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How to Manage Pests
UC Pest Management Guidelines
Pear
Pear Scab
Pathogen: Venturia pirina
(Reviewed 2/07,
updated 3/8)
In this Guideline:
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Scab first appears as velvety, dark olive-to-black spots on fruit,
leaves, and stems. When infections occur early, fruit
spots become scablike with age and the fruit may become misshapen. On leaves,
infections cause leaf puckering and twisting and eventually tear with age. Secondary
infections that occur later in the season appear as black, velvety pinpoint spots on fruit
and leaves.
In California, the fungus overwinters in dead leaves on the ground.
Primary spores are discharged from flask-shaped fruiting bodies in infected
dead leaves during spring rains and infect young leaves and fruit during
periods of prolonged moisture. These infections produce secondary spores, which
may cause further spread of disease during wet periods. Overwintering twig
lesions from secondary infections may also be an important source of innoculum
in spring.
The main objective in scab management is the reduction or prevention
of primary infections in spring. Extensive primary infections result in poor
fruit set and make scab control during the season more difficult. If primary
infections are successfully controlled, secondary infections will not be
serious.
Applying high
rates (20 to 24 gal/acre) of lime sulfur in fall before leaf fall may help
suppress maturation of primary spores the following spring, but more research
is necessary to confirm this. Similar rates of lime sulfur applied in the
delayed dormant period can significantly reduce the viability of overwintering
twig lesions, which are usually only a significant source of disease inoculum
during severe scab outbreaks. Applying a 5% solution of biuret urea spray at 50
pounds per 100 gallons dilute spray before leaf fall hastens leaf decomposition
and may reduce spore production the following spring. Combining the two
practices of applying lime sulfur in fall and urea before leaf fall may offer
complementary control. Cultivating leaves into the soil, however, has not
significantly reduced infection potential.
Biological Control
No biological controls have been found.
Monitoring
Pear scab outbreaks can be predicted based on temperature and
moisture conditions. The table listed here, derived from research by Mills and
LaPlante, gives hours needed at various temperature levels under constantly wet
conditions for primary spores to cause infection. In recent years automated
weather stations have been programmed to provide this information. If wet
periods are intermittent, total their durations until there is a period of at
least 8 hours of continuous dryness. If the dry period is sunny and drying is
quick and thorough, it is assumed that 6 hours after the trees have dried the
danger is passed. If drying is slow and humidity remains high, then the 8-hour
dry period is extended by a safety margin of 3 to 4 hours.
Harvest fruit sample. At harvest, assess your IPM program by monitoring
fruit in the bins for pear scab damage.
Sample 200 fruit per bin from 5 bins per orchard (or 20-acre block in
large orchards). (For more information, see HARVEST FRUIT SAMPLE.)
Postharvest shoot sample. Following harvest, sample 20 top shoots for scab lesions
on the leaves. If lesions are found, make plans to treat in spring. (For more
information about sampling, see POSTHARVEST SURVEY and
DORMANT/DELAYED
DORMANT SAMPLING.)
Treatment Decisions
Preventive program. For areas of heavy
rainfall, treat rows every 7 to 10 days starting at green tip until primary spore release is complete (5 to 10 weeks). Thereafter, maintain
vigilance until hot, dry weather produces conditions unfavorable for infection.
Eradicant
program. For low rainfall areas, treat as
soon as possible after an infection period with a material that has kickback
control of established infections. See the table below ("Period of
Effectiveness") for a list of fungicides with kickback activity. Monitor
infection periods daily throughout the spring and use the Mills and La Plante
table to ensure coverage of newly exposed growth as long as rains are occurring
frequently. Where infections are severe, consider applying fall and/or delayed
dormant treatments of lime sulfur to reduce overwintering inoculum.
| Fungicide |
PERIOD OF EFFECTIVENESS1 |
| When used as protectant (days) |
When used as kickback2 (hours) |
| Copper |
7–10 |
— |
| Dithane |
6–7 (or until rained on) |
0 |
| Flint |
7–10 |
100 |
| Lime sulfur |
5–7 |
36 |
| Procure |
7–10 |
48–72 |
| Rubigan |
14 |
96 |
| Scala |
7 |
— |
| Sovran |
7–10 |
96 |
| Syllit |
5–7 |
36 |
| Topsin-M |
5–10 |
36–48 |
| Vangard |
7–10 |
03 |
| Wettable sulfur |
3–5 (or until rained on) |
0 |
| Ziram |
7 |
0 |
TABLE 1. Mills and La Plante Table:
Hours of Wetting Required for Primary Infection During Spring. (After infection is established and
secondary spores are present in large numbers, hours for reinfection are only two-thirds of figures shown.)
Average temperature (F) |
HOURS TO INFECT |
Days until lesions appear |
| Light infection |
Moderate infection |
Heavy infection |
| 33–41 |
over 48 |
— |
— |
— |
| 42 |
30 |
40 |
60 |
— |
| 43 |
25 |
34 |
51 |
— |
| 44 |
22 |
30 |
45 |
— |
| 45 |
20 |
27 |
41 |
— |
| 46 |
19 |
25 |
38 |
— |
| 47 |
17 |
23 |
35 |
— |
| 48 |
15 |
20 |
30 |
17 |
| 49 |
14.5 |
20 |
30 |
17 |
| 50 |
14 |
19 |
29 |
16 |
| 51 |
13 |
18 |
27 |
16 |
| 52 |
12 |
18 |
26 |
15 |
| 53 |
12 |
17 |
25 |
15 |
| 54 |
11.5 |
16 |
24 |
14 |
| 55 |
11 |
16 |
24 |
14 |
| 56 |
11 |
15 |
22 |
13 |
| 57 |
10 |
14 |
22 |
13 |
| 58 |
10 |
14 |
21 |
12 |
| 59 |
10 |
13 |
21 |
12 |
| 60 |
9.5 |
13 |
20 |
11 |
| 61 |
9 |
13 |
20 |
10 |
| 62 |
9 |
12 |
19 |
10 |
| 63 |
9 |
12 |
18 |
9 |
| 64 |
9 |
12 |
18 |
9 |
| 65 |
9 |
12 |
18 |
9 |
| 66–75 |
9 |
12 |
18 |
8 |
| 76 |
9.5 |
12 |
19 |
9 |
| 77 |
11 |
14 |
21 |
9 |
| 78 |
13 |
17 |
26 |
10 |
| Common name |
Amount to use** |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
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| The following materials are listed in order of
usefulness in an IPM program, taking into account efficacy.
When choosing a pesticide, also consider information relating to
environmental quality.
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| DELAYED DORMANT |
| A. |
LIME SULFUR# |
6 gal/acre |
48 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) |
| |
COMMENTS: Highly effective at killing twig lesions; apply lime
sulfur at this time if twig lesions are present. Apply in 400 gal/acre. Lime
sulfur is incompatible with most other pesticides. Check before use. Do not combine with oil or use on Comice. |
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| GREEN TIP THROUGH SPRING
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| A. |
FENARIMOL |
| |
(Rubigan) EC |
9–12 oz/acre |
12 |
30 |
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MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) |
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COMMENTS: Follow label directions carefully. Use only before white bud and after full bloom. Has protectant and eradicant action. |
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| B. |
TRIFLUMIZOLE |
| |
(Procure) 50WS |
8–16 oz/acre |
12 |
14 |
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MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) |
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COMMENTS: Use only before white bud and after full bloom. Has protectant and eradicant action. |
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| C. |
TRIFLOXYSTROBIN |
| |
(Flint) |
2–2.5 oz/acre |
12 |
14 |
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MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: Do not apply more than 2 consecutive applications before alternating with a fungicide that has a different mode of action. |
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| D. |
CYPRODINIL |
| |
(Vangard) WG |
3 oz/acre |
12 |
72 |
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MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) |
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COMMENTS: Apply as a tank mix only with fungicides of a
different chemistry. Do not apply cyprodinil by itself to pears. This
material is more effective when temperatures are below 80°F. Do not apply more than 22 oz/acre/year. |
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| E. |
KRESOXIM METHYL |
| |
(Sovran) |
3.2–6.4 oz/acre |
12 |
30 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: Begin applications at 1/2 inch green or when
conditions are conducive to disease development. Repeat at 7- to 10-day intervals. Do not apply more than 25.6 oz/acre/season. |
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| F. |
PYRIMETHANIL |
| |
(Scala) SC |
7–10 fl oz/acre |
12 |
72 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) |
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COMMENTS: Make application on 7-day interval or longer, depending
on disease conditions. Do not apply more than 40 fl oz product/acre/crop. |
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| G. |
THIOPHANATE METHYL |
| |
(Topsin-M) |
0.25 lb/100 gal water |
72 |
1 |
| |
MODE OF ACTION
GROUP NAME (NUMBER1): Methyl benzimidazole (1)
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COMMENTS: Apply at 5- to 10-day intervals from green tip
through petal fall; continue at 7-to 14 day intervals as needed. Do not apply more than 4 lb product/acre/season. |
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| H. |
MANCOZEB |
| |
(Dithane DF, Penncozeb) |
3–6 lb/acre |
24 |
77 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3) |
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COMMENTS: Apply according to label instructions. This material
is used when russeting is a concern. The high rate is necessary for good scab and russet control. An important material in a resistance management program. |
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| I. |
DODINE |
| |
(Syllit) FL |
3–4.5 pt/acre |
48 |
14 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M7) |
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COMMENTS: Use 4.5 pt/acre in the first application and 3 to
4.5 pt/acre in subsequent sprays as needed. Apply at 5- to 7-day intervals or
as needed. Do not make more than 6 applications per season. A maximum of two
applications may be made in the final two months before harvest: one made no
later than 14 days before harvest and the final application no later than 7 days before harvest. |
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| J. |
LIME SULFUR# |
2 gal/100 gal water |
48 |
0 |
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. . . PLUS . . . |
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WETTABLE SULFUR# |
4 lb/100 gal water |
24 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) |
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COMMENTS: Rates per 100 gal of water vary with manufacturer;
always check label for recommended rate. Kills twig lesions. Do not apply
after cluster
bud.
Sulfur used before bloom reduces crop set in Anjou and Comice. It is
phytotoxic to Comice and should not be used on this variety. Caution: Do not
apply within 3 weeks of an oil application. Lime sulfur is incompatible with most other pesticides; check before use. |
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| K. |
LIME SULFUR# |
2 gal/100 gal water |
48 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) |
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COMMENTS: Kills twig lesions. Do not apply after cluster bud.
Sulfur used before bloom reduces crop set in Anjou and Comice. It is
phytotoxic to Comice and should not be used on this variety. Caution: Do not
apply within 3 weeks of an oil application. Phytotoxicity may occur any time
weather is hot so watch weather conditions closely. Lime sulfur is incompatible with most other pesticides; check before use. |
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| L |
ZIRAM 76DF |
6–8 lb/acre |
48 |
5 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3) |
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COMMENTS: Important in a resistance management program. Do not apply more than 32 lb/acre/crop cycle. |
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| POSTHARVEST |
| A. |
LIME SULFUR# |
5–6 gal/100 gal water |
48 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) |
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COMMENTS: Do not apply any sooner than November 1 and only on
trees not suffering from moisture stress. Kills twig lesions. Phytotoxicity
may occur anytime weather is hot, so watch weather conditions closely. Lime
sulfur is incompatible with most other pesticides. Check before use. Apply
with or without oil (5 gal/acre) but do not apply with oil before November 15. When applied with oil, maximum lime sulfur rate per acre is 5 gal. |
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UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455
Diseases
R. B. Elkins, UC Cooperative Extension, Lake Co.
W. D. Gubler, Plant Pathology, UC Davis
L.G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma Co.
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