ROW BY ROW / June 2017
Weeds Cause Corn Yield Loss From Day One
Corn yield loss can start even before seedlings emerge from the ground. New research into how plants interact with one another at their earliest stages of development has implications for weed control and preventing yield loss from weed competition as early as the first few hours of a corn plant’s life.
Though the availability of water, light and nutrients is a major primary driver for weed competition early in a corn crop’s development, new research shows processes — namely in the interactions between the crop and other invasive plant species present — at a cellular level can cause plant adaptations early on that can lead to irreversible yield loss. It’s a case, researchers and farmers say, for a “start it clean and keep it clean” approach to weed management in the early stages of a corn crop’s life cycle.
“Once you have that early weed copetition, it can cause you to lose yield and you’re not going to get it back,” says Fenton, Iowa, farmer and Dragotec USA president Dennis Bollig. “You might survive the early-season challenges, but you will restrict that plant’s overall performance, and that leads to yield loss.”
A new approach to weed competition
Clarence Swanton has spent the bulk of the last two decades studying how corn plants communicate with weeds, and what that means to early yield loss potential. That work has yielded a new understanding of the changes corn seedlings undergo that ultimately lead to as much as 3.3 bushels/acre/day of yield loss, says Swanton, a University of Guelph weed scientist in Guelph, Ontario. Plants begin adapting as they are emerging, a fact that led Swanton and fellow researchers on a new path with their research, one that bucks previous theories on when, how and why weeds begin to compete with crops, ultimately robbing them of yield potential.
“The general dogma in weed science is that weeds compete for nutrients, water and sunlight. That’s impossible at these early stages,” Swanton says. “This early, there’s no competition for light, and if you’ve stuck to your agronomic plan, there’s no shortage of fertilizer and there’s typically not a huge shortage of water. So, we started looking at whether plants can detect their neighbors and if there is awareness of other plants around them. The answer is yes.”
Corn plants sense competition
It starts in the leaves of both weed and corn plants. Even before a corn seedling has emerged, it can “sense” the presence of weeds via the phytochrome in those weeds’ leaves. That green pigment in leaf tissue that helps regulate plant growth through photosynthesis gives off a specific “signal,” alerting other plants’ to its presence. And, when a corn seedling receives that signal, it begins adjusting growth patterns to protect it from that weed, and those growth patterns and resulting in permanent, irreversible yield loss.
“We have evidence that even before the corn plant has emerged, it’s already detecting its environment and it’s already making molecular changes based on what it senses above the ground. A plant can suppress photosynthesis, change carbon or root activity or create an explosion of free radicals within the corn plant’s oxygen modules, all because these plants are simply communicating,” Swanton says. “The presence of a weed can trigger a lot of biochemical reactions in the corn plant, and that can lead to oxidative stress.”
It’s that oxidative stress that leads to early yield loss. Plants produce antioxidants to counteract the “free radicals” that are created by oxidative stress. Though antioxidants are effective in knocking down free radicals this stress causes, they take a lot of a plant’s growth resources to produce. The diversion of those resources takes away a lot of energy that would otherwise go toward more normal plant growth. The result is a plant that’s irreversibly altered its growth pattern in a way that promotes yield loss later in the growing season.
“The more antioxidants present, the less damage free radicals can do. If you can’t control oxidative stress — if the antioxidant can’t gobble up the free radicals in a rate that surpasses production of free radicals — that’s when plant damage occurs,” Swanton says. “You can’t see this happening because it’s all going on inside the plant. The plant has to repair oxidative stress damage, and that cost of repair is the loss in yield potential.”
How does this create yield loss?
Though weed competition promotes it from day-one, corn yield loss potential from weed competition often doesn’t show up until later on in the growing season. One key timeframe to watch is the anthesis-silk interval, or the time between pollen shed and silk emergence. While that time window is optimally as small as possible, corn plants influenced by the presence of weeds in the hours and days after planting often have a wider anthesis-silk interval that can influence pollination. And, the wider that interval, the more apt a plant is to see weakened pollination. It’s just one of the vulnerabilities that can show up later in the corn plant’s life and rob it of full yield potential.
“If you cause the anthesis-silk interval to be longer, you have the potential for a rapid rate of yield loss. You don’t get the same kernel set,” Swanton says. “Evidence also suggests if you have delayed weed control, you can make a corn plant more susceptible to the next environmental stress that comes along, like a drought. Changes early on in the seedling’s life cycle, with things like carbon allocation and root structure, influence its ability to withstand stress in the future.”
Keep it clean
Though it’s most likely in the hours and days after planting, yield loss from early weed competition as outlined in Swanton’s research happens in the first month of the plant’s life, up until around the V8 stage, or when it has eight leaves appearing. Because of this early timeframe, it’s important to take a “start clean and stay clean” approach to weed control and herbicide programs. Many farmers who leverage only post-emergence herbicides delay application to maximize the reach of the treatment. Neither strategy alone can eliminate yield loss from weeds altogether.
“Do not delay applying a post-emergence treatment in anticipation of waiting until as many weeds come up as possible. That’s probably the worst possible strategy in the context of our research,” Swanton says. “Start clean and stay clean. Recognize that yield can be lost very quickly and it’s irreversible. If you’re using a post-emerge system, be early. It’s better to be early than to be late with any post system.”
A balanced herbicide program is the best approach to maintaining a clean environment for growing corn plants, Bollig adds. Though pre-emergence treatments can be more effective in keeping weeds from ever even emerging, they lack the consistency of post-emergence products, making them a difficult product on which to base an entire herbicide program. Using both strategies can help eliminate the variability that inconsistent early weed control can have later on when the combine runs.
“Pre-emergence herbicides are not a given because of weather variables. Post-emergence herbicides are going to create some variability if you use them alone, too. It’s best to take a balanced approach to get the best protection for your crop,” Bollig says. “But every herbicide program has the potential to create yield variability and you’ll have to deal with it at harvest.”
Accounting for variability at harvest
Though Swanton’s research gives hope that weed pressures may one day be a thing of the past, the variability in corn yield because of the presence of invasive species is unavoidable. Even the slightest weed presence can lead to inconsistent yields. That makes it important to operate machinery that accounts for that variability in yield, from planting to harvest.
“There’s no question that Mother Nature creates variables in our plan to create crop uniformity. The question has always been ‘How fast can you or your equipment react to those variables to reduce potential yield loss?’” Bollig says. “It isn’t whether you’ll have that variability, but how quickly you can react to it. Drago corn heads are unmatched in harvesting variable fields. No field is perfect, but when we approach the crop knowing that’s reality and using the right equipment, we can work toward that goal of perfect uniformity.”