How to Manage Pests
UC Pest Management Guidelines
Pacific coast wireworm: Limonius canus
Sugarbeet wireworm: Limonius californicus
Dryland wireworm: Ctenicera pruinina
In this Guideline:
Wireworms are the soil-dwelling larvae of click beetles. Several
wireworm species occur in western potato soils, but the most common are the
Pacific coast wireworm, the sugarbeet wireworm, and the dryland wireworm.
Several species of the genus Conoderus have also been encountered in
some production areas.
Adult wireworms are slender, reddish brown to black click beetles that are 0.25 to
0.5 inch long. The larvae are
wirelike, having hard bodies that are slender, cylindrical, yellowish to brown
in color, and about 0.75 inch long when full grown. Common wireworm species
require 3 to 4 years to complete their life cycle. Most of the time is spent in
the larval stage, but all stages may be present at once during the growing
Adults do not damage potatoes, but the larvae, or wireworms, may
damage seed pieces and young root systems during stand establishment, resulting
in poor stands. More commonly the damage is seen as shallow to deep holes in
the potatoes, caused by wireworms burrowing into the tuber while feeding.
Wireworms bore perpendicularly or diagonally to depths up to 0.5 inch, but do
not tunnel all the way through the tuber.
The best time to manage
wireworms is before planting. Check for wireworms by observing the field during
plowing or discing, or by baiting. If wireworms are present, monitor by taking
soil samples to determine the need to treat.
In recent years,
wireworms have been most common in the northern mountain areas in fields that
have been in weedy alfalfa or pasture for several years before potatoes. Avoid
planting potatoes in fields immediately following clover, grass, pasture, or
weedy alfalfa. Summer fallow will reduce wireworm numbers by drying the soil.
Cultural controls are
acceptable to use on an organically certified crop.
Monitoring and Treatment
The most direct way to detect wireworms in a field is by general
observation during plowing or discing of a field, particularly where old
alfalfa, clover, or pasture is being taken out. Wireworms can also be detected
by baiting, using carrots, packets of untreated corn and/or wheat seed, or
ground whole wheat flour, provided they are used when soil temperatures are
50°F at 4 to 6 inches deep. Baiting does not give a good estimation of the
density of the population. If baiting shows the presence of wireworms, take
soil samples to estimate the wireworm density. Use a 6-inch post hole digger
and a shaker/sifter to sample. Take samples in spring when soil temperatures
are 45°F or higher at the 6-inch level or in late summer at the 18-inch level.
The following guide is used in some production areas.
|Acres in field
||Number of soil samples
||Treatment threshold (# of wireworms)
treatments have provided adequate control in limited field tests conducted in
California. Band treatments are used in some areas, but have not been evaluated
under California conditions. In areas where potatoes are planted in late fall
and winter, soil-applied insecticides tend to break down before wireworms
become active when the soil warms in spring.
|When choosing a
pesticide, consider information relating to the impact on natural enemies
and honey bees and
environmental impact Not all registered pesticides are listed. Always read label of product being used.
||MODE OF ACTION GROUP
||COMMENTS: Broadcast on
soil and thoroughly work into the soil to a depth of 6–9 inches before
planting. Soil temperature must be 50°F or higher when ethoprop is applied. May also be applied at planting or before crop emergence.
UC IPM Pest Management Guidelines: Potato
UC ANR Publication 3463
L. D. Godfrey, Entomology, UC Davis
D. R. Haviland, UC Cooperative Extension, Kern Co.
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