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Frequently Asked Questions (FAQ)
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Biological Control
Q: Where do flea beetles come from?
A: Aphthona
flea beetles are natives of Europe and Asia, and are widely dispersed across
a large geographic area – they’re found as far east as China and as far west
as France. There is also a North American leafy spurge flea beetle, but it
appears to have relatively little impact on leafy spurge. Ironically, leafy
spurge is generally not a problem in its native lands, where flea beetles
and other enemies maintain infestations at economically unimportant levels.
In fact, entomologists looking for new biocontrol agents overseas often have
difficulty finding large patches of spurge.
Q: Will flea beetles eat crops or
other economically valuable plants if they run out of leafy spurge?
A: No. All imported biocontrol agents, including Aphthona flea
beetles, are quarantined and rigorously tested before being imported and
released. If any potential for damage to crops or economically important
plants is identified during this process, the candidate agent will not be
approved or imported. This process has shown that Aphthona flea
beetles are very host-specific and feed only on a narrow range of hosts
restricted to the spurge family. We will soon have a page giving the
step-by-step description of the quarantine and host-specificity testing
process so be sure to come back for new pages and updates.
Q: What about other leafy spurge
biocontrol agents?
A: To date, 15 different insects (including six different
Aphthona flea beetles) have been tested, approved and released for
biological control of leafy spurge. Significant success at controlling leafy
spurge, however, has been achieved by only the A. nigriscutis and
A. lacertosa flea beetles. Other insects have either failed to establish
populations, or have established limited populations that have not had a
significant impact on spurge infestations. Following are brief descriptions
for a few of the other leafy spurge biocontrol agents. The long-horned
beetle (Oberea erythrocephala) and clear-winged moth (Chamaesphecia
spp.) are "stem-miners" that cause damage in two ways: Adults lay eggs
in stems, then the larvae hatch and burrow down the stem – weakening the
stem and stressing the plant – and into the root crown, where they feed and
cause additional damage. Oberea could potentially be important in
moist, sandy soils where flea beetles don’t work well. The gall midge (Spurgia
esula) is a tiny gnat that lays its eggs in leafy spurge flowers, which
produces a gall that prevents seed production. While these agents have
generally not produced significant spurge control, their long-term impact is
not yet known. It’s possible that some might play important roles in certain
situations or when used in combination with other agents. In addition,
researchers are always looking for new biocontrol agents, particularly
insects that can fill niches or habitats not occupied by agents that are
currently available.
Q: Where do I get flea beetles?
A: This is a very common question. It’s always best to start looking
locally. Flea beetles obtained from local sources won’t have to be stored
and transported far, and are more likely to be adapted to local conditions.
If you are unable to locate local sources through your county Extension
agent or weed officer, contact your state department of agriculture or
nearest USDA-APHIS PPQ office.
Q: Will harvesting flea beetles
this year reduce next year’s population, and will it retard leafy spurge
repression?
A: No, and no. There are always plenty of unharvested beetles, and
normal population development will continue even with extensive collection
efforts. Likewise, harvesting your flea beetles will not impact the
population’s ability to repress or control leafy spurge.
Q: Can flea beetles withstand long,
harsh winters?
A: Flea beetles have proven they can survive the long, harsh winters
common in the northern Great Plains by establishing populations and
controlling leafy spurge. There is some speculation, however, that a lack of
snow cover to provide insulation, combined with extended periods of
extremely cold weather, can adversely impact flea beetle populations.
Additional research into the topic is needed.
Q: How large of a patch of spurge is needed
for flea beetles?
A: This is a common, but
difficult to answer, question. Flea beetles can establish populations on
small patches of spurge (a half-acre or less), but may eliminate such
patches and be unable to maintain a population. Generally speaking, a
moderate to dense patch of spurge, a half-acre or more in size, is needed to
establish AND maintain a population. On a related topic, scattered patches
are OK but scattered plants aren’t – flea beetles cannot establish or
sustain a population on scattered plants.
Q: Can I spray over flea beetles with
herbicides?
A: As mentioned in the
Biological Control Manual, herbicides and flea beetles can indeed be
used together. The key is timing: Fall and early spring applications can
enhance population establishment by reducing densities and opening the
spurge canopy. However, late spring or summer applications will remove the
spurge top growth flea beetles need to complete their life cycle, and should
thus be avoided in situations where you are attempting to start or maintain
a population.
Q: Can I spray over flea beetles with
insecticides?
A: Flea beetles are
obviously susceptible to insecticides. In some situations, however – a
severe grasshopper outbreak, for example – the use of insecticides cannot be
avoided. If the use of insecticides at an established flea beetle site is
unavoidable, leaving small areas untreated can provide "reservoirs" of flea
beetles that will help sustain populations.
Grazing
Q: Where can I find good quality sheep to
graze leafy spurge?
A: There are a number of
quality livestock auctions in the northern Great Plains that handle large
runs of high quality breeding stock. Ranchers interested in grazing sheep as
a leafy spurge management tool, however, will likely need to do some
planning. For example, it’s much easier to buy sheep in the fall and
over-winter them instead of trying to find and buy sheep in the spring. One
option is to buy ewe lambs in the fall, over-winter them, graze them on
spurge the first year then start a breeding program. County extension agents
can sometimes provide information on local sources of sheep, and in some
cases, may know of sheep that are already trained. In addition, each state
in the northern Great Plains has an Extension sheep specialist who will be
able to provide advice and information on your particular state.
Q: Can you use mature sheep that are intended
for the kill market?
A: Absolutely. Studies show
that sheep gain a lot of weight during a season of grazing leafy spurge. In
fact, leafy spurge is high in crude protein, is easily digested and provides
especially good forage for lactating ewes and lambs.
Q: Will grazing leafy spurge impact normal
sheep functions such as growth, breeding, etc.?
A: No it will not. In fact,
sheep grazing leafy spurge will actually outperform sheep grazing native
range. This is simply due to the high quality of forage that leafy spurge
exhibits.
Q: Do I have to completely re-fence my
operation, and do I have to use woven wire?
A: Research studies have found that adding one to two extra wires on a
pre-existing 3- to 4- strand barb wire fence will work. It is recommended to
use a 5- to 6- strand barb wire fence to successfully keep sheep in. A four
to six strand electric fence will also work well. Woven wire is not really
needed. It is also recommended that the perimeter fences be the most
substantial in your management plan.
Q: How much of a diet overlap would one
expect to see between cattle and sheep, and what stocking rate is
recommended?
A: Dietary overlap of
cattle and sheep can be high or low depending upon biodiversity, forage
diversity and availability, environmental conditions, and management. The
dietary overlap can range from 30% to 70%, however, when grazing cattle and
sheep on leafy spurge infested rangeland the dietary overlap has the
potential of being low until a significant reduction in leafy spurge occurs.
Once this happens, individuals need to consider reducing the number of sheep
in order to reduce the competition for desirable, available forage for
cattle, yet still be effective in controlling leafy spurge.
Proper stocking rates are essential in gaining
control of leafy spurge. It has been found that an average of one to two
sheep per acre of leafy spurge for a four-month grazing season is required
to maintain acceptable control.
Q: Do you need to train naive sheep to
consume leafy spurge before releasing them out to pasture?
A: There is some debate on
this subject. Many people believe that sheep need to be trained to eat leafy
spurge. Research studies have used naive sheep and experienced sheep. From
these studies it was concluded that it largely depends on the diversity of
the plant community and sometimes the breed of sheep. It has been observed
that when a plant community is diverse in broadleaf plants, which are
preferred by sheep, there usually is a delay in the sheep selecting out
leafy spurge. After this period they develop an acquired taste for leafy
spurge and will readily consume it.
Q: What can one expect to see in the control
of leafy spurge using sheep? (example: first grazing season, second, etc.)
A: Depending on the type of
grazing treatment and stocking rate used, you will typically see an increase
in leafy spurge densities after the first year. This is not a bad thing.
What this is saying is that you have put stress on the plant. The increase
in leafy spurge densities is from the adventitious root system, triggered by
the grazing to put up more shoots. After the second and third year a
reduction should be noticeable. Depending on the management and growing
seasons 75 to 85 percent reduction can be expect by years five and six.
Q: When should I begin grazing sheep on leafy
spurge?
A: Sheep should begin
grazing leafy spurge as soon as it reaches 3 to 4 inches in height,
typically around the 15th of May. This growth is a key component in the
control of leafy spurge. By turning them out when the plant is 3 to 4 inches
tall, it will allow the sheep to prevent the majority of the leafy spurge
plants from going to seed.
Q: What do you use for predator control?
A: There are many
techniques that are beneficial. Using dry mature ewes with cow/calf pairs
has reduced losses; however, the most common methods of control used today
are donkeys, dogs, llamas, and the use of the local USDA Plant and Animal
Control division (Government Hunter and Trapper).
Q: When using a rotational grazing system
should I run the sheep together with the cattle or should I graze them ahead
of the cattle?
A: Sheep can be run with
the cattle, however, there are some precautions that should be used.
Producers that creep feed their calves may want to run the sheep ahead or
behind the cattle in the rotation to prevent the sheep from consuming their
desired creep feed. Also sheep are sensitive to copper. This may cause a
problem in areas were copper is deficient and producers use higher copper
content to supplement their cattle. Thus it would be more appropriate to run
sheep and cattle independent of each other.
Q: What would happen if I grazed the sheep
for three to four years and removed them, would the leafy spurge come back?
A: The answer is yes.
Within two to three years the leafy spurge will be back to the original
density without implementing any other control method. The use of sheep in a
long-term management plan is essential. Although you might not see any leafy
spurge you still have a viable seed bank and viable adventitious roots.
If you have additional questions or don’t see
your question listed here, please visit our
feedback
page and fill out the form or email us with your question. We'll do our
best to get back to you with an answer to your question.
Herbicides
Q: How far into the fall (according to the
temperature) can you spray leafy spurge and have good results?
A: The best timing varies by
herbicide. Plateau should be applied in mid-September for best results as
control may drop 50 percent or more if Plateau is applied in August or
October. Tordon plus 2,4-D has a wider application window and can be applied
from late-August to early September. Paramount has provided good leafy
spurge control even when applied in late October following several hard
frosts. Leaf color can vary from green to yellow and red. The key is to make
sure the leafy spurge leaves are still firmly attached to the stem so the
herbicide can be translocated to the roots. If leaf drop has begun, it is
best to wait until the following growing season before applying herbicides
for leafy spurge control.
Q: Can I spray over an area that has
biocontrol agents?
A: Yes, as long as the
herbicide is applied in the fall after the adults have finished egg laying.
Avoid herbicide application in June and July when the adults are feeding on
leafy spurge. No herbicide used for leafy spurge control directly affects
Aphthona spp. adults or larvae.
Q: How much water do I use?
A: Proper calibration of the
sprayer and uniform coverage is much more important than spray volume.
Typically, applicators using multi-nozzle spray booms apply herbicides at 10
to 20 gallons per acre. Herbicides applied with a single-nozzle back-pack
sprayer typically use 60 gallons or more per acre.
Q: When is the best time to spray?
A: Proper timing depends on
the herbicide you are using. See the text and flea beetle life cycle chart
on page 8.
Q: How long before cattle and sheep are
allowed to graze after a chemical application?
A: Tordon and Banvel can be applied even if the pasture has grazing
cattle present. However, do not transfer the livestock from treated areas to
pastures or cropland with sensitive broadleaf plants for at least 12 months
without first allowing seven days of grazing on an untreated grass pasture.
Otherwise urine may contain enough herbicide to cause injury to sensitive
plants. The waiting period after treatment with Banvel varies from seven to
90 days, so consult the label before using.
Q: How many applications of chemical are
recommended if used as an IPM method?
A: The number of
applications will vary depending on the success of the other control method
used in the IPM program. When used with Aphthona spp. flea beetles,
excellent control has been achieved with as few as one application, but
sometimes two to three annual applications are needed. If used in
conjunction with grazing animals, three annual treatments worked best.
Q: How close can I spray to water?
A: Long residual herbicides
such as Tordon and Banvel should not be used within 50 feet or less of a
body of water, depending on the terrain. Other leafy spurge herbicides can
be used near or in water. See pages 18-19, which describe specific
herbicides to control leafy spurge near water.
Q: What size of a leafy spurge patch generally
is too big for chemical treatments?
A: This is really dependent
on budget (see pages 26-27). Herbicides should be applied around the
perimeter of even very large infestations to prevent spread. It is never too
early to begin a treatment program, but it can be very costly to start years
after the program should have begun.
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