Toadflax, Yellow

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Pest Information
Common Name: Toadflax, Yellow
Family Name: Scrophulariaceae
Latin Name: Linaria vulgaris Mill.
Other Names: Butter and eggs, wild snapdragon, common toadflax, ramsted, flaxweed, Jacob's ladder
Provincial Designation: Noxious
Life Cycle: Perennial
Mode of Spread: Seed, Vegetative

Detailed Information
Description: Toadflax is a perennial weed that spreads through an extensive creeping root system that forms dense patches. The stems are smooth, green, up to 8.0 cm tall and sometimes branched near the top. The numerous narrow, hairless leaves are 2.4 – 5.5 cm long and 0.6 – 1 mm wide and pointed at both ends. There is one leaf per node (alternate leaf position), but the leaves appear opposite due to crowding. The flowers are bright yellow with an orange spot on the lower lip (like snapdragon flowers, to which they are related), 2 – 3 cm long on short stalks and densely spaced. The backward pointing spur is about half the length of the flower. The seeds are dark brown, about 1.4 – 2.1 mm in diameter and 0.5 mm thick with dark brown or black papery circular wings that enable them to be disseminated readily by the wind over long distances (Saner et al. 1995).
Growth and Development (Life Cycle): Emergence: New shoots and seedlings emerge in mid-spring when soil temperatures rise to 4 – 5 degree C, and they may continue to emerge throughout the growing season.
Seed Production: Yellow toadflax is a prolific seed producer; a single plant has the potential to produce up to 30,000 seeds.
Seed germination: Yellow toadflax requires open soil for germination. Germination usually occurs in the top 2 cm of soil
Dormancy: Seeds may germinate immediately or may remain dormant up to 8 years.
Dispersal: Seeds are winged and can be carried by the wind. Water and ants may also disperse yellow toadflax.
Where it Grows (Habitat & Ecology): It occurs in wide variety of habitats such as roadsides, waste areas, rangeland, hay fields, forage crops, conventionally tilled and reduced tilled fields.
Reproduction (Dispersal): Seed: Yellow toadflax is a prolific seed producer; a single plant has the potential to produce up to 30,000 seeds. Although wind, water, birds may disperse the winged seeds, rodents and ants, the majority fall within 0.5 m of the parent stem. Freshly collected seeds have low (40 – 50%) germination. Vegetative: The vegetative reproductive capability of toadflax is remarkable, ensuring its spread and persistence.
Vegetative:Vegetative reproduction from root buds starts as soon as 2 – 3 weeks after germination, and the creeping root system can expand 1– 2 m per year. Lateral root fragments as short as 1 cm can be viable. This vegetative reproduction results in dense patches of toadflax that may often have several hundred stems m-2. Lateral roots can withstand freezing to -15°C, a temperature rarely experienced at root depth in Alberta. Roots can penetrate more than 1meter deep, thus providing drought tolerance.
Economic Importance (Beneficial Aspects): Detrimental: Yellow toadflax is a persistent, aggressive invader, capable of forming dense colonies; it can suppress native grasses and other perennials, mainly by intense competition for limited soil water. This species contains a poisonous glucoside that is reported to be unpalatable and moderately poisonous to livestock. Toadflax is an alternate host for tobacco mosaic virus.
Origin: Southeastern Europe and southwestern Asia
Flowering: Flowering timing: July to September
Flower Color: Yellow with dull orange center
Yield Losses: Yellow toadflax is very competitive and reduces the yield of many field crops. In canola and wheat, infestations of 12 and 74 yellow toadflax stem m– 2 respectively, reduced yields by 20% (O’Donovan and McClay 1987; O’Donovan and Newman 1989).
How to Control: Integrated Weed Management
Tillage: intensive tillage has been used to control yellow toadflax. It can, however, cause soil erosion and is not compatible with current soil conservation practices. Moreover, if tillage is not done correctly, physical disturbance can readily spread yellow toadflax as small root fragments can produce new shoots.
Higher Seeding Rate: Research carried out at Lacombe Research Station has shown that a high seeding rate reduces toadflax densities and provides suppression of toadflax in the absence of preharvest glyphosate (Harker et al 1995).
Crop Rotation: Alternate fallow and crops to reduced toadlax stands in cereals and prevent interference with grain production. Three cycles of this rotation can reduce toadflax stands by 90 percent. However, tillage intensive fallow is not compatible with current soil conservation practices.
Higher Fertilizer Rate: Well-fertilized grass forage stands can provide strong competition and suppress toadflax.
Chemical Control: Herbicides that are effective in the management of yellow toadflax are limited. Metsulfuron methyl (Ally), thifensulfuuron plus tribenuron (Refine Extra), and a tank mixture of 2,4-D and dichlorprop (Estaprop) suppress yellow toadflax seedlings in cereal crops. No herbicide is registered for the control of yellow toadflax. Recently however, an integrated weed management technique was developed for the effective control of yellow toadflax (Baig et al. 1994). This method combines tillage and fall applications of glyphosate during a summer fallow year. Infested fields are cultivated 2 to 3 times from mid May to mid July. After the last tillage operation, yellow toadflax is allowed to regrow for a minimum of 4 weeks; glyphosate is then applied to actively growing yellow toadflax plants. This technique, although very effective, has a limited fit in direct seeding systems as summer fallow is becoming less common and less desirable.
Yellow Toadflax Control in a System Approach
Controlling Small Patches
The first step in a yellow toadflax control program is to determine the extent of the infestation. If the toadflax occurs in small, distinct patches, spot treatment may be adequate. Mark the patches and apply a herbicide, such as glyphosate (various products), amitrol (Amitrol 240) or picloram (Tordon 22 K). In subsequent years, monitor these patches for re-infestation and re-spray if necessary. Spot treatment of small toadflax patches in cropland is better suited to glyphosate because of its non-residual character, than amitrol or picloram. However, these patches will likely need re-treatment over the next few years to achieve complete kill and deplete the seed bank.
Field Scale Infestation:Once toadflax becomes well established in a field, herbicide strategies become limited and costly. In-crop cereal herbicides such as Ally, Refine Extra and Estaprop can only suppress mature toadflax plants, but they are useful in controlling young seedlings.
Pre-harvest application of glyphosate: Preharvest application of glyphosate in wheat, barley, oats, canola, flax peas and lentils is quite effective on yellow toadflax with 90 – 95% control 1 year after application (Baig et al 1995), and it should be a key part of the control strategy
Prior to seeding:Pre-seeding glyphosate also provides some suppression (unregistered treatment), and it should be combined with in-crop sprays or pre-harvest treatments.

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Last Modified: December 20, 2011

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