WEEDS

Northern Plains

Wild oats (Avena fatua) is an annual grass and is primarily a weed in spring-seeded small grains. Wild oats flowers and produces seed from June to August. Seeds can be dormant at least 10 years. Dormancy is induced by burying the seed after deep tillage. Wild oats has become a major weed in the canola cropping system, because spring-seeded grains is predominant in the crop rotation and the long seed dormancy. Current control methods are chemical. Labelled compounds include trifluralin, sethoxydim, and quizalofop. Pre-plant incorporated trifluralin gives fair to good control and post-emergence treatment with sethoxydim and quizalofop-P-ethyl gives good to excellent control. In Montana and North Dakota experiments, pre-plant incorporated trifluralin gave excellent control of wild oats. Poast (sethoxydim) applied at third leaf stage of grasses provided excellent control of wild oats. However, the majority of studies have indicated that trifluralin give poor to fair control of wild oats.

Wild buckwheat (Polygonum convolvulus) is an annual plant in the Polygonium family. Wild buckwheat becomes more prevalent when dicotyledons are introduced into the crop rotation; for example wheat - canola, or wheat - lentil, or wheat - flax. Buckwheat in canola can be considered far less competitive than wild oats. Trifluralin, although labelled for controlof some small-seeded broadleaf weeds, gives poor control of wild buckwheat. Pre-plant incorporated trifluralin provided fair to good control of wild buckwheat in Montana; however, this is the exception rather then the rule. With the exception of section 18 labels of clopyralid on canola, no registered herbicide controls wild buckwheat. Clopyralid gives fair to excellent control of wild buckwheat.

Canada thistle (Cirsium arvense) is a perennial weed in the Composite family. Plants are dioecious and the male and female flowers are on separate plants. Flowering occurs in July and August. Plants grow in patches and shoots emerge from deep and extensive horizontal roots. Cutting roots through sporadic tillage without additional chemical control measures increases patch and establishment and size. Canada thistle is a strong competitor, approximately 3 - 4 times more aggressive than wild oats. The herbicides currently labelled in canola do not control Canada thistle. The best control option may be treatment in the fall with glyphosate or clopryalid plus 2-4 D, prior to the season when canola is grown.

Green foxtail (Setaria faberii) is an annual grass. Flowering and seed production occurring in July to September. Data on competitive ability of green foxtail with canola is limited. However, once suppressed early in the season, green foxtail may not compete well with canola due to its smaller size. Currently labelled herbicides give excellent control of green foxtail.

Wild mustard (Brassica kaber) is an annual or winter annual plant of the Mustard family and is closely related to canola. Wild mustard spreads with seed, and can be a contaminant in canola seed. Wild mustard seed can remain dormant in the soil for many years. No chemical is available for control.

Quackgrass (Agropyron repens) is a perennial grass reproducing by seeds or by rhizomes. Broken or cut rhizomes remain viable, therefore mechanical control is difficult. Quackgrass is about as competitive as wild oats. The labelled compounds, quizalofop gives excellent control, sethoxydim gives fair control of quackgrass, whereas trifluralin gives poor control.

Redroot pigweed (Amaranthus retroflexus) is an annual plant from the Amaranthaceae. It reproduces with seed and seeds can germinates any time when moisture is available . No-till systems may favor redroot pigweed occurrence in canola. Fair to good control of redroot pigweed can be achieved with trifluralin. Excellent control may occur with pre-plant incorporated trifluralin.

Russian thistle (Salsola kali) is an annual weed from the Goosefoot family. It reproduces with seed that germinates rapidly, even after small precipitation. Russian thistle is a problem especially in dryer areas and in no-till systems. Trifluralin gives fair to excellent control.

Pacific Northwest

    In addition to weeds mentioned above, in the PNW the following weeds have been identifed as problem weeds,

Common Lambsquarter (Chenopodium album) is an annual weed from the Goosefoot family (Chenopodiaceae). Can be controlled effectively with trifluralin. If not controlled, canola seed yield can be reduced depending on weed density. This weed also can hamper harvest of canola.

Catchweed bedstraw (Galium aparine) is an annual or winter annual weed fromthe Madder family (Rubiaceae). Cannot be controlled with existing registered herbicides. Seeds of catchweed bedstraw are about the same size as canola seed and are difficult to separate. Canola seed quality can be reduced greatly if it is contaminated with catchweed bedstraw.

Southeast

Wild Radish (Raphanus raphanistrum) is the most important weed of canola in the Southeast. Wild radish is cruciferous plant and a close relative of canola. As such, wild radish can not be selectively controlled in canola using herbicides. Radish seed germinate throughout the fall the winter months, however canola can more effectively compete with radish germinating later than 6-8 weeks after planting. Otherwise, radish can be very competitive with canola and can cause 20 to 40% yield loss and well as contaminate seed with radish seed. Infestations are minimized by selecting fields with low levels of wild radish infestations. The weed is controlled in a given field with herbicides in years when canola is not grown. Herbicide resistance technology may have use in controlling weeds in canola in the future.

Italian or annual ryegrass (Lolium sp.) is a winter annual grass weed. Annual ryegrass is a common weed of all winter crops in the Southeast. Trifluralin applied at planting will provide some control of ryegrass. A postemergence application of sethoxydim (Poast) plus crop oil concentrate or quizalofop-P-ethyl provides excellent control of annual ryegrass when applied as a foliar spray. Typically only a portion of fields are infested and require treatment.

Henbit (Lamium amplexicaule) and common chickweed (Stellaria media) are low growing, winter annual weeds. Both weeds germinate in the fall, and infestations can compete with seedling and rosette stage canola. Severe infestations will retard growth of canola seedlings. Trifluralin applied at planting provides good to excellent control of both weeds. Typically, henbit and chickweed only occur in fields that are not treated at planting with trifluralin.

Herbicide Injury

    Potential injury from herbicide carryover from summer crops is an important consideration in Southeast where canola is grown in a doublecrop system. Sixteen herbicides used on cotton, peanuts, corn or soybeans have canola rotational restrictions of 12 to 26 months. These herbicides are nicosulfuron, atrazine, primisulfuron-methyl, cyanazine, flumetsulam, metribuzin + chlorimuron ethyl, chlorimuron ethyl, clomazone, Diuron, fluometuron, metribuzin, linuron, imazethapyr, imazaquin, and norflurazon. Canola is extremely sensitive to herbicides such as chlorimuron ethyl and metribuzin + chlorimuron ethyl. Canola also is sensitive to a number of broadleaf herbicides and can be injured by drift of herbicides applied to other fields (Hudson and Woodruff 1995).

This site was last updated on April 19, 2000 at 04:39 PM -0500