PHOTO: UNIVERSITY OF GUELPH PHOTO: PETER ROEK
CROP SCIENCE ▶▶▶
Plant stress makes early season weed control critical
BY MATT MCINTOSH R
esearch from the late 80s established the significant yield impacts weeds can have if not properly controlled early in the growing season, says
Clarence Swanton. He is a weed scientist in the department of plant agriculture at the Univer- sity of Guelph – a notable agricultural research institution in Ontario, Canada. More recently, Mr Swanton and his colleagues investigated what biological mechanisms make this drop – which can amount to several bushels per day in corn and soybeans – possible. According to their findings, such crops are able to detect and communicate the presence of weeds even before seedlings emerge from the soil. That detection cues stress-induced adaptive re- sponses, which have a “rapid and irreversible” negative effect on yield – further reinforcing the importance of early season weed control. “This is actually the science behind why we suggest what we do […] it’s going to have an impact on weed control, on yield potential, cover crop use… all these things you can think about,” he says. “The number one driver of yield potential is the time of weed emergence relative to the crop.”
Plants know what’s coming Mr Swanton says crops can detect the pres- ence of external stressors through several mechanisms, including the release of volatile compounds – used as a warning to others of the species in the event of an insect attack, for example – as well as communication through root systems and changes in light quality. But when it comes to registering weedy threats, light communication is very important. Corn and soybeans can register light reflected from the far-red end of the spectrum by weeds; this initiates stress responses in the crop. Crop seedlings can even perform this detection and responsive action before emerging from the ground, permanently altering its own morphology in ways not conducive to higher
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Do you get anxious when there are weeds in the field? Your crops sure do! New research illustrates how corn and soybeans predict the presence of weeds and respond to it – and how that response has a major yield impact early in the growing season.
yield. And the younger the plant, the more susceptible it is. “Plants don’t compete initially for light water and nutrients. That’s the most significant thing. It changes everything and how we view com- petition,” he says. “You have to be pretty close to the surface to be able to detect above the surface, and at the same time you have to fire the genes and change your morphology,” he continues. “It did all that in the last few centi- metres of the soil. It’s remarkable that it can do that.” Once altered at an early stage, further development can only occur within the now-altered growth parameters. In other words, what has been done cannot be undone.
Too much isn’t healthy The stress processes that actually hurt yield, says Mr Swanton, have to do with the over- production of natural compounds. As corn and soybean plants are stressed, they pro- duce higher levels of hydrogen peroxide (H2
O2) and singlet oxygen (1 O2
), which in nor-
mal amounts have no ill effect. Like alcohol in a person, however, too much can cause dam- age. Energy then needs to be spent to fix that damage, with antioxidants or carotenoids – pigments within the leaves – acting as spong- es to try and absorb excesses and prevent cell damage. Just like people eating antioxidant- rich foods like blueberries,” Mr Swanton says
Weed scientist Clarence Swanton from the department of plant agriculture at the University of Guelph found that crops are able to detect and communicate the presence of weeds even before seedlings emerge from the soil.
▶ FUTURE FARMING | 22 February 2019
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