CARMAN, Man. – Correctly identifying weeds starts when plants are young.
It may seem like a simple task, but making an error at this point can result in wrong herbicide selection and little or no control of the weed, said Kim Brown-Livingston, chief instructor at the 23rd annual Weed Seedling ID Day held May 23 at the University of Manitoba research farm in Carman.
“You have to pay careful attention to detail.”
Manitoba Agriculture traditionally schedules the school on the third Wednesday in May to coincide with the emergence of weeds and the usual identification challenges encountered at this time of year.
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The school is free and registrants included certified crop advisers, weed supervisors, industry agronomists, agriculture students, producers and others wanting to hone their weed identification skills.
This year the school featured 60 common prairie weeds at their typical growth stage for this time of year.
Brown-Livingston said grass seedlings are the most difficult to identify because at this stage all species look alike.
“You need to concentrate your attention on what makes each grass seedling species different, not what makes them look the same,” she said.
“Pull apart the cotyledons. That’s the first pair of leaves originating from the seeds – the seed leaves. If you focus on the auricle, you can see that different grasses are visually distinct right at this point because the ligule inside the auricle is different.”
She said the auricle is the earlike appendage that wraps around the stem of some grass species at the junction of the leaf blade and the stem.
The ligule is the short flap of membrane tissue or fringe hairs on the inside of a grass leaf where the blade joins the stem. It often looks like a collar that sticks straight up from inside the stem.
According to BASF’s grassy weed guide, the ligule is the outgrowth on the inner side of a grass leaf at the point where the sheath joins the blade.
Brown-Livingston said not all grass species have visual traits such as an auricle or ligule, which can also be a clue when identifying the weed.
“If it doesn’t have the ligule, it automatically disqualifies itself from certain grass groups. For example, if it doesn’t have a ligule, we know right away it cannot be wild oats or green foxtail. The lack of visual traits sometimes tells us as much as when we see the traits,” she said.
“Our three grass seedling categories are membranous ligules, hair-like ligules and grasses that have no ligules at all.”
She said wild oats are a good example of a grassy weed with a membranous ligule. Wild oats have a counterclockwise twist to the leaf and no auricle and the ligule is a membrane rather than hair or fringes.
Green foxtail is a common hair-like ligule species with a ligule that looks like a fringe of hair about two millimetres long. There is no auricle and the young leaves have fine, upward pointing barbs.
Barnyard grass has no auricle or ligule and the seed leaves have fewer than three solitary hairs at the base of the blade.
Weed specialists warn against using colour to identify weeds. Ingrid Kristjanson, a farm production adviser with Manitoba Agriculture, said purpling or reddening can be associated with some weeds, such as red root pigweed, but it can lead to a wrong identification.
“You have to be aware that purpling and reddening can also be a result of environmental conditions. A cold snap can induce colour change in many different weeds,” she said.
“If you use purpling or reddening as a determining factor, you can make the wrong identification. For example, barnyard grass has reddening, but you can also get the same kind of reddening in foxtail.
“Colour helps, but it should not be the determining factor in weed ID. If you make the wrong ID and spray with the wrong product, you’ve wasted your money and the weed continues to grow.”
Kristjanson said staging is also an important factor, which is reflected in the tendency of weed guides to refer to the two-leaf to four-leaf stage or the two-leaf to six-leaf stage.
Once the weed is beyond that target stage, the degree of herbicide success is usually reduced, which is a major reason for staying on top of weed identification early in the growing season.
Kristjanson also stressed the need for clean water when spraying glyphosate. She said dirt in the water binds up the glyphosate and the farmer might as well be spraying glyphosate on bare soil.
“The same thing happens with dust on the leaves,” she said.
“Dust on the leaves is dirt on the leaves. It binds up the glyphosate as soon as it touches the leaves.”
For more information, contact Manitoba Agriculture weed specialist Bruce Murray at 204-745-5651.
