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How to Manage Pests
UC Pest Management Guidelines
Plum
San Jose Scale
Scientific name: Diaspidiotus (Quadraspidiotus) perniciosus
(Reviewed 5/06,
updated 5/06)
In this Guideline:
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DESCRIPTION OF THE PEST
San Jose scale, a
major pest of fruit trees, is inconspicuous and usually not noticed until it
builds up to large numbers on limbs. Limbs supporting large populations often
ooze gum and exhibit rough bark and
dieback. Dead leaves adhering to fruit spurs during dormant season indicate the
presence of scale. Partially mature nymphs overwinter on limbs and trunks. In
spring the nymphs develop into winged
male and sessile female scale insects. Female scales have gray circular scale coverings. If the covering is removed, the lemon
yellow body beneath can be seen. In May females lay eggs that hatch immediately and the young
emerge from under the edge of the adult scale cover. The young crawlers settle on shoots where they feed and become adults or overwinter as partially
grown scales. In California there are five overlapping generations each year.
Crawlers first appear in late April and May, followed by continuous overlapping
emergence from late June through December.
DAMAGE
San Jose scale can infest branches, shoots, leaves, and fruit.
Adults and nymphs suck plant juices and cause considerable damage. They have
been known to seriously weaken branches and main scaffold limbs, thus causing
permanent injury to mature trees. Crawlers settling on fruit may cause fruit spotting.
MANAGEMENT
San Jose scale has many natural enemies that can frequently keep the
pest under control if not disrupted by application of broad-spectrum
insecticides. Many orchards that have not used broad-spectrum sprays for 2 or 3
years do not have San Jose scale problems. The best time to spray is during the
dormant season when low-to-moderate populations can be managed with oil sprays,
which don't destroy the scale parasites. The scale is monitored as part of the
shoot sample during the dormant season and with pheromone traps in spring.
Biological Control (View
photos of healthy and parasitized San Jose scale.)
Natural enemies that feed on San Jose scale include two predaceous
beetles: the twicestabbed lady beetle, Chilocorus
orbus, and another small beetle Cybocephalus
californicus. A number of small chalcid and aphelinid wasps, including Aphytis and Encarsia
(Prospaltella) sp., parasitize this scale. These predators and parasites are helpful in reducing
scale populations, but broad-spectrum insecticides used during the growing
season for other pests disrupt this natural control, and scale populations can
build as a result. Low winter mortality due to mild temperatures will also
permit a buildup of scale populations.
Organically Acceptable Methods
Oil sprays and biological control by native scale parasites are acceptable in organically
managed orchards.
Monitoring and Treatment
Decisions Degree-day calculator Degree-day table
Dormant season. Monitor San Jose scale during the dormant season by
collecting 100 spurs and examining them for live scale as well as for tiny
emergence holes, which indicate parasite activity. For details on sampling, see
DORMANT SPUR SAMPLING and the monitoring
form .
There is a correlation between infested spurs and infested plums,
however, plums harvested in mid-June don't generally need a treatment. Expect
more damage in late-harvested plums and treat them with oil at greenbud or
popcorn if 3 spurs out of 100 are infested. If over 10% are infested, add an
insect growth regulator (pyriproxyfen) to the oil sprays. Follow the guidelines below:
Dormant Treatment Decision Table (% infested spurs)
| Treatment threshold |
Treatment |
| Harvested before June 15 |
Harvested after June 15 |
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| Below 20% |
Below 5% |
No treatment |
| 20-60% |
5-10% |
Oil at 6 gal/acre |
| Over 60% |
Over 10% |
Oil at 6 gal/acre plus insect growth regulator1
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Oil alone can be effective in controlling low-to-moderate
populations (apply before January 21). If populations are high, include an
insect growth regulator (pyriproxyfen-Esteem, Seize) with the oil.
Organophosphates are available but are associated with environmental problems
and should be avoided. When the dormant organophosphate and oil spray is first
omitted, San Jose scale populations may increase the first year but by the
second and third year parasite populations have increased to levels where they
reduce San Jose scale populations and maintain them at low levels. If you
notice parasitized scale in your dormant sample, be sure to only use an insect
growth regulator during the growing season.
Growing season. Monitoring with pheromone traps
during the growing season will help you keep track of the appearance and
development of scale populations as well as the level of parasitism (Aphytis and Encarsia) but does not tell you if treatment is needed. It mainly tells you how to time treatment for best control in spring using
degree-days and pheromone traps to predict the crawler stage or sticky traps to
trap the crawlers. Need for treatment is better assessed during the dormant
season. Delayed dormant sprays are the preferred timing for treatment.
If inadequate control is achieved with the dormant spray or the
dormant spray is not applied, treatment is also effective when applied soon
after the emergence of crawlers in May. Monitor scales by putting up pheromone traps around February 25 (see PHEROMONE TRAPS) and placing sticky tape in the trees in April. Record results on a monitoring form. Place pheromone traps well within the canopy to keep them out of the wind. San Jose scale traps will
attract both male San Jose scales and scale parasites (Aphytis
melinus and Enarsia perniciosi). Adult male scales can be distinguished from the
parasites by the presence of a dark line across their thorax where the wings
attach.
When the traps begin to catch males consistently, start accumulating
degree-days using a 51°F lower threshold and a 90°F upper threshold. If it is
needed, apply a treatment for crawlers 600 to 700 DD after you catch the first
males. Be aware that the traps may fail to catch any adults if weather is cold,
rainy, or windy. Total generation time for San Jose scale is 1050 DD. (For
assistance in calculating degree-days, see "Degree-days".)
If May sprays are required, use a high-volume (dilute) application
at 400 gallons or more per acre for best coverage; do not use a low volume
application.
Take a fruit damage sample at harvest to assess the effectiveness
of the current year's IPM program and to determine needs of next year's
program. See FRUIT
EVALUATION AT HARVEST. Record results on a monitoring form .
| Common name |
Amount/Acre** |
P.H.I.+ |
| (trade name) |
(conc.) |
(dilute) |
(days) |
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| The following materials are listed in order of usefulness in an IPM program,
taking into account efficacy, impact on natural enemies and honey bees, and
impact of the timing on beneficials. When choosing a pesticide, also consider
information relating to environmental impact. |
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| DELAYED DORMANT |
| A. |
DORMANT OIL such as: |
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DORMANT FLOWABLE EMULSION |
6 gal |
1–1.5 gal |
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NARROW RANGE OIL# |
4 gal |
1.5 gal |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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COMMENTS: Cover all parts of the tree. Will
control low-to-moderate infestations. See Dormant Treatment Decision Table
for rate to use based on % infested spurs. Oil applications at this time may
cause some young shoots to burn or dieback, especially in years when trees
are water-stressed, or have recently been subjected to freezing temperatures
or to dry winds. Dormant flowable emulsion is less likely to cause burn. Some
varieties, especially those that are weak growers or low in vigor because of
soil or other location-related issues, can be especially sensitive to oil.
Not all oil products are organically acceptable; be sure to check individual products. |
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| B. |
DORMANT OIL such as: |
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DORMANT FLOWABLE EMULSION |
6 gal |
1–1.5 gal |
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NARROW RANGE OIL |
4 gal |
1.5 gal |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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COMMENTS: Cover all parts of the tree. Use
with an insecticide for high infestations. Oil applications at this time may
cause some young shoots to burn or dieback, especially in years when trees
are water-stressed, or have recently been subjected to freezing temperatures
or to dry winds. Do not use oil sprays on water-stressed trees. Dormant
flowable emulsion is less likely to cause burn. Some varieties, especially
those that are weak growers or low in vigor because of soil or other location-related issues, can be especially sensitive to oil. |
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. . . PLUS. . . |
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PYRIPROXYFEN |
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(Esteem) 0.86 EC |
13–16 fl oz/acre |
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(Seize) 35WP |
4–5 oz/acre |
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MODE OF
ACTION: An insect growth regulator (Group 7C)1 insecticide.
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COMMENTS: An insect growth regulator. Do
not apply more than once per growing season. Good coverage is essential for
good control. Preferred treatment of high populations of scale in an environmentally sound program. Use allowed under a supplemental label. |
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. . . OR. . . |
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DIAZINON* 50WP |
4 lb |
1 lb |
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MODE OF ACTION: An organophosphate (Group
1B)1 insecticide.
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COMMENTS: Resistance may be found in areas
of the southern and south central San Joaquin Valley. Avoid drift and runoff
into surface waters or choose alternative materials. Diazinon has been found
in surface waters at levels that violate federal and state water quality standards. |
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. . . OR. . . |
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CHLORPYRIFOS* |
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(Lorsban) 4E |
2 qt |
1 pt |
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MODE OF ACTION: An organophosphate (Group
1B)1 insecticide.
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COMMENTS: Apply concentrate spray with a
minimum of 100 gal/acre. Do not apply in the following counties: Butte,
Colusa, Glenn, Solano, Sutter, Tehama, Yolo, and Yuba. Do not use more than 4
gal narrow range oil/acre with this material, apply more than once during
dormant season, or allow meat or dairy animals to graze in treated orchards.
Do not apply until winter rains or irrigation has replenished soil moisture.
Do not allow livestock to graze in treated orchards. Avoid drift and runoff
into surface waters or choose alternative materials. Chlorpyrifos has been
found in surface waters at levels that violate federal and state water quality standards. |
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| SPRING |
| A. |
PYRIPROXYFEN |
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(Esteem) 0.86 EC |
13–16 fl oz/acre |
14 |
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(Seize) 35WP |
4–5 oz/acre |
14 |
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MODE OF
ACTION: An insect growth regulator (Group 7C)1 insecticide.
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COMMENTS: Apply when scale crawlers first
emerge. Do not apply more than
once per growing season. Good coverage is essential for good control. Use allowed under a supplemental label. |
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| B. |
NARROW RANGE OIL# |
6–8 gal |
1.5–2 gal |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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COMMENTS: Use this option if bloom sprays
are used for control of caterpillars. Plum trees tolerate oil treatments
better in spring than during dormancy. Do not apply oil within 2 weeks of
captan or within 30 days of a sulfur treatment. Not all oil products are organically acceptable; be sure to check individual products. |
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| C. |
DIAZINON |
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50 WP |
3 lb |
1 lb |
21 |
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4 EC |
3 pt |
1 pt |
21 |
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MODE OF ACTION: An organophosphate (Group
1B)1 insecticide.
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COMMENTS: Resistance may be found in areas
of the southern and south central San Joaquin Valley. Avoid drift and runoff
into surface waters or choose alternative materials. Diazinon has been found
in surface waters at levels that violate federal and state water quality standards. Where plums are grown near waterways, do not use diazinon. |
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UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier
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