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How to Manage Pests
UC Pest Management Guidelines
Pear
Lygus Bugs
Scientific names:
Western tarnish plant bug: Lygus hesperus
Pale legume bug: Lygus elisus
(Reviewed 2/07,
updated 3/8)
In this Guideline:
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Lygus bug damage may occur in all major pear districts but is mostly
a pest in Delta area pear orchards. Lygus attack is more frequent in orchards
having permanent cover crops and in orchards adjacent to crops or vegetation
that host lygus. Lygus bugs vary in color from pale green to yellowish brown
with reddish brown to black markings, but can be distinguished by a prominent
triangle in the center of the back. The lygus bug adult is about 0.25 inch (6
mm) long and 0.1 inch (2.5 mm) wide, flattened on the back. Nymphs resemble
adults, but are smaller and do not have wings. Five black spots are
visible on the back on later nymphal instars.
Lygus bugs may feed on developing flower buds early in spring,
causing the buds to exude gum and shrivel up. Usually this damage is not
serious unless a very heavy infestation is present. Lygus cause their most
serious damage by feeding directly on fruit. Mid-season feeding results in round pits, and late
season feeding causes irregularly shaped depressions that are similar to stink bug damage.
Peel the fruit and examine the feeding site to distinguish the two types of
damage. The area where lygus feeds develops an open pustule. If the flesh of the fruit is examined
beneath the pustule, hard cells clustered into a core can be seen. Feeding by stink bugs creates
a depression in the fruit with white, pithy areas underneath the skin.
In Delta area pear orchards, the potential for a lygus bug population
to cause damage is difficult to assess. Lygus bugs may be present in
substantial numbers in the orchard and cause no damage; however, they can often
cause damage and may attack fruit at any time from petal fall to harvest.
Annual preventive treatments are costly and subject to failure because lygus
bugs have been quick to develop resistance to chemicals. Use monitoring
guidelines to make treatment decisions. In orchards with a history of lygus
damage, monitor fruit at least every 2 weeks between petalfall and
harvest to assess the need for treatment.
Biological
Control
The role of predators and parasites in controlling
lygus in orchards has not been investigated.
Cultural
Control
Reduce or suppress weed host plants before fruit
forms and thereafter throughout the growing season to minimize lygus
populations. Yellow starthistle, sweet clover, wild mustard,
and vetch are important hosts. Do not allow cover crops to dry out or to grow
excessively between mowings. Orchards located near alfalfa fields are at a
unique risk and infestations may coincide with cuttings.
Organically
Acceptable Methods
Cultural control is an organically acceptable
method.
Monitoring
and Treatment Decisions
If an orchard has had a history of lygus injury,
take fruit samples at least every 2 weeks starting soon after petal fall and
continue until harvest. After fruit has formed, sample the cover crop and weeds
with a sweep net to determine if lygus bugs are present in the orchard. Lygus
bugs may be present in the orchard but not feeding on the fruit, so you need to
check the fruit for damage.
Examine the fruit in 40 clusters (see SAMPLING DURING FRUIT DEVELOPMENT for
more information). Because lygus damage is often spotty in distribution, check
each 20-acre block thoroughly. Lygus may migrate into the orchard at any time
during the growing season and damage frequently appears first along orchard
borders. One damaged pear in 100 is cause for concern and calls for further
sampling and evaluation of control need. When sampling fruit for other pests,
also look for the presence of lygus bugs on fruit or in the trees to determine
if they are still present in the orchard. Because the bugs move quickly and may
be difficult to see, the number seen will depend on the skill of the observer.
When lygus are migrating into an orchard, periodic spraying of borders will
hold down numbers and reduce damage.
Harvest
fruit sample. At harvest, assess your IPM program by monitoring
fruit in bins for lygus bug damage. Sample 200 fruit from 5 bins per orchard
(or 20-acre block in large orchards) for a total of 1,000 fruit. For
information on monitoring other pests at this time, see HARVEST FRUIT SAMPLE.
| Common name |
Amount to Use** |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
(conc.) |
(dilute) |
(hours) |
(days) |
|
| The
following materials are listed in order of usefulness in an IPM program,
taking into account efficacy and impact
on natural enemies and honey bees. When choosing a pesticide,
also consider information relating to environmental impact.
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| A. |
FENPROPATHRIN* |
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(Danitol) 2.4EC |
16–21.33 fl oz |
4–5.3325 fl. oz. |
24 |
14 |
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MODE
OF ACTION GROUP NUMBER1: 3
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COMMENTS: Harmful to beneficial insects and mites; will suppress spider mites. |
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| B. |
LAMBDA-CYHALOTHRIN* |
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(Warrior with Zeon) |
2.56-5.12 fl oz |
— |
24 |
21 |
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MODE
OF ACTION GROUP NUMBER1: 3
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COMMENTS:
Do not apply more than 0.2 lb a.i. 1.6 pt/acre/year. Do not apply more than
0.16 lb a.i. (1.28 pt product)/acre/year post bloom. Harmful to beneficial
insects and mites; will suppress spider mites. May cause outbreaks of pear rust mite. |
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| C. |
THIAMETHOXAM |
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(Actara) |
4.5-5.5 oz |
1.125-1.375 oz |
12 |
see comments |
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MODE
OF ACTION GROUP NUMBER1: 4A
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COMMENTS:
Allow a minimum of 10 days between applications; do not exceed 8
oz/acre/season. Preharvest interval is 14 days when 2.75 oz/acre or less is used and 35 days when more than 2.75 oz/acre is used. |
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| D. |
IMIDACLOPRID |
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(Provado) 1.6 F |
10 fl oz |
2.5 fl. oz |
12 |
7 |
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MODE
OF ACTION GROUP NUMBER1: 4A
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COMMENTS: Effective against boxelder and lygus bugs, but not stink bugs. |
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| E. |
DIMETHOATE |
Label rates |
48 |
28 |
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MODE
OF ACTION GROUP NUMBER1: 1B
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COMMENTS: May kill beneficial mites and pear psylla predators. |
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| F. |
FORMETANATE HYDROCHLORIDE |
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(Carzol) SP |
1 lb |
4 oz |
see comments |
0 |
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MODE
OF ACTION GROUP NUMBER1: 1A
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COMMENTS:
Most disruptive to beneficial mites and psylla predators. Do not apply after
petalfall. See label for second application restrictions. Restricted entry
interval (R.E.I.) is 4 days if during the dormant season, 10 days for hand labor activities, and 16 days for harvest. |
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UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension Sonoma Co.
R. B. Elkins, UC Cooperative Extension Lake Co.
R. A. Van Steenwyk, Insect Biology, UC Berkeley
C. Ingels, UC Cooperative Extension Sacramento Co.
Acknowledgment for contributions to the insects and mites section:
C. Pickel, UC IPM Program, UC Cooperative Extension Sutter/Yuba counties
P. W. Weddle, Weddle, Hansen & Associates
P. Chevalier, United Ag Products, Ukiah; B. Knispel, United Ag Products, Kelseyville
T. Lidyoff, Purity Products, Healdsburg; G. McCosker, AgroTech, Kelseyville
B. Oldham, Ag Unlimited, Ukiah
D. Smith, Western Farm Service, Walnut Grove
J. Sisevich, AgroTech, Kelseyville
B. Zoller, The Pear Doctor, Inc., Kelseyville
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