results are due to oats out-competing the ryegrass, or if there is some allelopathic association as the cause.