P EST N OTES Publication 74130
University of California
Agriculture and Natural Resources May 2006
C OMMON G ROUNDSEL
Integrated Pest Management for Home Gardeners and Landscape Professionals
Common groundsel or old-man-of-the-
spring (Senecio vulgaris) is found nearly
everywhere in California (Fig. 1). It is
most prolific during the cooler times of
the year, but can be found year-round
near the coast or in shady areas. Al -
though common groundsel grows
best in moist fertile soil, it can grow
in more trying environments such as
along roadsides and other disturbed
sites. It is also one of the major weeds
in nurseries. It is a competitive plant in
landscaped areas and gardens, but it is
generally not a problem in lawns. In ad -
dition to the general weediness of this
plant, it also can cause chronic liver
poisoning to horses, cattle, and swine,
even if only a small amount is eaten
over a few weeks time.
The success of common groundsel as
a weed lies in its seeds. It starts devel -
oping seeds very early in its life cycle
and can produce 25,000 or more seeds
per plant under optimal conditions,
although about 1,700 seeds per plant
are more likely. These seeds are easily
spread by wind. Additionally, there can
be three or more generations per year.
Even when the plant is pulled from the
ground or cut down, seeds from open
flowers can still mature and germinate.
This weed was also one of the first to
have populations develop resistance to
some common agricultural herbicides.
IDENTIFICATION
AND LIFE CYCLE
Common groundsel is in the Astera -
ceae family, which also includes sun -
flower, dandelion, and thistles. It is
classified as a winter annual since the
seeds germinate in late fall through
early spring. The plant matures
throughout spring and early summer
and usually dies in the summer heat.
The first true leaves of seedlings have
shallow teeth, may be purple on the
underside, and are attached to the stem
with a short petiole. Later developing
leaves are more deeply lobed and are
attached directly to the stem. Leaves
alternate on the stem and are mostly
hairless. In full sun, groundsel grows
up to 2-feet tall with a shallow taproot
and a secondary fibrous root system
and is often branched. Under shaded
conditions the mature plant will have
a scraggly appearance with fewer and
smaller leaves.
Flowers generally form about 6 weeks
from sprouting. Flower clusters are
surrounded by green bracts with black
tips. This characteristic black tip distin -
guishes common groundsel from other
plants in the Asteraceae family (Fig. 2).
Flowers are bright yellow and when
Figure 1. Common groundsel or old-man-of-the-spring (Senecio vulgar is) . A. receptacle showing a single flower; B. achene (seed).
A. B.
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May 2006 Common Groundsel
the seeds mature, the bracts fully open
to reveal a ball of white-tufted seeds.
These seeds are easily dislodged and
carried by wind. Under good growth
conditions the plant can produce
numerous flowers. When growing in
shade or other stressful conditions the
plant may only produce a few flower
heads.
IMPACT
Because common groundsel produces
so many seeds and the seeds are eas -
ily spread, it can rapidly produce an
unsightly infestation in landscape beds.
In flower and vegetable gardens, early
emerging common groundsel plants
can out-compete later emerging crop
seedlings and reduce their growth.
Common groundsel plants that emerge
after the crop is established are not ef -
fective competitors and have less of an
impact. The most harmful consequence
of the weed is liver poisoning of live -
stock. It is important to control com -
mon groundsel in and around areas
where livestock may graze.
MANAGEMENT
Common groundsel is best controlled
by eliminating the plant before it flow -
ers. Since seeds can still mature even
if the plant itself is killed, it is impera -
tive to remove the plant from the area
if there is any evidence of flowering.
Seeds of common groundsel are not
long-lived, usually remaining viable
for about one year. Therefore, control -
ling this weed before flowering will
have a great impact on the size of the
next year’s population.
Shallow tilling or hoeing of young
plants effectively controls common
groundsel. Start monitoring for seed -
lings in early fall and remove seed -
lings and plants as soon as possible.
Monitoring should continue through
early summer. Even if all the weeds
in your garden are controlled, com -
mon groundsel may still infest the
area from seeds that are blown in from
nearby sites.
Cultural
and Mechanical Control
In most situations, common groundsel
is easily controlled by hand removal
or cutting the plant off at its taproot
by hoeing. Monitoring the area on
a regular basis and removing the
weed throughout the growing season
will greatly reduce the impact of the
weed the next year. In larger areas,
rototilling of young plants is effective.
Mowing can be effective if the blade is
set as close to the ground as possible.
Mulches are very effective for control -
ling common groundsel. Seedlings
cannot push through a 3-inch deep
layer of mulch. Blown in seeds can -
not establish on mulch if the surface
is allowed to dry out. The key to con -
trol when using mulches is to choose
a mulch size that is large enough
to allow water to pass through and
the mulch surface to dry out. This is
best accomplished by using coarse
mulch, usually sold as medium size.
Fine mulch such as sawdust and pot -
ting compost will absorb water and
actually become a suitable site for the
common groundsel seeds to establish.
Using mulch that has large pieces is
also not recommended because these
types will have too much space be -
tween the pieces. Seeds can drop to the
soil underneath and grow up between
the spaces. Synthetic mulches, such as
landscape fabrics, provide a physical
barrier to seedling development. How -
ever, these are only effective for control -
ling seeds that are already in the soil.
They will not be effective in controlling
seeds that have blown in during the
current growing season.
Biological Control
The most promising method of biologi -
cal control is the use of the rust fungus
Puccinia lagenophorae. This fungus pro -
vided about 30% control in greenhouse
tests. Research is being conducted to
find ways to improve its efficacy. There
are no insects that are effective for con -
trolling common groundsel.
Chemical Control
Common groundsel in the home
garden and landscape is best con -
trolled using cultural and mechanical
methods. If these methods cannot be
used, herbicides containing diquat or
glyphosate will control growing plants
in home landscape beds. Only glypho -
sate can be used around edible crops
and it will severely injure or kill any
plant it touches. The sprayer tip should
be shielded so that the spray does not
contact any desirable plants, as either of
these herbicides will injure many orna -
mental plants. There are no preemer -
gent (before the plant emerges from
the soil) chemical controls available for
home use that are effective for control -
ling common groundsel.
REFERENCES
Fischer, B. 1998. Grower’s Weed Identifica -
tion Handbook. Oakland: Univ. Calif. Div.
Agri. Nat. Res. Publ. 4030.
Parchoma, G., ed. 2002. A Guide to Weeds
in British Columbia. British Columbia:
British Columbia Ministry of Agricul -
ture, Food and Fisheries. Also available
online, http://www.weedsbc.ca/pdf/
GuidetoWeeds.pdf.
University of California Statewide IPM
Program. Integrated Pest Management
Weed Photo Gallery, an online photo -
graphic reference to many weeds com -
monly found in California. Available
online, http://www.ipm.ucdavis.edu/
PMG/WEEDS/common_groundsel.
html. Accessed May 23, 2006 ❖
Figure 2. Bracts at the base of the common groundsel flower have black tips, distinguishing this species from common sowthistle and other plants in the Asteraceae family.
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May 2006 Common Groundsel
WARNING ON THE USE OF CHEMICALS Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed, away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits or vegetables ready to be picked. Do not place containers containing pesticide in the trash or pour pesticides down sink or toilet. Either use the pesticide according to the label or take unwanted pesticides to a Household Hazardous Waste Collection site. Contact your county agricultural commissioner for additional information on safe container disposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers by following label directions. Never reuse or burn the containers or dispose of them in such a manner that they may contaminate water supplies or natural waterways.
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AUTHORS: C. A. Wilen, UC IPM Statewide Program, San Diego Co.TECHNICAL EDITOR: M. L. FlintCOORDINATION & PRODUCTION: P. N. Galin ILLUSTRATIONS: Fig. 1: W. Coover. Weeds of California. 1941. California State Dept. of Agric; Fig. 2: W. Suckow
Produced by IPM Education & Publications, UC Statewide IPM Program, University of California, Davis, CA 95616-8620
This Pest Note is available on the World Wide Web (www.ipm.ucdavis.edu)
This publication has been anonymously peer reviewed for technical accuracy by University of California scientists and other qualified profession - als. This review process was managed by the ANR Associate Editor for Pest Management. To simplify information, trade names of products have been used. No endorsement of named products is intended, nor is criticism implied of similar products that are not mentioned. This material is partially based upon work supported by the Extension Service, U.S. Department of Agriculture, under special project Section 3(d), Integrated Pest Management.
