Leafy Spurge
Biology and Management
Jerry Doll
Leafy spurge (Euphorbia esula
L.) is a deep rooted perennial broadleaf weed found in
right-of-ways, wastelands, parks and some pastures. Years ago it
was declared a noxious weed in Wisconsin in recognition of (1)
its potential to become a widespread and serious weed problem,
(2) the limited area of infestation at the time and (3) the
great difficulty of controlling it in extensive areas.
Classification as a noxious weed may have slowed its spread in
the state but certainly has not eradicated leafy spurge. It is
now encroaching into new areas in several regions. Infestations
are most noticeable along roadsides and now often spread into
adjacent pastures and other non-disturbed sites. We need to take
appropriate measures to prevent leafy spurge from becoming more
widespread.
Origin &
Distribution
Leafy spurge is a native to Europe and
Asia where it is seldom a weed of economic importance. It was
found in Massachusetts in 1827 and in North Dakota in 1909 and
probably reached Wisconsin also in the early 1900s. The greatest
abundance of the weed is in the northern great plains of the
United States and the prairie provinces of Canada. In North Dakota
alone it infests more than 900,000 acres, is found in every county
in the state. Direct and indirect business losses exceed $86
million per year in North Dakota, including an $8 million loss in
this state’s wildlands (Leitch et al 1994). These losses occur
because leafy spurge displaces desirable forages and is not
consumed by livestock nor wildlife animals. All plant parts
contain a milky sap which can cause severe irritation to human
skin and sickness to livestock if consumed. It is also a vigorous
competitor with crops if found in cultivated land.
Description &
Biology
Plants are long-lived, deep-rooted
perennials that spread by an extensive root system and also by
seeds. Figure 1 shows the general nature of the plant and enlarged
views of flowers, bracts, fruits and a root with buds. Roots are
tough and woody with numerous buds capable of producing stems.
Both long and short roots are formed. Long roots have extensive
lateral growth and give rise to the shoot buds that account for
the vegetative spread of leafy spurge patches. Some roots may
penetrate to 12 feet deep. Short roots arise from the long roots,
have no shoot buds, and are important for water and nutrient
uptake.
Vegetative buds occur on both
the roots and underground portions of shoots. They are pink
colored and found from 1 to 68 inches below the soil surface,
and a single root may have 35 to 277 buds, with the greatest
numbers just below the soil surface. Only a few buds actually
develop shoots; the majority remain dormant and sprout when old
shoots are weakened or killed. New shoots are capable of
emerging through 2 feet of soil and occasionally from 3 feet.
Upon reaching the soil surface, new crowns are formed which then
regrow into new plants in following years. Thus, chemical or
mechanical control must kill buds to at least 3 feet deep to
prevent leafy spurge reestablishment.
Stems are 1½ to 3 feet tall
and unbranched (except for the inflorescence). Buds in the leaf
axils may form shoots if the stem tip is injured or cut. Stems
are woody near the base, light green during the summer and turn
yellow or reddish by the fall. Solid stands have approximately
165 stems/sq yd but much higher densities have been recorded.
The main stem is usually surrounded by 8 to 10 secondary stems
from the same crown, giving plants a clump-like appearance. Leaves
are bluish-green to dull green, generally alternate but some may
appear to be opposite (two per node), 1.5 to 3 inches long,
linear to wedge-shaped and have a whorl of 7 or more leaves at
the stem tips below the inflorescence. Plants often become light
green during the summer.
The inflorescence has
numerous greenish flowers in umbel-like clusters with 7 or more
branches in the tip of the main stem and in smaller branching
clusters at the tips of secondary stems. One of the more
conspicuous features of the inflorescence are the bracts
(modified leaves) at the base of each flower. They are yellowish
in color, kidney-shaped and usually have pointed tips. While
they are the most colorful part of the plant, they are not true
flower parts.
Flowers are tiny, unisexual
with 11 to 20 male flowers and a single female flower crowded
into a structure typical of the spurge family known as the
cyanthium. After the female flowers open, glands at the base of
the cyanthium begin secreting nectar. Then the male flowers
develop and pollination is done by insects as they feed on the
nectar. Flowering starts in mid to late May and is completed in
the main stems by late June to July. Some flowering also occurs
in late August and September. The fruits are 3-celled but
about half contain only one seed, 35% may have two seeds and the
remainder form three seeds per fruit. The seed pods explode when
ripe, shooting the seeds up to 15 feet away. Each inflorescence
produces 10 to 50 fruits with 25 to 150 seeds.
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Seeds
are relatively large, with a prominent yellow-colored bump at
the narrow end. A brown line extends from one end of the seed to
the other. Color varies from grayish-white to grayish-brown and
seed coats usually have brownish spots throughout. Most seeds
germinate or decay within two seasons; no seeds survive more
than 8 years in the soil. Seeds germinate when air temperatures
reach 78 to 82o F. Most emerge from .5 to 2 inches
deep but they can emerge from 4 inches.
Once seedling plants have six or
more leaves, most are capable of regrowing if stems are cut,
which means that they are now perennial, capable of vegetative
reproduction. By the 10-leaf stage, all plants originating from
seed behave as perennials. Within 90 days after emergence,
vegetative buds are found on the roots. A crown of buds forms at
or just below the soil line of both the main stem and those
arising from lateral roots. Within 16 months, a single plant can
produce a 5-ft vertical root, 32 feet of lateral roots, 70 feet
of branch roots and over 1700 buds! In four years, a single
plant can spread to 18 feet in diameter above ground and 24 feet
below ground. A patch of 7 square feet may spread to cover 2700
square feet in 5 years. Thus, if left unchecked, leafy spurge
has a tremendous ability to invade field pastures and
non-cropland areas.
In most years, leafy spurge
plants resume active growth in southern Wisconsin by the end of
March but this varies from early March to early April with the
severity and length of the winter season. Plants flower rather
consistently in mid May (Doll, 2001).
Management
Cultural. Prevent leafy spurge
from producing seed if possible. Mowing as plants begin to flower
is highly recommended and would be the least one could do to
comply with our noxious weed law. A second mowing will give even
greater assurance that no new seeds are added to the seed bank.
Clean mowers before leaving infested pastures so that leafy spurge
and other weed seeds are not spread to other sites. Do not harvest
grass hay from pastures infested with leafy spurge that has viable
seeds.
Fortunately, in Wisconsin, most land
managers face only isolated patches of leafy spurge and the total
control cost per operating unit or farm should not be prohibitive.
However, the longer one waits to initiate control measures,
naturally the more expensive the battle becomes.
Mechanical. Plants store a 2-
to 3-year food supply in the root system but leafy spurge can be
nearly eradicated by repeated cultivation for two years. Till
infested areas to 3 to 4 inches deep each time plants are 3 to 4
inches tall which may be as often as every 2 weeks under favorable
growing conditions. Continue cultivating until late fall. Try to
avoid spreading root pieces and seeds to uninfested areas and
fields. Tillage is most effective when done in dry soil as the
roots are killed when exposed to 96o F temperatures in
the soil. Such intensive cultivation is impractical and
uneconomical in most situations.
Chemical. No product will
eliminate leafy spurge infestations in a single season due to the
depth and density of the roots and the reserve of seeds in the
soil. The long term effectiveness of any treatment will depend in
large measure on having a competitive mix of desired species to
further displace treated plants and also prevent the
reestablishment from germinating seeds. Herbicides that have
activity on leafy spurge are presented below, along with an
indication of how these products fit into the Wisconsin landscape.
Non-crop areas.
The literature shows that picloram
(Tordon) is among the most effective products for leafy spurge.
Lym (1999) applied picloram, 2,4-D and the combination of these
for 10 consecutive years to leafy spurge in North Dakota (Table
1). Control was generally superior with the tank mix of picloram
and 2,4-D for the first 8 yr but both this combination and
picloram alone gave 98% control by the 10th year
compared to 80% for two annual applications of 2,4-D alone. Four
years after the last application, these treatments still averaged
90% spurge control compared to only 28% for 2,4-D alone.
Table 1. Long-term study
of leafy spurge control with annual herbicide applications in
North Dakota (Lym 1998 and 1999.)
|
 |
| Years
after the first treatment |
Number
of years without treatment |
|
Herbicide |
1 |
3 |
6 |
8 |
10 |
3 |
4 |
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-------------------------%------------------------ |
| Tordon
(picloram) |
56 |
60 |
59 |
70 |
98 |
88 |
86 |
| 2,4-D (twice/year) |
21 |
30 |
55 |
64 |
80 |
24 |
28 |
| Tordon
+ 2,4-D |
68 |
74 |
79 |
84 |
98 |
89 |
94 |
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We have serious limitations and
concerns regarding picloram use in Wisconsin. First, it is
illegal to use picloram in pastures or cropland in Wisconsin.
This is because the active ingredient is very soluble and
persistent and presents serious risks of ground and surface
water contamination if used in large quantities over large
areas. Drift to adjacent vegetation would cause serious crop or
ornamental plant injury and its persistence in the soil (2 to 3
yr or more) seriously limits crop rotations. Picloram can be
legally used in right-of-ways and forests in our state but we
caution against its use unless every assurance of environmental
protection can be made.
Newer chemistries have also proven
to be effective in controlling leafy spurge. Lym has pioneered
this research as well. He and his team have evaluated quinclorac
(Paramount) and imazapic (Plateau) for many years and both give
very acceptable results with minimal risk to the environment or
adjacent vegetation. Paramount is most effective when applied in
either the summer or early fall and is very safe to perennial
grasses while Plateau is most effective as an early fall
treatment and can temporarily injure perennial grasses,
especially the cool season species. Paramount is not available
in Wisconsin at this time so I will present only limited data on
this product. See the paper by Kuehl and Lym (1997) for
additional information on leafy spurge control by quinclorac.
Plateau is most effective when applied
in the early fall. Table 2 shows that summer treatments of
imazapic averaged 72% leafy spurge control while fall applications
averaged 89%. The label recommends treatments be made from late
August to mid-October and before a killing frost. Markle and Lym
(2001) applied imazapic on five dates from mid-August to
mid-October and found that Sept. 15 gave the best leafy spurge
control in North Dakota.
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Table 2.
Plateau (imazapic)
applied in the summer and fall for leafy spurge control (Lym
1998-2000).
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|
Fall
Control |
|
1997 |
1998 |
1999 |
2000 |
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------------------------------------%------------------------------------- |
Summer-applied
(96, 97, 98) |
59 |
89 |
81 |
57 |
Fall-applied
(96, 97, 98) |
94 |
91 |
95 |
77 |
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One of the other discoveries by Lym’s
team was that diflufenzopyr (a component of the herbicide
Distinct) enhances the activity of systemic herbicides on leafy
spurge (Table 3). The magnitude of the response varied between
sites and years but was consistent and usually significant. They
found little if any correlation between diflufenzopyr ratio with
other herbicides and the enhancement in performance. The ratios
tested ranged from 2.5:1 to 10:1 of the leafy spurge herbicide
to diflufenzopyr; the ratio of dicamba to diflufenzopyr in
Distinct is 2.5:1. For that reason, the research we started in
1999 in Wisconsin included Distinct as a tank mix with Plateau
and Paramount to enhance their activity on leafy spurge.
Distinct is labeled for use in non-crop site, and it is legal to
use in tank mixes with Paramount and Plateau for leafy spurge
control. |
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Table 3. Diflufenzopyr
to enhance leafy spurge control from systemic herbicides
(summary of several trails reported by Lym 1998-2000).
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Our trials on leafy spurge
management began at Ft. McCoy in 1999 and include early summer
applications of Paramount and early fall applications of
Plateau; Distinct and the recommended additives were included
with both products. The objective is to compare the performance
of these products when applied once, twice or three times on
leafy spurge. The second and third applications are done on an
"as needed basis" and this is determined by counting
spurge stems in each plot twice a year. Treatments are made at
two sites at Ft. McCoy; both are managed as native prairies and
have moderate to high leafy spurge populations. The State
Natural Area was burned in April 1999 and the Badger Drop Area
was burned in April 2001.
Tables 4 and 5 show spurge
populations through the fall of 2001. The populations on 5/99
were taken before any treatments were made. A single application
of Paramount in 1999 suppressed spurge at the Badger Drop site
until the spring of 2001. The burn in 2001 allowed (caused?)
leafy spurge seeds to germinate and perhaps cleared the way for
buds on roots to sprout because the mulch was gone and warm
season grasses do not produce new growth until well after leafy
spurge has emerged and developed. Spurge populations are higher
at the State Natural Area as there is less grass present and the
second Paramount was needed in the two and three application
systems in 2000; these systems have suppressed leafy spurge
through the fall of 2001 with the exception of the 2001
application at the State Natural Area. This is probably due to
the lack of a dense grass stand and the reduction in the rate of
Paramount labeled for use in leafy spurge. In 1999 and 2000, we
applied Paramount at 12 oz/a; the current labeled rate is 8 oz/a
and this rate was used in 2001.
The fall 1999 treatment of Plateau
gave outstanding leafy spurge control at both sites (Table 5).
No additional treatments were made at the Badger Drop Area until
2001 (following the burn of that year) while a second
application was made to two treatments at the Natural Area in
2000; this again reflects the lack of a competitive stand of
desired species at this site which allows spurge to reinfest.
Research at Ft. McCoy will continue for several years.
In summary, when leafy spurge
appears in non-crop sites, Plateau would seem to be the product
of choice. Treat from mid to late September and use the
recommended additives. You may wish to include Distinct with
Plateau in some or all of the areas treated to see if
differences are noted.
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Table 4.
Long-term management
of leafy spurge with Paramount (quinclorac) at Ft. McCoy,
Wisconsin1.
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Table 5. Long-term
management of leafy spurge with Plateau (imazapic) at Ft. McCoy,
Wisconsin1.
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| Site |
Plateau
applied |
Leafy
spurge population (stems/11 sq. ft.) |
| 5/99 |
5/00 |
6/01 |
9/01 |
|
| Badger
Drop Area2 |
Fall
99 |
345 |
9 |
580 |
340 |
| Fall 99 & 01 |
580 |
0 |
350 |
385 |
| Fall
99, 01, & ?? |
305 |
0 |
200 |
200 |
| State
Natural Area3 |
Fall 99 |
1625 |
45 |
1505 |
1195 |
| Fall
99 & 00 |
275 |
0 |
350 |
295 |
| Fall 99, 00
& ?? |
1140 |
0 |
0 |
70 |
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1
All treatments applied with 2 oz/a Distinct to have
diflufenzopyr in the treatment. Plateau rate was 8 fl oz/acre
of the liquid formulation of Plateau for all treatment dates.
2
This area was not burned in 1999 or 2000 but was burned in
April, 2001. It has moderate to good grass and forb coverage
(Avg. of 82%). There are two replications here.
3
This area was burned in April 1999 but has not been burned
since. It has poor grass and forb coverage (Avg. of 46%). We
have only one plot per treatment at this site. |
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In pastures and CRP sites. We
have no effective herbicides that can be used to selectively
control leafy spurge in pastures in Wisconsin. Fortunately, this
weed is not commonly found in pastures. If it does appear,
consider spot applications of glyphosate and then reseed the
treated areas. Using tillage as part of the reestablishment
program will improve the kill of leafy spurge roots. However, it
may also allow spurge seeds to germinate. If this happens, apply
2,4-D or dicamba while leafy spurge plants are still seedlings
(within 30 to 45 days of emergence).
In CRP sites, leafy spurge should be
mowed at least twice annually. Check with your NRCS office to
determine allowed mowing times and to request an exemption if
necessary. Because leafy spurge is a legally declared noxious
weed in Wisconsin, mowing these sites to prevent seed production
should be allowed. Plateau is not a practical option in CRP land
as the rate for these sites is half of that recommended for
leafy spurge control. If a CRP site is being brought back into
production, then a fall application of glyphosate followed by a
crop of glyphosate resistant soybean or corn is suggested.
In cropland. In the unlikely
event that leafy spurge infests cropland, the advent of
glyphosate resistant soybean varieties and corn hybrids opens an
entirely new avenue of leafy spurge control. Based on research
with other perennial broadleaf weeds, we recommend planting
soybean or corn without tillage, use a burndown herbicide to
kill early emerging weeds and add a reduced rate of a
soil-active herbicide to suppress annual weeds, and apply
glyphosate in the glyphosate resistant crop when leafy spurge is
in the early flowering growth stage. In situations where
conventional varieties are grown, vigorous tillage before
planting and row cultivation in either corn or soybeans should
give adequate spurge suppression.
Biological Control. Several
insects are known to suppress leafy spurge. Some states in the
Plains region have successfully reduced spurge infestations
using flea beetles (Aphthona spp.) whose larvae attack
leafy spurge roots. Insect populations often increase rapidly
after release at spurge-infested sites and near eradication of
leafy spurge within a few years of release has occurred at some
sites (Lym and Nelson, 2000). Releases in Wisconsin have not
been as spectacular. Nevertheless, efforts to have natural
enemies attack leafy spurge in Wisconsin continue and hopefully
they will succeed in the future.
As always, integrated control
is essential to get the best control of a tough perennial weed
like leafy spurge. Efforts taken now will certainly minimize the
potential magnitude of the problem in future years.
References
Derscheid, L. and L. Wrage. 1980.
Leafy spurge. S. Dak. State Univ. Exten. Bull. FS-499. 4p.
Doll, J. D. 2001. Knowing when to
look for what: weed emergence and flowering sequences in
Wisconsin. Proc. Wis. Fert., AgLime & Pest Management Conf.
40: 96-103.
Gylling, S. and W. Arnold. 1985.
Efficiency and Economics of Leafy Spurge Control in Pastures.
Weed Science 33:381-385.
Kinch, R.C., L. Wrage and R.A.
Moore. 1975. South Dakota Weeds. South Dak. State Univ. Ag Exten.
Ser. 228 p.
Kuehl, B.D. and R.G. Lym. 1997.
Leafy spurge control with quinclorac. Weed Tech. 11:265-269.
Lym, R.G. 1999. North Dakota
State Univ. Weed Control Research. 22 p.
Lym, R.G. 2000. North Dakota
State Univ. Weed Control Research. 18 p.
Lym, R.G. and J.A. Nelson. 2000.
Biological control of leafy spurge with Aphthona spp.
along railroad right-of-ways. Weed Tech. 14:642-646.
Lym, R.G. and D. Van der Puy.
1985. Leafy Spurge (Euphorbia esula L.). North Dakota
State Univ. Exten. Bulletin 14AGR-12. 2p.
Markle, D.M. and R.G. Lym. 2001.
Leafy spurge control and herbage production with imazapic. Weed
Tech. 15:474-480.
The March-April, 1983 issue of
North Dakota Farm Research (Vol. 4, No. 5) has these excellent
articles on leafy spurge:
Messersmith, C. 1983. The Leafy
Spurge Plant. pp. 3-7.
Messersmith, C. and R G. Lym.
1983. Distribution and Economic Impacts of Leafy Spurge in North
Dakota. pp. 8-13.
Lym, R.G. and C. Messersmith.
1983. Control of Leafy Spurge with Herbicides. pp.16-19.
Galitz, D. and D. Davis. 1983.
Leafy Spurge Physiology and Anatomy. pp. 20-26.
December 2001
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