Iris pseudacorus L.
Yellow Flag IrisCategory |
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Forb/Herb |
Description
Iris pseudacorus is a herbaceous perennial that can grow up to 0.9-1.2 m (3-4 ft.) in height and the only completely yellow iris in North America.Stem
5-10 dm highLeaves
Leaves are very long, linear, pale-green, glaucous, stiff, 8-16 mm wide. Sword like flattened leaves about ¾ of an inch wide and up to 3 feet long.Flowers
The showy flowers of Iris pseudacorus bloom from April to June. Bright yellow flowers bloom in groups of 2 to 10 atop a 1-3 ft. stem. Most often the flowers are yellow, but their color can also range from nearly white to cream. The flowers are 7-9 cm (2.75-3.5 in.) wide. They are borne on erect peduncles and there are several flowers on each stem. There are six perianth segments that are clawed. Three of these are upward-pointing petals and three are downward spreading sepals. These sepals often have purple, brown or red veins on their yellow surface.Fruit
Fruits are 1.6-2.7 in. (4-8 cm) long capsules. The capsules are 6-angled and cylindric-prismatic to ellipsoid. The average capsule contains about 120 white seeds that harden and turn brown as they matureImages
Photo: Nancy Loewenstein, Auburn University, Bugwood.orgMore images of Iris pseudacorus
Life History
Habitat
Iris pseudacorus can be found along the edges of lakes, ponds, rivers and streams and immersed in water up to 25 cm (10 in.) deep. It grows well in freshwater wetlands and can tolerate high acidity. In its native habitat, Iris pseudacorus can tolerate living in the upper zones of salt marshes, where it may be surrounded by saline water. The plant also tends not to favor calcareous substrates, though there are exceptions to this, such as along the Housatonic River of Connecticut. It may also be found in floodplain forests and may be an ornamental in gardens.Origin and Distribution
Europe, Caucasus Mountains, Western Asia, North Africa.h2. Management Recommendations
Mechanical Controls
Manual or mechanical methods that remove the entire I. pseudacorus rhizome mass can successfully control small, isolated patches. These methods, however, are very time and labor-intensive, since even small rhizome fragments can resprout. Additionally, digging disturbs the soil, may fragment rhizomes, and promote germination of I. pseudacorus and other undesirable species from the soil seed bank (Jacono 2001).Pulling or cutting I. pseudacorus plants may provide adequate control, but only if it is repeated every year for several years to weaken and eventually kill the plant. Dead-heading (removing the flowers and/or fruits) from plants every year can prevent seed development and seed dispersal, but will not kill those plants (Crawford 2000). Care should be taken when pulling, cutting, or digging I. pseudacorus since resinous substances in the leaves and rhizomes can cause skin irritation (Cooper & Johnson 1984 in Jacono 2001).
Cutting the foliage, followed by a herbicide application (see below for details), can provide good control with minimal off-target effects (Jacono 2001).
Herbicidal Controls
Iris pseudacorus can be effectively controlled by herbicides. Since it usually grows in or adjacent to water, an aquatic-labeled herbicide and adjuvant must be used. Glyphosate (for example, tradenames Rodeo®, Aquamaster® or Glypro®) applied in a 25% solution (13% a.i.) using a dripless wick/wiper applicator, or applied in a 5 to 8% solution if sprayed, when used with the appropriate non-ionic surfactant adjuvant, can effectively kill I. pseudacorus.The timing and choice of application technique will determine control efficacy and should work to minimize off-target effects. Iris pseudacorus can be controlled by either directly applying the herbicide to foliage, or by immediately applying herbicide to freshly cut leaf and stem surfaces. Herbicides can be directly applied to I. pseudacorus foliage or cut stems by a dripless wick system or using a backpack sprayer. Be sure to always take appropriate precautions and wear suitable clothing and equipment, and follow all instructions on the herbicide label. Use a dye in the herbicide mix so you can watch for accidental contact or spill of the herbicide.
Biological Controls
There are currently no biological control agents available for I. pseudacorus control, although it is fed upon by several invertebrates and fungi. Invertebrates known to feed upon it include: the beetles Mononychus punctumalbum and Aphthona nonstriata, the flies Atrichopogon pollinivorus, Cerodontha ireos, C. iridis, and Eumerus strigatus, the true bugs Pachybrachium fracticollis, Cymus glandicolor, and Adelphocorus ticinensis, the aphid Aphis newtoni, and Lepidoptera Amphipoea crinanensis, Archanara algae, A. sparganii, Xylena vetusta, Celaena leucostigma, Diacrisia metelkana, Dydraecia micaceae, Orthotailia sparganella, Plusia festucae, Sparganothis pilleriana, Spilosoma urticae, and Clepsis spectrana. Additionally, the following fungi are known to feed upon Iris: Ascochyta pseydacori, Belonium nigromaculatum, Belonopsis iridis, Botryotinia convulata, Ectostroma iridis, Mycosphaerella iridis, M. macrospora, Nectriella dacrymycella, and Phoma pseudacori. The plant disease Pseudomonas iridis (iris root rot) has also been found on I. pseudacorus and can cause premature yellowing of the leaves and rot the rhizomes. However, none of the above mentioned pests or pathogens has been investigated for their potential as biocontrol agents against I. pseudacorus.Bibliography
EDDMapSJacono, C.C. 2001. US Geological Survey Invasive Fact Sheet: "Iris pseudacorus":http://nas.er.usgs.gov/plants/docs/irpseud.html. Accessed January 16, 2003.
Piccardi, E.B. and M. Clauser. 1983. Absorption of copper by Iris pseudacorus. Water, Air, and Soil Pollution 19(2): 185-192