Wild marigold [Tagetes
minuta L.][TAGMI][CDFA list: A] Photographs
Map of Distribution
SYNONYMS:tagetes, stinking roger, khaki weed
DESCRIPTION:An erect summer annual,
to 1 m tall. Resembles, but is less showy than the garden marigold (Tagetes
erecta L.). Wild marigold is a problematic weed of pastures and
numerous crops in East and South Africa, South America, and Australia. The
seed has an unpleasant odor and can reduce the value of grain harvests when
it is a contaminant. Introduced from western South America, where it is used
medicinally, as a condiment, and for herbal tea. Commercially grown in Brazil
and other countries for the oil, which is used in perfumes and for flavoring
numerous food products. Some evidence suggests that the secondary compounds
are inhibitory to parasitic root nematodes and other microbes. Wild marigold
is sometimes an alternative host for Sclerotinia sclerotiorum, a fungal
pathogen that can infect a variety of crops.
SEEDLINGS:No description available, but probably resemble garden marigold
PLANT:Foliage pungent, glabrous,
dotted with embedded translucent glands. Leaves once-pinnately compound
or divided, opposite below, alternate or opposite above, 5-15 cm
long. Leaflets 11-17, narrowly lanceolate, sharply toothed (serrate), 2-4
and UNDERGROUND STRUCTURES:Taprooted. Forms
FLOWERS:Spring-summer. Inflorescences panicle-like (cymes), +/- flat-topped,
consist of numerous narrowly cylindrical flower heads, 7-10
mm long and ~ 3-4 mm in diameter. Phyllaries 3-5, in a single
series and fused into a tube, dotted with glands, not splitting
apart at maturity. Ray and disk flowers barely extend beyond the
phyllaries. Ray flowers 1-5, pale yellow. Disk flowers 3-5, yellow to
orange-yellow. Receptacles lack chaffy bracts.
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and SEEDS:Achenes cylindrical, 4.5-7 mm
long, dark brown. Pappus consists of 1-2 (unequal) awn-like scales, 2-3 mm
long, and 3-5 ovate to lanceolate scales, 0.5-1 mm long, +/- fused.
HABITAT:Colonizes disturbed sites, especially cultivated or previously
cultivated sites and orchards where wild marigold was planted to control nematodes.
Tolerates low to high rainfall and elevations.
DISTRIBUTION:Southern Sierra Nevada foothills, southern San Joaquin Valley
(Tulare Co.). Previous infestations now eradicated in southern South Coast
Ranges, western Transverse Ranges (sw Santa Barbara Co.), and San Francisco
Bay region (e San Mateo, nw Santa Clara cos.). To 1000 m (3300 ft).
PROPAGATION/PHENOLOGY:Reproduces by seed. Seed germination requires light,
and most seed germinates between 20 and 30º C (optimal 25º C). Fresh
seed lacks a dormancy period and germinates within 7 days of imbibing water.
Seed imbibed at high temperatures for several days or dried out and reimbibed
can germinate at an accelerated rate when temperature becomes near optimal.
Seed often germinates on the soil surface and most seedlings emerge from soil
depths of less than 6 mm.
cultivation or manual removal before flowers mature discourages survival.
Populations can increase significantly after a burn.
SPECIES:Unlike wild marigold, garden
varieties of marigold have showy flower heads larger than 10 mm long and 4
mm in diameter. Fetid marigold [Dyssodia papposa (Vent.) A.
Hitchcock][DYSPA], an unpleasant smelling annual introduced from central and
eastern North America, has separate phyllaries in 2-3 series and flower
heads 4-10 mm in diameter. It is a weed of roadsides and disturbed sites in
the eastern South Coast region (sw San Bernardino Co.). To 350 m (1150 ft).
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Prevention: Wild marigold is a
native annual of Central and South America that has become a major agricultural
weed in 35 countries worldwide. It has been detected in Tulare County, California
and is considered a CDFA class A noxious weed. Wild marigold is a prolific
seed producer (>29,000 seeds per plant) that may aggressively colonize
waste areas, neglected rangeland, or poorly managed agricultural fields. Plants
may reach a height of 2 m and effectively outcompete many desirable plants
for light, moisture, and nutrients. The plants are strongly aromatic and have
been used for teas and other medicinal purposes. Root extracts are allelopathic
to many vegetables, corn, and sunflowers. Wild marigold is found in numerous
habitats over a range of moisture regimes and elevations. If uncontrolled,
it may rapidly expand its range in California. In Africa, the primary mechanism
of seed dispersal is contaminated crop seed. Prevent new infestations by planting
only certified weed free crop seed, and cleaning tillage equipment between
Mechanical: In agricultural fields,
cultivation is very effective in controlling wild marigold. However, new seedlings
will rapidly germinate where the crop canopy does not shade the soil surface.
Seed buried below a depth of 6 mm remain dormant. However, the persistence
of wild marigold seed in the soil has not been determined.
Biological: There are no biological
control agents for wild marigold. Livestock will consume it, but generally
only when no other forages are available. Seed dispersal through animals is
likely, but has not been extensively studied.
Burning: There is little information
evaluating fire as a control strategy for wild marigold. However, observations
from East Africa have shown that wild marigold is apparently favored in areas
following fires or other land-clearing operations. This supports other research
that has demonstrated its ability to dominate in highly fertile environments.
Known infestations should be closely monitored following fires, as proliferation
Chemical: In agricultural fields,
most preemergent herbicides are effective in controlling wild marigold. However,
late season control may be reduced if herbicides leach below the germination
zone. This may occur more readily on sandy, light textured soils.
In rangeland areas, 2,4-D, 2,4-DB, MCPA, and dicamba are effective on seedlings.
However, late season flushes will not be controlled, and reapplication may
be required. Although data is lacking, glyphosate clopyralid, and triclopyr
may also be effective.