Purple loosestrife [Lythrum
salicaria L.][LYTSA][CalEPPC: Red Alert][CDFA list: B] Photographs
Map of Distribution Biocontrol
[Lythrum hyssopifolium L.][LYTHY] Photographs
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Stems simple or branched, sometimes +/- square or 5-angled. Leaves
sessile, margins smooth. Stipules lacking.
and UNDERGROUND STRUCTURES:
FLOWERS: Calyx tube
(hypanthium) cylindrical, 4-6 mm long, longitudinally
8-12-ribbed, with 4-6 triangular sepal lobes 0.5-1 mm long
at the top and longer appendages in between.
Petals 4-6(7). Ovary superior but appears inferior, surrounded
by and not fused to calyx tube. Insect-pollinated.
and SEEDS: Capsules oblong-ovoid, surrounded by persistent
calyx tube, open into halves at tip. Seeds numerous, flattened,
sometimes 3-angled in cross-section, often concave on 1 side,
0.5-1 mm long.
CHARACTERISTICS: Above ground parts
of purple loosestrife typically die in late fall. Senescing
foliage often turns red. Dead brown stems often persist through
winter, are oppositely branched, and may retain a few capsules.
primarily by seed. Stem fragments can develop roots under
favorable conditions. Seeds disperse with water, mud, human activities,
and by clinging to feathers, fur, and feet of animals.
FAVORING/DISCOURAGING SURVIVAL:purple loosestrife:
Monitoring uninfested areas and hand-pulling newly discovered
seedlings before seed is produced can help prevent the spread
of purple loosestrife. Cutting flowering stems followed
by flooding can help control but not eliminate dense infestations.
Cut stems can re-root under certain conditions. Plants are most
susceptible to systemic herbicide effects during the late flowering
Spatulaleaf loosestrife [Lythrum portula (L.) D.
Webb, synonym Peplis portula L.][Bayer code: none] and
threebract loosestrife [Lythrum tribracteatum Salzm.
ex Spreng.][Bayer code: none] are wetland plants introduced from
Europe that resemble hyssop loosestrife. Spatulaleaf
loosestrife is a creeping summer annual that roots
at the nodes and has inconspicuous white to pink flowers ~
2-3 mm long. Unlike hyssop loosestrife, spatulaleaf
loosestrife has bell-shaped calyx tubes 1-2 mm long
and fleshy spoon-shaped leaves that gradually tapered
to a narrow base. Northern Sierra Nevada, to 2200 m (7200
ft). Threebract loosestrife is a summer annual to
short-lived perennial with +/- obovate leaves. Unlike
hyssop loosestrife, threebract loosestrife
has triangular calyx tube appendages that resemble the
sepal lobes and are covered with red glands. Central Valley,
San Francisco Bay region, and northern Modoc Plateau, to 1500
m (4900 ft). California loosestrife [Lythrum californicum
Torrey & A. Gray] is a native perennial that
may be mistaken for purple loosestrife. However, under
most circumstances California loosestrife is not considered
a weed. Unlike purple loosestrife, California
loosestrife has glabrous stems, petals mostly 4-8 mm long,
and linear inflorescence bracts with acute or rounded
tips. California loosestrife occurs on wetland sites
in the southeastern North Coast Ranges, Sierra Nevada foothills
and high regions of the southern Sierra Nevada, Central Valley,
Central- and Southwestern regions, and Desert regions, to 2200
m (7200 ft).
Mechanical: includes mowing or cutting, pulling, and digging.
While mowing is generally ineffective, mowing timed at the bud stage may reduce
seed production. Cutting earlier may increase stem densities and mowing after
seed production only serves to spread the infestation. Mowing is frequently
not an option in most wetland areas, drainages, or along water courses. Hand
pulling or digging results in more disturbance, but may be successful on small
infestations. Young plants are most easily pulled, while older plants may require
digging. New plants may emerge from missed roots or from stems left lying in
contact with moist soil.
Biological: Biocontrol is probably the most viable option
for long-term control of large purple loosestrife infestations. At least four
insects are currently being tested in California, but none are currently available
for release. Two species of leaf-eating beetles (Galerucella calmariensis and
G. pusilla) have had considerable success in reducing purple loosestrife in
other states and may be promising here in California.
Chemical: Spot applications of glyphosate at 1.5% v/v timed
at the early flowering stage have been effective. Fall applications are also
recommended. Glyphosate can also be successfully integrated with mowing and
applied directly to the tops of cut stems in a 20-30% solution with a wick applicator.
One important issue with glyphosate is injury to desirable vegetation. Purple
loosestrife is highly competitive and will rapidly reinfest open areas. Therefore,
it is important to minimize injury to desirable vegetation surrounding infestations.
It may not be necessary to completely wet all of the foliage to kill the plant.
However, wetting at least 25% of the foliage is recommended.
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