Field pennycress
Thlaspi arvense L.



Images above: Upper left: Field pennycress seedling (Antonio DiTommaso, Cornell University). Upper right: Field pennycress fruit (Scott Morris, Cornell University). Bottom: Field pennycress plant (Scott Morris, Cornell University).
Identification
Other common names: bastardcress, fanweed, stinkweed, penny cress, mithridate-mustard, frenchweed, French-weed, bastardweed, dish mustard, field thlaspi
Family: mustard family, Brassicaceae
Habit: Erect, branched, summer or winter annual herb.
Description: Cotyledons are hairless, unequally sized, 0.2-0.4” (0.5-1 cm) long by 0.1-0.3” (0.25-0.75 cm) wide, oval shaped, and bluish-green in color. The first leaves on the seedling are opposite and oval shaped, with wavy margins; all subsequent leaves are alternate. Young leaves form a basal rosette. Mature plants reach 20-30” (51-76 cm) tall. Basal leaves are long stalked 0.5-2” (1.3-5 cm); the blades are pale green, hairless, 1-2.5” (2.5-6.4 cm) long, obovate, and they wither at maturity. Stem leaves are stalkless, dark green, irregularly toothed, lance to linear, 0.75-2” (1.9-5 cm) long, and tapered; they persist to maturity. Pointed auricles are present at the base of stem leaves. An extensive fibrous root system extends from a thin taproot. All plant parts exude an unpleasant odor when crushed. Flowers are inconspicuous, 0.13” (0.3 cm) wide, have four white petals and are clustered at stalk ends. The stalk continues to elongate at maturity, producing new flowers at its tip and maturing seeds below. Seedpods are round, 0.5” (1.3 cm) wide, and flat with winged, papery edges. Seedpods have a central line and a notched tip; the notch is deeper than it is wide. Seeds are light to dark brown or purplish, 0.06” (0.15 cm) long, and ovate. Seeds have one straight side, one round side, and distinctive fingerprint-like surface ridges.
Similar species: Shepherd’s-purse [Capsella bursa-pastoris (L.) Medik.] seed pods are more heart or triangular shaped and the flower stalks are mostly leafless and unbranched. Thoroughwort pennycress [Microthlaspi perfoliatum (L.) F.K. Mey.] has smaller seeds contained in 0.25” long, wider notched seed pods and has rounded auricles.
Management
Delaying planting of both spring and fall seeded crops allows more field pennycress seeds to germinate before tillage. Where feasible, rotation with summer planted crops reduces field pennycress populations, but only if the weed is prevented from setting seed in the spring before planting. Early spring cultivation during the fallow year of grain-fallow rotations will prevent seed production and improve good control. Otherwise, field pennycress produces seeds exceptionally early in the spring and substantial seed input can occur in fallow fields while other fields are being prepared and planted with crops. Some winter wheat varieties are substantially more competitive against this weed than others (Holm et al. 1997) and the same probably applies for other grains. Since the species does not tolerate shade, tall leafy small grain varieties are likely to be more competitive. Banding N in grain crops decreases the density of field pennycress (O’Donovan et al. 1997). A substantial fraction of field pennycress seedlings can be selectively removed from many crops with well timed tine weeding but usually many will survive. Unlike most annual weeds, field pennycress populations are not reduced by rotation into alfalfa (Warwick et al. 2002). Fall germination and early spring seed production allows field pennycress to complete its life-cycle while avoiding competition with alfalfa. Also, mowing causes branching and rapid regrowth, with little reduction in final plant size or seed production. Smooth brome and crested wheatgrass, however, effectively suppress field pennycress.
In vegetable crops, use dense winter cover crops of rye or spelt to suppress field pennycress, but be sure to incorporate these in the spring before the weed goes to seed. Rework the seedbed before planting to flush seeds out of the soil and kill seedlings. Tine weed or hoe around crops until they are well established to eliminate early flushes.
Ecology
Origin and distribution: Field pennycress originated in Eurasia and is widespread from Japan to Spain. It is present throughout the U.S.A. and in Canada as far north as the Yukon, but it is most problematic in the northern Great Plains region (Warwick et al. 2002). It has also been introduced into Australia, New Zealand and Argentina. (Holm et al. 1997, USDA 1970)
Seed weight: 0.74-1.44 mg (Gescha et al. 2016), 0.79 mg (Stevens 1932), 0.99-1.12 mg (Werle et al. 2014), 1.1-1.5 mg (Matthies 1990).
Dormancy and germination: Various strains of the species show differing germination behavior. In most field-grown populations, seeds are dormant when shed from the parent plant and require an additional month or more of after-ripening (Baskin and Baskin 1989, Hazebroek and Metzger 1990, Hill et al. 2014, Warwick et al. 2002). Seeds of various strains respond differently to cold. For some non-dormant strains, cold temperatures, for example 36 °F (2 °C), induce deep dormancy (Baskin and Baskin 1989) that is only broken by exposure of the seeds to several months of warmer 43-95 °F (6-35 °C) temperatures (Hazebroek and Metzger 1990). In other dormant strains, several weeks of cold temperatures breaks dormancy (Baskin and Baskin 1989). Regardless of strain, during the transition between dormancy and non-dormancy, germination is promoted by red light, but inhibited by light filtered through a crop canopy (Baskin and Baskin 1989, Hazebroek and Metzger 1990). Light is particularly effective when it occurs during a cool to warm temperature transition (Saini et al. 1987). Nitrate also induces germination of seeds exposed to light (Saini et al. 1987, Warwick et al. 2002). Day/night temperature fluctuations promote germination (McIntyre and Best 1975), except for dormant seeds (Hazebroek and Metzger 1990). All of these factors probably contribute to the flush of germination that commonly follows fertilization and tillage (Warwick et al. 2002). Non-dormant seeds are capable of optimum germination at a wide range of day/night temperatures from 59/43 °F (15/6 °C) to 95/68 °F (35/20 °C) (Baskin and Baskin 1989). Germination of this species requires relatively higher soil moisture compared to crops (Hazebroek and Metzger 1990).
Seed longevity: The seeds can persist 17 to 30 years in undisturbed soil (Burnside 1996, Mitich 1996, Toole and Brown 1946). In a five-year experiment, the number of field pennycress seeds declined by 50% per year in soil stirred four times per year, but only 10% per year in undisturbed soil (calculated from Roberts and Feast 1972).
Season of emergence: Most emergence occurs in the spring, relatively few individuals emerge in mid-summer, and a second, usually smaller, peak of emergence occurs in the fall (Chepil 1946, Werle et al. 2014). In Wisconsin, field pennycress is among the earliest weeds to emerge in spring (Doll 2002). However, when seeds are shed on the soil surface in spring, the majority emerged in the fall and few are left to emerge in the following spring (Baskin and Baskin 1989).
Emergence depth: Most seedlings of field pennycress emerge from the top 0.8” (2 cm) of soil (NAPPO 2003). The emergence requirements of a shallow seed depth combined with high soil moisture may explain why non-dormant seeds capable of germinating at high temperatures do not emerge in mid-summer when surface soil is usually dry (Hazebroek and Metzger 1990).
Photosynthetic pathway: C3
Sensitivity to frost: The species is very cold hardy (Stevens 1924), and cold acclimated plants can survive 7° F (-14° C) with little damage (Cici and Van Acker 2011). Field pennycress cold tolerance increased from 23 °F (-5 °C) to 1 °F (-17 °C) over a three-week cold acclimation period (Sharma et al. 2007). Fall germinating individuals over-winter and flower the following spring. Plants that begin flowering in the fall sometimes over-winter and continue seed production in the spring (Warwick et al. 2002).
Drought tolerance: The root system of field pennycress has a higher density and total length than most grain crops and other weeds, which makes the species a good competitor for moisture (Holm et al. 1997). Relative to other species, however, field pennycress requires more water per unit of growth.
Mycorrhiza: This species is non-mycorrhizal (Harley and Harley 1987, Warwick et al. 2002).
Response to fertility: Plant size increases steadily with increasing nitrogen application rate up to 143 lb N/A (160 kg N/ha), and field pennycress was categorized as intermediate in N response relative to other weed species (Blackshaw et al. 2003). The species also continues to respond to phosphorus fertilization up to very high application rates (Blackshaw et al. 2004). Fruit and seed numbers per plant increased with a balanced N-P-K fertilizer treatment (Benner 1988).
Soil physical requirements: Field pennycress occurs on all types of soil suitable for crop production (Warwick et al. 2002).
Response to shade: The species is intolerant of shade, and usually cannot push through a crop canopy (Holm et al. 1997).
Sensitivity to disturbance: Removal of the shoot tip increases branching but has little effect on mature plant weight or seed production (Benner 1988). Seeds in green pods will continue to mature even after being plowed under (Holm et al. 1997).
Time from emergence to reproduction: The species exists as early-flowering and late-flowering strains, but exposure of either seeds or over-wintering rosettes to cold largely overcomes the genetic control of flowering time (McIntyre and Best 1975, Warwick et al. 2002). Generally, as temperatures increase, early-flowering plants take less time to flower, whereas late-flowering plants take longer to flower (McIntyre and Best 1975). Plants of either strain that establish in the spring flower 5-7 weeks after emergence (Doll 2002, Warwick et al. 2002), but over-wintering plants flower a month earlier (Warwick et al. 2002). Early spring flowering lines complete their life cycle rapidly enough in spring to potentially be domesticated as a rotational crop in a corn-soybean rotation (Dorn et al. 2017). The seeds require about 2 weeks to fully mature; however immature seeds become viable as little as 6 days after pollination (Hume 1984).
Pollination: Self-pollination is common, but 10-20% of flowers are cross pollinated by insects (Warwick et al. 2002).
Reproduction: Field pennycress may produce from 1,600 to 15,000 seeds per plant (Mitich 1996, Stevens 1932). Spring emerging plants in Saskatchewan with little competition produced an average of 14,000 seeds/plant, whereas fall emerging plants produced an average of 9,400 seeds/plant (Warwick et al. 2002). Field pennycress averaged 300 seeds/plant in high density monocultures (Hill et al. 2014).
Dispersal: Seeds are dispersed in soil on tires, field machinery, and shoes, and by combines. It is commonly found in manure and can survive digestion in the guts of transported livestock (Blackshaw and Rode 1991). Viable seeds have been recovered from droppings of several species of wild birds. It is also a common contaminant of grain and forage seed, which is a major way it has moved between continents. The seeds disperse short distances with wind, and longer distances in irrigation water. (Holm et al 1997, Mitich 1996, Warwick et al. 2002)
Common natural enemies: Field pennycress is susceptible to the pathogens and insects that commonly attack crops in the mustard family, but there is no record that damage levels are detrimental to growth or reproduction. Carabid beetle activity was highly correlated with field pennycress seed predation from the soil surface; losses from fields in late summer averaged 23% per week (Kulkarni 2016).
Palatability: Consumption by cattle gives meat and milk an unpleasant flavor, and in large quantities can cause poisoning. Field pennycress seeds can contaminate canola and lower the quality of canola oil. The species is cultivated in parts of Europe for the tender young shoots, which are eaten in salads or cooked like spinach. (Mitich 1996, Warwick et al. 2002)
Note: Field pennycress is currently being developed as a winter annual oilseed crop that would be complementary with a corn-soybean rotation in the upper Midwest. It also has potential as a winter hardy cover crop that can provide early spring pollinator services. (Dorn et al. 2017, Eberle et al. 2015)
References
- ARS. 1970. Selected Weeds of the United States. U.S.D.A., Agricultural Research Service, Agricultural Handbook No. 366: Washington, DC.
- Baskin, J. M., and C. C. Baskin. 1989. Role of temperature in regulating timing of germination in soil seed reserves of Thlaspi arvense L. Weed Research 29:317-326.
- Benner, B. L. 1988. Effects of apex removal and nutrient supplementation on branching and seed production in Thlaspi arvense (Brassicaceae). American Journal of Botany 75:645-651.
- Blackshaw, R. E., R. N. Brandt, H. H. Janzen, T. Entz, C. A. Grant, and D. A. Derksen. 2003. Differential response of weed species to added nitrogen. Weed Science 51:532-539.
- Blackshaw, R. E., R. N. Brandt, H. H. Janzen, and T. Entz. 2004. Weed species response to phosphorus fertilization. Weed Science 52:406-412.
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- Eberle, C. A., et al. (10 additional authors). 2015. Using pennycress, camelina, and canola cash cover crops to provision pollinators. Industrial Crops and Products 75:20–25.
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- Sharma, N., D. Cram, T. Huebert, N. Zhou, and I. A. P. Parkin. 2007. Exploiting the wild crucifer Thlaspi arvense to identify conserved and novel genes expressed during a plant's response to cold stress. Plant Molecular Biology 63:171-184.
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