Buckthorn species are wild
hosts of spotted wing drosophila
The OMAFRA spotted wing drosophila (SWD) team learned a lot about
SWD in 2012. Not only did the SWD spread rapidly throughout Ontario,
but it was also found on a new wild host, common buckthorn (also
known as European buckthorn) which is considered an invasive plant.
How to identify common buckthorn
- Buckthorn is usually the first shrub to leaf out in the spring
and the last to drop its leaves late in the fall.
- It often grows 2 to 3 meters tall. Occasionally it reaches 6
meters, with a trunk up to 25 centimeters in diameter.
- It is distinguished by the sharp, thorn-tipped branches in contrast
to the simple or compound thorns growing from the sides of branches
in the Hawthorns.
- It has smooth, dark green leaves that are finely toothed, 2.5
to 6 centimeters long, with prominent forward-curved side veins,
arranged in opposing pairs along the stem.
- It produces clusters of purplish-black berries along the stems
and short twigs, and each berry usually has 4 hard seeds.
Impacts of common buckthorn
- The shrub can be an alternate host for spotted wing drosophilia,
a fruit fly that has become a widespread pest of soft-skinned
fruits in Ontario.
- The shrub can host oat rust, a fungus that causes leaf and crown
rust and affects the yield and quality of oats.
- The soybean aphid, an insect that damages soybean crops, can
use buckthorn as a host plant to survive the winter.
- Because it can affect agricultural crops, common buckthorn is
listed as a noxious weed under Ontario's Weed Control Act.
How to control common buckthorn
- A variety of mechanical control methods can be used to kill
or remove buckthorn and other non-native plants.
- Cutting buckthorn shrubs has limited effectiveness because
the plant resprouts.
- Girdling involves cutting the phloem (inner bark) but leaving
the xylem (sapwood) intact. The roots nourish the top, but
the top sends no nourishment back to the roots, which die
out. Girdling is most effective in late spring or early summer
(DNR WI). The shrub takes a year or two to die (Packard 1997).
- Seedlings or small plants may be hand pulled or removed
with a hoe and will not resprout. Larger plants (1-6 cm in
diameter) may be pulled out with heavy equipment. Disturbed
soil will result from these techniques and should be tramped
down to minimize exposing new buckthorn seeds (DNR WI). This
technique may be most useful to control low densities.
- Land managers have had mixed results with the use of prescribed
fire to control buckthorn species. Fire does not spread readily
through buckthorn thickets and the buckthorn resprouts following
burns, especially if moisture is available.
- Chemical control methods are best done during the fall or winter
when most native plants are dormant yet buckthorns are still actively
- Herbicide application to buckthorn seedlings has been shown
to be effective. The best time to spray the foliage is very
early in the spring, before native plants leaf out or later
in the fall, after native plants drop their leaves. Common
buckthorn is the first shrub to leaf out in the spring and
the last plant to drop its leaves in the fall.
- Applying chemical (e.g. Garlon 4, glyphosate) to a recently
cut stump is usually quite effective at killing buckthorns
and minimizes the amount of chemical used. Shrubs can be cut
using hand tools, chain saws or brush cutters and should be
cut close to the ground. Chemical must be applied to freshly
cut stumps to be effective. The chemical can be applied by
paint brush or squirt bottle. Some chemicals must be applied
to the remaining bark as well. Stump treatment can be carried
out throughout the growing and dormant season. Dye should
be added to mark the treated stumps.
- Basal bark treatment is a method that applies chemical on
the bark of a standing tree/shrub. The chemical and its binding
agent are absorbed through the bark into the plant, where
it kills the living cambium.
- Frilling involves killing a standing tree by applying herbicide
to a gash cut in the bark. The tree is gashed with an axe
or chain saw and the herbicide is applied directly in the
gash, killing the tree immediately. While this method requires
a little more time than basal bark treatment, it is generally
more effective as the chemical is applied directly to the
growing parts of the standing trunk. This technique may be
the most effective method to kill large buckthorn trees.
Table 1. Sample of chemical trials that successfully controlled
From: Upper Grand River Conservation Authority Factsheet
|Cut Stump Application
|20 - 25% glyphosate (diluted in water)
||August or September
|12.5% tricolopyr (form for oil dilution)
||Summer or winter
|Garlon 4 (1:3 of Garlon 4:oil/diluent)
|4% ester with diesel
|AMS, aqueous concentrated
|25% Picloram + 75% 2,4-D
||25% Picloram + 75% 2,4-D
|Basal Bark Application
||2-4% ester 2,4-D in diesel
||May to June
|10-20% Garlon in diesel fuel
|Glyphosate (e.g. Roundup)
Note: Some trade name chemicals are not available
Figure 1. Common buckthorn leaf characteristics
Figure 2. Common buckthorn distinguishing thorn at the end of
Figure 3. Common buckthorn berries
Figure 4. Common buckthorn in field margin understory
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