Agriculture Reference
In-Depth Information
Numerous species of wireworm attack po-
tato in different growing regions, and Jansson
and Seal (1994) noted at least
39
species of
wireworm attack potatoes. In most regions, two
or more species are generally considered to be
the primary pest wireworms of potato, but due
to complexity in sampling and the difficulty in
morphological identification, there is not always
a strong consensus as to the species involved.
Further complicating the matter, oftentimes
more than one pest species of wireworm can be
found in individual fields.
were effective, little research was conducted on
wireworm biology and control. In recent years,
however, many insecticides of those classes have
been banned from use, removed from the market-
place, or are significantly restricted. Wireworms
have resurged as a significant pest problem, result-
ing in more current studies on their biology and
control with newer insecticides.
Sampling and monitoring
With most of the life stages of the wireworm being
subterranean and the distribution of wireworms
in fields uneven, the development of economic
thresholds and accurate sampling for risk assess-
ment have been challenging. Wireworms can be
found throughout the soil profile, from the surface
down to depths greater than 1.5 m, and can move
easily and quickly within that profile, depending
on soil temperature and moisture, and life stage.
There are two general methods employed for sam-
pling of wireworm larvae, the absolute method
and the relative method. Both methods have
strengths and weaknesses.
The absolute sampling method aims to esti-
mate the size of the wireworm population and
its distribution within the field by removing and
inspecting different soil strata by excavation or
soil cores. With the absolute method, a large
number of samples or cores per field must be
evaluated in order to assess the risk of wireworm
damage. The samples are simply extracted and
screened or sorted by hand to detect the number
of larvae per unit area of soil.
The relative sampling method employs the
use of an attractant or bait in order to measure
the abundance of wireworm, and therefore the
risk of damage. Many different types of baits
have been used, but the primary cue that at-
tracts wireworm to the different baits is the
emission of CO
2
. In the field, decomposing plant
material, germinating seeds, and plants respir-
ing all emit CO
2
, and therefore attract pest in-
sects, including wireworm. The relative method
requires fewer samples per field, but does risk
overestimating populations, since the baits at-
tract wireworm from some distance. Addition-
ally, several factors may affect attractiveness to
bait and overall trap count numbers, including the
amount of CO
2
generated, feeding status or stage
of the wireworm, duration of the baiting period,
soil temperature, soil moisture, soil texture, and
Damage
Wireworms are unique pests because they are
not transient in nature; rather, they are
long-term residents of fields into which potatoes
are planted. Wireworm larvae damage potatoes
by feeding on roots, but more important eco-
nomic damage comes from feeding on tubers.
Larval feeding early in tuber development re-
sults in holes that grow in size and suberize as
the tubers grow, leading to misshapen tubers.
Larval feeding later in tuber development results
in small round holes. Single holes caused by
wireworm render fresh market tubers unmar-
ketable, while tubers that will be processed or
used as seed can incur a higher number of feed-
ing holes per tuber without significant economic
loss. Under some conditions, wireworm damage
may occur immediately prior to harvest, with
the insects still inside the tubers.
Crop history plays a critical role in pre-
dicting the risk of damage by wireworm. Most
wireworms have a broad host range, but prefer
undisturbed soils with grass hosts. As such, pro-
duction fields coming out of pasture or range-
land can be particularly active sites for wireworm.
Miles and Cohen (1938) noted that waiting to
plow pastures just prior to planting potato could
reduce damage as compared to plowing well in
advance of planting. It has been assumed that
in the above scenario, wireworm larvae feed on
the decomposing plant material rather than the
potato crop, but once the decomposing sod is
reduced, feeding on the potato crop will ensue.
Additionally, for many years following World
War II, wireworms were not a significant issue due
to the environmentally persistent insecticides,
such as organochlorines, organophosphates, and
carbamates, used to control them. Because they
