Western Integrated Pest Management Center For the latest IPM news and funding announcements, subscribe to our monthly newsletter. Targeting Weed Seeds at Harvest As herbicide-resistant A growing number of experts are making a business out of teaching people how to grow their own pot. Here's what to know to get started.
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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.
As marijuana is legalized in more places, here’s how to grow your own
When it comes to growing his own marijuana, Chris Haynie leaves little to chance.
Inside a grow room in Richmond, Haynie has erected a 42-square-foot tent that houses four marijuana plants, the state’s legal limit for personal cultivation. Haynie’s setup is high-tech: An irrigation system releases moisture on a precise schedule; a motorized LED light timed to mimic the rising and setting of the sun moves along a rail across the top of the tent; and a monitoring system tracks key metrics of plant health, such as the moisture level and pH of the soil, and relays the data to an app on Haynie’s phone. If the system senses urgent problems, he’ll receive a warning text. Haynie’s friends are used to him bolting from a room mid-conversation to tend to his plants.
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Haynie, a bearded 38-year-old cannabis connoisseur who tattooed his thumbs with green ink, is no horticulture amateur. As the co-founder of Richmond’s Happy Trees Agricultural Supply, he’s part of a growing number of experts who are making a business out of teaching people how to grow their own pot. Recent laws in Virginia allow for limited cultivation of marijuana for personal use, and Happy Trees, which Haynie launched in 2019 with Josiah Ickes, 36, specializes in setting up growers to cultivate the plant.
Marijuana remains illegal on a federal level, but many states have abolished restrictions, creating a patchwork of rules throughout the country. Eighteen states and the District of Columbia have passed laws allowing recreational use. Virginia legalized home cultivation in July 2021; under the law, people 21 and older may possess up to an ounce of marijuana. It remains illegal, though, to buy or sell it in any form — including seeds — until 2024, when retail sales are expected to begin.
People still find ways to access seeds. When D.C. legalized the possession of limited amounts of marijuana in 2015, the District lacked the authority to create a legal economic market for sales. So cannabis activists organized seed giveaways throughout the city. At one early event in 2015, lines stretched for blocks.
The regulatory scheme also established what has become an expansive “giveaway market,” in which Washingtonians have used a loophole to provide harvested marijuana as a gift in exchange for the purchase of a legal product. Companies sell cookies, tea or paintings with a baggie of “free” marijuana on the side. One company sells motivational speeches delivered by a person who travels by bicycle.