Toadflax

Linaria vulgaris

Life Cycle

A perennial that spreads by seeds and creeping roots.

Emergence

New shoots and seedlings emerge throughout the season, beginning in midspring. Seeds germinate from very shallow depths and will germinate on the soil surface.

Flowers

This weed flowers from June through fall, with shoots flowering earlier than seedlings.

Reproduction

• Seed
  Toadflax seeds have no dormancy period and can germinate as soon as they are shed. They remain viable for up to three years in the soil.
  
  
• Vegetative
  New shoots emerge from deep, running root stocks. The roots store food for the weed.
  
  

• Tillage
  Summer fallow - Apply the principal of root starvation. Cultivation every three to four weeks, beginning in June, will control but not eliminate toadflax. Where wind erosion is a serious problem, work the land in alternate 80 m (87 yd) wide strips of crop and fallow. Alternate these strips the following year.
  
  Pre-seeding tillage - Tillage before seeding will remove top-growth and give crop seedlings a better chance for establishment.
  
  Post-seeding tillage - This is not effective for control of established stands of toadflax but can destroy existing weed seedlings in cereals. Tillage must be very shallow so that toadflax roots are not spread. However, tillage will encourage a flush of weed seedlings when seeds are brought to the surface.
  
  Fall tillage - Begin tillage as soon as the crop is harvested. Regrowth between tillage operations should not remain above ground for more than five to eight days, until top growth is killed by frost.
  
  
• Rotation
  Alternate fallow and crops to reduce toadflax stands in cereals and prevent interference with grain production. Three cycles of this rotation can reduce toadflax stands by 90 per cent. Fall rye is a good crop to choose for this rotation. Two grain crops can follow a year of intensive cultivation without dramatic increases in the toadflax stand. Post-harvest and pre-seeding tillage are required in this rotation. A perennial grass can follow a year of summer fallow. Bromegrass or crested wheatgrass will compete well against toadflax.
  
  
• Seeding
  Seed cereals at a rate heavier than normal to compete well with toadflax stands.
  
  
• Mowing
  Mowing helps to decrease seed production but will not eliminate toadflax stands.
  
  
• Biological control
  Two insects are already widely established on most toadflax infestations in Alberta, a small beetle, Brachypterolus pulicarius, and a weevil Gymnaetron antirrhini. They feed in the flowers and prevent seed production.
  
  Brachypterolus pulicarius usually appears earlier in the year, damages the tips of the flowering shoots and prevents development of many flowers. Check the flowers on toadflax infestations for these insects. B.
  pulicarius is a small, black, shiny, flat beetle about 2-3 mm in length. G. antirrhini is usually less abundant; it is slightly larger, rounder, duller and dark grey. If these insects are not present, they can be introduced by placing infested toadflax branches among the flowering shoots of toadflax. Take care not to spread toadflax seed around with the insects.
  
  Another insect is being tested in Alberta, the moth Calophasia lunula. The caterpillars of this moth feed on the leaves and flowers of toadflax. They are striking in appearance; the caterpillars are mottled with yellow, black and grey and up to 3 cm in length when full grown. This insect has been established in Ontario since 1962 and is sometimes abundant enough to completely defoliate small patches of toadflax. This insect bred and overwintered in Alberta on the initial release.
  
  For identification of these insects, or to inquire about where to obtain them, contact the Alberta Environmental Centre or Alberta Agriculture, Food and Rural Development.