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How to Manage Pests
UC Pest Management Guidelines
Sugarbeet
Spider Mites
Scientific names:
Twospotted spider mite: Tetranychus urticae
Carmine spider mite: Tetranychus cinnabarinus
(Reviewed 11/05,
updated 11/05)
In this Guideline:
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Spider mites resemble tiny spiders, no larger than a pin head.
Nearly identical in appearance, the carmine
mite occurs
on sugarbeets primarily in the Imperial Valley and the twospotted spider
mite is more common in other beet-growing areas of California. When newly hatched,
spider mites have three pairs of legs but as they mature, they develop four
pairs. They vary in color from nearly transparent to yellowish, greenish, or
even red. They have two darkly pigmented spots, one on each side of the body.
While visible to the unaided eye, they are best seen and identified with the
use of a 10X hand lens. Both species cause similar damage and are managed in
the same manner.
Mites feed on the undersurface of the leaf. They puncture cells on
the leaf surface and feed on the sap from leaves, leaving them blotched with
white or pale yellow spots, which range in size from mere specks to larger
areas as the specks coalesce. The damage is visible on both the upper and lower
surface of the leaf. Spider mites spin very
fine webs over the surface that become prominent as the number of mites per leaf
increases. Severe infestation can cause defoliation.
Spider mites are usually controlled by predatory insects and mites.
Outbreaks are often the result of plant stress or dusty conditions. Mature
sugarbeets can tolerate dozens to hundreds of mites per leaf without
significant reductions in yield or quality. Treatments may be necessary on
early and mid-season sugarbeets although treatment thresholds have not been
established.
Biological Control
Spider mites have numerous predators including lacewings, assassin bugs, damsel
bugs, minute pirate bugs, bigeyed bugs, and sixspotted thrips. Predatory
mites are
often found attacking spider mites. Predatory mites can be distinguished from
spider mites by their slightly larger size and a more flattened, pear-shaped
appearance. Predatory mites are clear, lacking any spots or coloration. These
natural enemies can keep spider mite populations in check and may bring spider
mites under control. Always check for their presence when you find mites in
your fields.
Cultural Control
Mites are more serious on stressed plants, particularly water-stressed
or dust-covered plants. Outbreaks may occur as a result of foliar applications
of organophosphates, carbamates, and pyrethroids used to control other pests
such as armyworms. Avoid using these insecticides where possible and observe
good cultural practices including adequate nutrition and irrigation.
Monitoring and Treatment Decisions
There are no economic thresholds for spider mites. If numbers continue
to increase in spite of the presence of biological control agents and injury
becomes severe, treatments might be necessary.
| Common name |
Amount/Acre |
P.H.I.+ |
| (trade name) |
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(days) |
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| When choosing a pesticide, consider information relating
to water quality and impact on natural enemies and bees Not all registered pesticides are listed. Always read label of product being used.
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| A. |
NALED* |
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(Dibrom 8) |
1 pt |
2 |
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MODE OF ACTION: An organophosphate (Group 1B)1
miticide.
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COMMENTS: May give good initial control, but resurgence (primarily from hatching eggs) can be a serious problem. |
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| B. |
SULFUR DUST# |
35-40 lb |
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MODE OF ACTION: An inorganic (unknown mode of action)1
miticide.
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| C. |
MICRONIZED SULFUR# |
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(Microthiol Disperss) |
5-10 lb |
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MODE OF ACTION: An inorganic (unknown mode of action)1
miticide.
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UC IPM Pest Management Guidelines: Sugarbeet
UC ANR Publication 3469
Insects and Mites
C. G. Summers, Entomology,
Kearney Agricultural Center, Parlier
D. R. Haviland, UC IPM Program, Kern Co.
L. D. Godfrey, Entomology, UC Davis
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