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Appendix 4: Profiles of Colorado State-Listed Noxious Weeds 255 Yellow toadflax (Linaria vu/garis) Distribufion: Yellow toadflax now occurs throughout the continental United States and in every Canadian province and temtory (Saner et al. 1995). In Colorado, yellow toadflax is abundant on the Western Slope, but can be found on the Front Range as well. It is typically found from 6,000 to 8,500 feet, but can be found up to 10,000 feet. Historical: Yellow toadflax was introduced from Eurasia as an ornamental. BioloevlEcoloev Life cycle: Spring emergence occurs around mid-April and depends primarily on temperature. A smaller flush of seedlings can occur in the fall. Prostrate stems emerge in September and produce leaves that are ovate, 0.9-1.5 inches in size. Prostrate stems are tolerant to freezing and are associated with floral stem production the following yeaz (Robocker 1974). The strong, upright floral stems that are chazacteristic of mature toadflax plants develop after a winter's dormancy, and emerge about the same time as seedlings in mid-April. Flowering occurs from May through August and seeds mature from July through October (Saner et al. 1995). Yellow toadflax is self- incompatible and relies on insects for pollination, The two most important pollinators aze bumblebees and halictid bees (Zimmerman 1996). Mode of reproduction: Yellow toadflax can reproduce both by seeds and vegetatively. Vegetative reproduction enables a stand of toadflax to spread rapidly. Stems develop from adventitious buds on primary and lateral roots. These buds can grow their own root and shoot system, and become independent plants the next year. Yellow toadflax colonies persist mostly via vegetation means while those of Dalmatian toadflax persist both by vegetative and seed reproduction (Lajeunesse 1999). Seed production; A mature plant can produce up to 30,000 seeds annually. A single stem has been reported to contain over 5,000 seeds (Saner et al. 1995). Seed bank: Seeds can remain dormant for up to ten years. Dispersal: Winged seeds aid wind dispersal. Seeds may also be dispersed by water and ants (Rutledge, 1998). Hybridization: No information available. Control Biocontrol: The Division of Plant Industry's Biological Pest Control Section currently has one species, Calophasia lunula, that may be available for redistribution on yellow toadflax infestations. C. lunu/a larvae feed extensively on leaves and flowers of toadflax, severely damaging the plants. Mechanical: Hand pulling toadflax before seed set each year can be an effective control method especially in coazse-textured soils where large portions of the roots can be pulled. However, this method must be repeated as long as [here are viable seeds in the soil (up to 10 years). Cutting or mowing yellow toadflax reduces the current year growth and possibly seed dispersal, but will not kill the plant. These techniques are not recommended to control any toadflax species (Lajeunesse 1999). Fire: Burning is not a recommended control method for yellow toadflax (Saner et al. 1995). The large, deep root system protects the plant from burning. In fact, areas that have been recently disturbed by fire are susceptible to increased toadflax infestation. Herbicides: Effectiveness of herbicides on both toadflax species is highly variable, reflecting in part their high genetic vaziability (Lajeunesse 1999). Yellow toadflax is difficult to control with herbicides. Herbicides should be applied during flowering when cazbohydrate reserves in the root of the plants are at their lowest. Picloram or dicamba at 1 Ib. ai/acre, or glyphosate at 1.5 Ib. aUacre, will kill yellow toadflax plants in some situations. 2,4-D, MCPA, 2,4-DB, MCPB and mecoprop are ineffective on yellow toadflax (Lajeunesse 1999). Picloram+2,4-D at 0.5+1.0 Ib. ai/acre (as Grazon P+D®) controlled 95-100% of yellow toadflax when applied for I-3 consecutive years (Sebastian and Beck 1999). CulturaUPreventive: In agricultural azeas, miminum-till cultivation practices have contributed to the resurgence of toadflax populations (McClay 1992). By not tilling [he soil, and subsequently damaging the root system of toadflax plants, toadflax colonies have been able to flourish. Intensive clean cultivation techniques are recommended for successful toadflax control on agricultural land. This requires at least two yeazs with 8-10 cultivations in the first year and 4-5 cultivations in the second year (Morishita 1991).