Title: Field crops don’t like unwelcome neighbours
[GuelphMercury.com June 14, 2010] It’s a special time of the year. Tiny crop plants such as corn and soybeans are poking through the ground, creeping skyward to capture the sun’s warming rays.And they’re screaming their little green heads off about their no-good, sun-sucking neighbours.At least, that’s what University of Guelph plant scientist Prof. Clarence Swanton hears when he puts his ear to the ground and listens, so to speak, to plants’ response to their environment. A lot of the talk occurs between the plants, and many of the messages are the same: Get lost!
By listening and watching, Swanton, a world-renowned expert in weed control in crops, is making significant discoveries. For example, he’s found field crop plants don’t like crowds, even though they grow closely together in rows. And he’s also found these plants abhor diversity, despite the fact that’s what makes the botanical world go around.
In fact, they know exactly where another plant species has taken root, by the amount of shade the intruder produces and the light it reflects.
If it’s too close, they sound the alarm.
Agronomically, cries for help appear as growth traits. Plants tell Swanton how they feel by dramatically exhibiting characteristics which have a big impact on farming’s ever-important measuring stick — yield.
For example, when crop plants sense nearby competitors (a.k.a. weeds), they muster all their energy and grow longer stems and stalks, to try to out-compete the unwelcome neighbour. This is much like a houseplant’s desperate and often futile efforts in winter to grasp limited sunlight.
But in a very young plant, during what’s called the critical growth period (which lasts about a month), limited energy is available. Something has to give.
Unfortunately, the victim is root development, as the crop plants focus their efforts on stalks and stems. That means farmers end up with spindly, underperforming plants anchored by shallow root systems that struggle to sustain the plants all season.
This is a fairly recent understanding, and it’s fundamentally changed the way farmers approach weed control. Traditionally, they thought they could wait until the weeds emerged, then nail them with what’s called a post-emergent (literally, “after weeds emerge”) herbicide.
But now, by knowing plants’ high stress levels in the presence of weeds, farmers are using more pre-emergent herbicides, to make sure the environment is what Swanton calls “clean” when plants start to grow. Pre-emergent herbicides are applied to the soil, and kill weeds before they get a chance to become competitors. It’s a crucial time to manage weeds, because lost yields can’t be recovered. Delaying spraying by even a few days makes a huge difference in yield.
The down side is that farmers don’t always know what kind of weeds will emerge, or how thick the infestation will be. They don’t want to spray for nothing.
But economically, research by Swanton and others has shown weeds can cut yield on just one corn plant by more than three bushels a day. That’s a lot of money lost. Given that we pay farmers pennies for their crops, they can’t take the chance that their fields will be weedy.
Swanton’s research into early-season weed control has received support from the Ontario Ministry of Agriculture, Food and Rural Affairs, the Natural Sciences and Engineering Research Council and Syngenta. They’re all curious about what his findings mean to science, to farmers and to the crop protection industry.
Hear this world leader in plant research describe the listening phenomenon when he speaks Friday, June 25, at the News@Noon series, from noon – 1 p.m. in the Ontario Veterinary College lifetime learning centre, room 1714. Admission is free, and quite likely so it the advice.