Recently
I’ve started seeing the Richardson ground squirrels start popping out of their
burrows, a reminder that it’s time to begin their control. The Richardson ground squirrel, which is commonly
referred to as a ‘gopher,’ is a medium sized ground squirrel with yellow-tan to
gray coloring and typically weighs 11 to 18 ounces. The Richardson ground squirrel predominately
lives east of the Continental Divide of Montana and causes extensive damage in
croplands, pastures, and hay fields. Research
has shown hay yields in alfalfa fields infested with ground squirrels have
shown a 24% reduction. Today, we’ll cover
a bit on the biology on the ground squirrel, and then cover management next
week. By understanding the ground
squirrel’s biology, we can better manage these pests.
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| Richardson ground squirrels can have up to 14 young per litter! By controlling the adults now, there will be far less to control in May and June when the young emerge as well. Photo by Kari Lewis. |
Ground
squirrels emerge from hibernation between February and April, depending on local
weather conditions and elevation. The first
ground squirrels to emerge from hibernation are the males. The males establish their breeding territories
in preparation for the females that emerge from hibernation 10 days to two weeks
after the males emerge. Once the females
emerge from hibernation, again, right about now, there is a short breeding
season and then after a three to four-week gestation period, the females give
birth to a single litter in April or May.
Ground squirrels reproduce quite prolifically. Typically, litters average six to seven
ground squirrels per litter, but could have as many as 14 per litter.
When
the ground squirrel young are approximately five weeks of age, they emerge from
the burrow and begin feeding on grass, crops, etc. So, if we assume that the adult males emerged
from hibernation March 15, that would put the females emerging approximately
March 25. After a short breeding season
and an approximate four-week gestation period, they would likely have their
litter in early May and by the end of May, their 2 to 14 ground squirrel young
have joined them in feeding on crops, rangeland, etc.
This
biology lesson of the ground squirrel helps illustrate why it is so critical to
provide early management control. By controlling
now, in March and April, there are only the adult males and females to
control. By waiting until May or June to
provide control (when the ground squirrel damage is clearly visible), there will
be a much, much larger population of ground squirrels to control.
For managing ground squirrels in
large areas, such as on rangeland or cropland, toxicants are commonly
used. Toxicants are poisonous items that
are designed to kill the animals that eat them.
Zinc phosphide and diphacinone are two toxicants registered for the
control of Richardson’s ground squirrels.
Zinc phosphide bait is most
effective when applied early in the spring, shortly after ground squirrels
emerge from hibernation, and before spring green-up. Zinc phosphide should not be applied if
moisture is forecasted within two days of application. Zinc phosphide may be applied by hand baiting
or broadcast baiting. Broadcast baiting
may be used in rangelands, pastures, non-crop areas, orchards and crop areas
including barley, wheat and alfalfa.
Ramik Green is an example of an
anticoagulant which is a general use pesticide.
Ramik green must be placed in rat-sized tamper-resistant bait
stations. Stations must be maintained
regularly to ensure a constant supply of bait for at least 30 days.
In large acreages, the use of toxic
grain bait may be the most cost-effective control method. Bait should be applied when the entire
squirrel population is active and readily accepting grain. The breeding period, which is going on now,
is the ideal time to control ground squirrels.
By controlling now, we can eliminate both adults and potential young as
well, to help minimize crop damage. If
we wait to control ground squirrels, vegetation begins to green-up and the
ground squirrels’ acceptance of grain bait is reduced.
If using a restricted use product,
applicators must have a private pesticide applicator’s license prior to
purchasing a restricted use product.
Licenses can be obtained through taking the test at your local extension
office or attending an upcoming class, such as the one April 25 in Great Falls. If you have any questions on receiving your
private pesticide applicators license, please call your local extension office.
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