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Targeting Weed Seeds at Harvest
As herbicide-resistant weeds become more common across the country, researchers and growers are looking for other ways to control weeds.
In Colorado, they’re looking to techniques and technology developed in Australia, which has significant issues with herbicide-resistant weeds.
Known as harvest weed-seed control, these IPM-friendly methods are designed to destroy or remove weed seeds during harvest to prevent them from raining down onto the soil and replenishing the weed seed bank. In Colorado wheat, weed species of concern are winter annual grasses that share the grain’s growing cycle, like jointed goatgrass, feral rye and downy brome.
“In harvest weed-seed control, the objective is to prevent those seed-bank increases,” explained Colorado State University doctoral candidate Neeta Soni. “There are a number of ways to do it, and we’re investigating to see if they could be adopted in Colorado.”
One way to destroy the weeds seeds is by directing chaff during harvest into a cage mill – imagine a giant coffee grinder – and pulverizing the chaff and weed seeds into powder. That’s the idea behind an Australian innovation known as the Harrington Seed Destructor (and a new competitor called the Seed Terminator).
Another option is to use a piece of equipment called a chaff deck to gather chaff into mounded strips behind the harvester, capturing the weed seed in those mounds of chaff. In some places those chaff strips can be burned, and in others they’re left alone to allow the weed seeds to decay without entering the soil.
A third option is to use chaff carts and collect all the chaff and captured weed seeds for off-site destruction.
“Our research is focused on finding out if there is potential to use these methods in Colorado,” explained Soni, a graduate student of assistant professor Todd Gaines. “So what we needed to know is whether, at harvest, the majority of the winter annual grass seeds are retained in the upper wheat canopy, where they would be vulnerable to the seed destructor or other methods.”
If the weed seeds have already shattered and fallen to the soil, or if the weed seeds are below the cutting height of the combine, the methods would not be as effective.
So the Weed Research Lab team measured and counted a lot of weeds.
“What we found is that the majority of seeds are still retained at harvest,” Soni said. “Downy brome is the same height as wheat, rye is taller and jointed goatgrass a little shorter, but growers could adjust their cut height to manage it.”
Soni then counted out 1,000 seeds of each weed species into a specified amount of chaff and drove to the University of Arkansas where they have a seed destructor set up on a test platform. She ran each bundle through the destructor. The pulverized material was dusted across beds of soil to see if any weed seeds germinated. Virtually none did.
“The seed destructor was 98 percent effective on downy brome and jointed goatgrass, and 99 percent effective on feral rye,” Soni said.
The Gaines lab hopes to conduct field trials with the equipment. They will also study if the strips of mounded chaff are effective in Colorado, or if the state’s dry and windy conditions enable weed seeds to survive and spread.
The seed destructor isn’t commercially available in the United States yet, but a number of researchers are testing versions in different regions and in different crops. The initial model was a tow-behind trailer, but both Australian manufacturers now offer the technology integrated into a combine harvester that retails between $120,000 and $160,000 Australian dollars.
Not every grower would need to buy one.
“It is very common that growers here have their harvesting done by a contractor,” Soni said, “so this could be an extra service they provide.”
But not at every harvest. Because whatever specific iteration of harvest weed-seed control Colorado growers may eventually adopt, it should be just one element of an integrated management strategy, Soni cautioned.
“Repeated use could lead to the selection of earlier-shattering weed seeds, or shorter weeds,” she said. “It has to be used in rotation with other integrated measures, including herbicides and crop rotation.”
In short, it should be part of an IPM program.
Weeds That Look Like Wheat in Lawns
What image comes to mind when you hear the word “wheat”? For me, it’s The Gladiator movie as Maximus runs his hand through the wheat fields on his return home. Epically cool in the movie, not so cool when it’s happening in your front yard. Especially when you learn that this is probably not even true wheat, but weeds that look like wheat, and often with detrimental side effects to your lawn.
Most Common Weeds That Look Like Wheat
When you think of a weed that looks like wheat, it usually means that it has grassy leaves with an inflorescence or spiked seed head, and that is most probably the part of the plant that you are associating with wheat. Common examples are Foxtail grasses, Wild barley, Couch grass, Fingergrass, and Barnyard grass.
A Closer Look At Lawn Weeds That Look Like Wheat
Unfortunately, these next few copycat species that look a lot like wheat, are mostly invasive and can crowd out and suffocate your lawn grass. Although these look like they are meant to be growing in your garden at first glance, they are actually detrimental to your lawn’s overall health.
1) Giant Foxtail (Setaria faberi)
Giant Foxtail is characterized by leaves that have hairs on their upper surface but nothing on the leaf sheath. Its inflorescence is a fuzzy panicle resembling a foxtail, hence the name, that is held up on a smooth erect stem. This plant can reach 16 inches in overall height.
It is an invasive summer annual with a clump-forming growth habit. Originally from Asia and mistakenly introduced to America in the 1920s when it was mixed in with other food grain crops, it thrives in fertile soil. Other similar varieties are Foxtail millet, yellow foxtail, and green foxtail.
2) Wild Barley (Hordeum spontaneum)
Wild barley is an annual that grows throughout winter and seeds in spring. If you can identify it and keep it mowed short it won’t become a recurring problem as it has a quick life cycle and can be cut consistently to prevent it from forming seeds. The long ”hairs” on the seedheads can cause irritation to animals’ eyes, skin, gums and get tangled in their coats, so this is not a pet-friendly weed to have growing in your yard.
3) Quackgrass/Couch grass (Elytrigia repens)
Quackgrass is a cold-season invasive perennial. It has rhizomes that spread underground and can split into separate clumps. This means it spreads fast and is very hard to get rid of.
If you notice fast-growing clumps standing taller than your lawn, investigate the possibility of quackgrass. To positively identify it, look at the base of its stem, where the leaf starts, for two clasping finger-like projections that can be found, called auricles. Other than suffocating your beautiful lawn it does not pose a health risk to either you or your pets.
4) Feather Finger Grass (Chloris virgata)
Generally accepted to be native to America, it easily establishes itself as a weed in areas where it is not necessarily welcome. It aggressively invades bare and disturbed patches of ground and spreads easily along roadsides. It is a common weed in cultivated crops such as alfalfa, maize, and sorghum.
5) Barnyard Grass or Junglerice (Echinochloa colona)
Originally from Asia, this annual invasive grass has distinctive reddish-purple stalks bearing seed heads at the top. It grows by branching out from its base. It can commonly be found in grain crops, gardens, waterways, roadsides, or any other area when it can sneak in and establish itself. The grass’s upright panicles are green, often with a purple tinge, and the tip bends over when mature. Neatly 4-rowed racemes are characteristic.
It is found growing predominantly in damp, fertile soils and can withstand seasonal flooding. It grows in more tropical climates such as South Florida, Texas, and in South-Eastern California. The grass begins flowering at 3-4 weeks and reaches 2m in height, so don’t blink or it will be taking over your yard.
So What Problems Can Grassy Weeds Cause?
I am sure that many of you have seen these weeds growing in your lawn and wondered: Why not just leave them? Is this really something that should be causing me to panic?
They generally grow taller than grasses that have been specifically chosen as a lawn grass. This means your lawn will end up with uneven tuffs that need to be mowed more regularly. They are also typically hairy and have rough seed heads, getting caught in pets’ fur, causing skin irritation, and generally just not resulting in a lush, soft lawn that you want to walk over barefoot (there’s truly no better feeling than this!).
Anything you use to kill grassy weeds will generally kill your lawn too. This makes getting rid of this particular weed type that much harder. You should either spray them with a post-emergent weedicide or pull them out, making sure you get all the roots too. The best method for application would be spot treatment with a paintbrush or an accurate jet spray, as you don’t want to kill your lawn grass with any weedicide drift.
Some Lawn Grasses Have a Wheat-Like Appearance Too
Some lawn grasses form wheat-like seed heads too and they aren’t bad news at all. Examples include Perennial ryegrass, Tall Fescue, and Kentucky Bluegrass. They are all cool-season perennial types of grass that originated from Europe and North Asia.
They are commonly used as turf grasses all year round in the cooler northern states, or as winter cover in the warmer southern states. These grasses are usually seeded over summer grasses, like Bermuda, which goes dormant in winter. This keeps the lawn looking green through the cooler winter months.
When they go to seed they have an erect panicle seed head, and although they are much smaller than those of wheat, there are similarities in their formation. Most people keep their lawns nice and short with regular mowing and so you may never notice the grass forming tiny wheat-like seed heads. But don’t be alarmed if you miss a few mowing sessions, let your lawn grow longer and seed these seed heads. It’s not a bad sign.
Like with most things, the best form of defense against lawn weeds is a good offense. In this case a thriving, healthy lawn. Any bare spots, or where the grass is growing sparsely, allows for weed seeds to settle and sprout.
With the correct watering and mowing schedule, your lawn should form a healthy dense mat that doesn’t allow for invasive grassy weeds to establish. However, if you see a tuft of grass growing taller than the rest of your lawn, or a slightly different color to it, or if you see it starting to form a wheat-like seed head, don’t hesitate to grab it and pull it out before it has the chance to reseed.
About Tom Greene
I’ve always had a keen interest in lawn care as long as I can remember. Friends used to call me the “lawn mower guru” (hence the site name), but I’m anything but. I just enjoy cutting my lawn and spending time outdoors. I also love the well-deserved doughnuts and coffee afterward!
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Common Weeds List
The weeds on this page were originally published on the Whitman County Weed of the Month/Invasive Weeds of Crop and Non-crop Weed Index website. They are republished here by permission of Stephen Van Vleet, WSU Whitman County Extension.
Catchweed bedstraw, Galium aparine L., native to North America and Eurasia, is an annual broadleaf plant with a shallow, branching taproot. The stems of catchweed bedstraw are square in cross-section, weak, mostly unbranched, and grow to about 6 feet long. Catchweed bedstraw prefers shady, moist sites, but tolerates full sun with sufficient moisture. Commonly found in waste sites, roadsides, and other disturbed areas, catchweed bedstraw can grow in a variety of habitats, including along fence lines and in forests and woodlands, meadows, prairies, abandoned fields and cultivated crops.
Downy brome, Bromus tectorum L., was introduced into North America from the Mediterranean area of Europe and is a winter annual that usually begins growing in the fall or early spring. It thrives in all soils. This weed has an extensive shallow root system and roots with many hairs which enable the plant to extract much of the soil water.
Field Bindweed, Convolvulus arvensis L., was introduced from Eurasia. It is a long-lived perennial with an extensive root system, reaching depths of 20 to 30 feet and repeatedly giving rise to numerous long rhizomes (horizontal roots). Field bindweed reproduces by seeds and regenerates new plants from adventitious buds on roots and rhizomes. It is spread by animals, drainage water and machinery, as well as a contaminant of crop seed.
Horsetail, Equisetum arvense L., belongs to a prehistoric plant family that was dominant in the world 230 million years ago and significantly contributed to the formation of coal deposits. The Equisetum family contains over 30 plant species and is native nearly worldwide, excepting Australia, New Zealand, and Antarctica. The Pacific Northwest is home to about 20 Equisetum species.
Horseweed, Conyza Canadensis L. Cronq., is a winter or summer annual, native to North America. The plant grows upright, tall and narrow, and is unbranched at the base unless damaged. A dense inflorescence is borne at the end of branched stems, with small white ray and yellowish disk florets. The leaves and flowers contain a terpene, which may cause skin and mucosal irritation in humans and animals and may inhibit grazing.
Italian ryegrass, Lolium multiflorum Lam., is native to southern Europe, Italian ryegrass is a cool-season, annual or biennial bunchgrass. Mature plants grow 1 to 3 feet tall. Stems (culms) are often purplish at the base, and consist of nodes and internodes. Italian ryegrass regenerates entirely by seed, and germinates readily with sufficient moisture. The plant is best adapted to cool, moist climates, and grows best between 68 and 77°F.
Jointed goatgrass, Aegilops cylindrica, is a winter annual grass native of southern Europe and western Asia. Jointed goatgrass is generally found in areas of 10 to 20 inches of annual rainfall and in elevations of 800 to 4,000 feet.
Kochia, Kochia scoparia L., native to Eurasia, is an annual plant that reproduces from seeds. It has a deep taproot and network of fibrous roots. Mature plants typically range from one to four feet tall, but can grow several feet taller. Because most kochia seeds do not live more than a year, preventing seed production for a single year will significantly reduce the following year’s infestation.
Also known as Dog Fennel, Stinkweed Description Mayweed Chamomile, Anthemis cotula L., is native to the Mediterranean region, but has been widely introduced as a weed in the temperate zones. In 1995, it could be found in almost all of the lower 48 states. Mayweed is an annual bushy, ill-scented herb.
Prickly Lettuce, Lactuca Serriola L., a native to the Mediterranean region is also called wild lettuce, China lettuce or compass plant. The plant is sometimes called the compass plant, because the leaves on the main stem are held vertically in a north-south plane, perpendicular to direct sunlight. Prickly lettuce may be mistaken for dandelion, at the rosette stage, or for sow-thistles at any stage. All of these species are members of the sunflower family, contain milky latex, and produce numerous wind-dispersed seeds.
Rattail fescue (Vulpia myuros) is believed to have originated from Eurasia. Rattail fescue establishes readily and is highly invasive in Mediterranean ecosystems, however, this weed is also widespread throughout temperate and subtropical regions. The greatest populations of rattail fescue exist in the western United States, especially throughout Arizona, California, Idaho, Nevada, Oregon and Washington.
Rush Skeletonweed, Chondrilla juncea L., originated from Eurasia and belongs to the sunflower family. Once established, rush skeletonweed can reduce crop yields by as much as 70 percent. The high fibre content and milky juice in the stems also greatly hamper harvest and tillage operations. Rush skeletonweed infiltrates roadsides, waste areas, disturbed soil, wheat and farm land.
Russian-thistle, Salsola tragus L., Salsola iberica Sennen, introduced from Russia, is a summer annual in the goosefoot family that reproduces by seed. Russian thistle plants break off at the base after maturity and tumble with the wind, scattering seeds over great distances. A single plant can produce 250,000 seeds, which typically remain viable for a year. Russian thistle is commonly found in dryland fields, along roadsides and in disturbed areas. It can reduce yield and quality of crops.
Ventenata (Ventenata dubia (Leers) Durieu) is native to central and southern Europe, Asia, and Africa. Ventenata has established itself in a number of states in the United States and provinces in Canada. It is currently increasing its expansion across the Pacific Northwest and will continue to spread, particularly as a contaminant in grass seed.