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Mizzou's weeds team evaluates the Weed Zapper and Seed Terminator

How electricity and impact mills work at weed control.

Kevin Bradley notes one fundamental truth in 17 years as a weed specialist for the University of Missouri: waterhemp woes have only gotten worse.

The “next big thing” in herbicide control of waterhemp has come and gone multiple times, so when Bradley had a chance to look at two new mechanical options of controlling weeds, he jumped at the chance. 

You’ve no doubt heard of the options Bradley and his team have explored:

  • Electrocution, or using high voltage combined with the weed’s water content to fry weeds, thus desiccating and destroying them.  
  • Weed seed destroyers that use a hammermill mounted on a combine to make weed seeds unviable. 

Impressions from The Weed Zapper

The WeedZapper features a trailer-drawn generator that provides up to 15,000 volts of current to a copper boom attached to the front of the tractor. As the tractor moves through the field, the boom electrocutes plants that it touches, desiccating them almost instantly. 

2020 was the first year Mizzou tested the WeedZapper, and researchers determined its likely best fit as a supplement to traditional herbicide-based weed control programs. 

Specifically, the unit is dangerous to operate. Users must remain inside the tractor cab when the WeedZapper is operating, and bystanders need to stay several feet away from the unit. 

“By far, this is more dangerous than anything we’ve ever used before,” Bradley says. 

Mizzou weed scientists used the WeedZapper in soybean plots that had weeds coming through the canopy, with mixed success. The WeedZapper neutralized larger weeds coming through the canopy within a few days. However, it has no residual control of smaller weeds the boom doesn’t touch. Therefore, smaller weeds – those deep in the canopy, below growing soybeans – continue to thrive.

Other observations:   

  • The WeedZapper worked well on weeds with lots of foliage, like ragweed, marestail and waterhemp. It did not work as well on grasses. 
  • A two-pass treatment with the WeedZapper provided better control, at roughly 80% control versus 70% control from a single pass. However, that is probably not necessary if growers are using the machine as a rescue treatment late in the season.
  • Yields in soybeans contacted by the WeedZapper get dinged by 10-15%, depending on soybean growth stage. That’s misleading, as in most cases the WeedZapper electrode will not touch the soybean plants at all. However, when it does, expect to lose some yield, Bradley says. 

The bottom line? The WeedZapper shows potential in its ability to kill weeds, but for row crop users, its best fit is as a weed rescue tool than the first tool growers turn to for weed control. 
“We still recommend residual herbicides with multiple modes of action. But if there are escapes, maybe we can use the Weed Zapper in traditional soybean production systems,” Bradley says. 

Impressions from the Seed Terminator

There is a growing market for mechanical weed destruction tools that attached to the combine and grind up seeds as they leave the chaff spreader. 

Several companies have them available:

All the units work similarly, in that chaff enters an impact mill in the rear of the combine, where rotating bars thrust the chaff against stationary bars. The product emerging from the mills is ground up, chipped or destroyed weed seed. 

Kevin Bradley
Gil Gullickson
2020 represented the second year Mizzou researchers studied the impact of the Seed Terminator on waterhemp seeds. Mounted to a class 8 Case combine, the unit was first used during wheat harvest in 2019. That proved to be a disaster, as the combine got less than 100 feet before it plugged up with green marestail and waterhemp material. 

“Green weeds are an issue,” Bradley says. 

However, it performed flawlessly during soybean harvest, after a frost killed the green weeds. 

In four locations across Missouri in 2019, the Seed Terminator damaged roughly 85% of the waterhemp seeds that came through the combine. “It’s amazing to me that this mechanical instrument can render waterhemp and palmer amaranth – seed the size of a pinhead – unviable,” Bradley says. The efficacy of the Seed Terminator on larger seeds is even greater. “Anything larger than amaranth is rendered into dust. Velvetleaf, lambsquarters, foxtail all are crushed.” 

Other observations: 

  • Combine performance is compromised. Using the combine’s on-board diagnostic system, Bradley and company learned that when the Seed Terminator was operating, the engine load increased about 18% on average, and fuel consumption per hour increased about 4.1 gallons per hour. “But we could hardly tell in the cab that the machine was on,” he says. 
  • Not all weed seeds make it to the chaff spreader. “Thirty-three percent of the seeds never made it through the combine in the first place. That’s something we need to work on,” Bradley says. That leaves two-thirds of the seed making it out the back end. His team also will study weed seeds lost in the grain tank in future years. 

Bradley’s team counted waterhemp plants in select soil cores in Spring, 2020, six months after harvest using the Seed Terminator. In most cases, the number of waterhemp plants in that core was reduced 5-25%, making a small dent in the number of seeds in the soil seedbank.

“Locations already high in number of waterhemp seed in the soil will likely require several consecutive seasons of use before we’ll see reductions,” he says. 

But the Seed Terminator, and other seed destroyer devices, are probably not a silver bullet. 

“This is a tool in an overall program. If this helps us remove seed from the soil, that’s valuable. That’s half the battle,” he says.  

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