How to Manage Pests

UC Pest Management Guidelines

Leaf blisters from pearleaf blister mite feeding.

Pear

Pearleaf Blister Mite

Scientific name: Eriophyes (=Phytoptus) pyri

(Reviewed 11/12 , updated 11/12 )

In this Guideline:


DESCRIPTION OF THE PEST

Adult mites are very small, about the same size as rust mites, and cannot be seen without a 14 to 20X hand lens. The body is white, long and slender, striated, and with a few long hairs. Immature forms resemble adults but are smaller. Eggs are spherical and pearly white.

DAMAGE

Pearleaf blister mites feed under the bud scales during winter and may cause buds to dry and fail to develop in spring. When buds start to grow in spring, mites feed on emerging leaves from green tip through bloom and also on developing fruit. Feeding on fruit results in oval russet spots, usually depressed with a surrounding halo of clear tissue. These spots are 0.25 to 0.50 inch in diameter and frequently run together. When damaged fruit matures, it is often deformed and misshaped. Leaf feeding causes small blisters, 0.125 (3 mm) to 0.25 inch (6 mm) across, which are first red and later turn black. Leaf function can be seriously impaired. Eggs are laid in the blisters and young mites feed inside the blister, thus they are rarely seen.

MANAGEMENT

Pearleaf blister mites occur throughout pear-growing areas in California. Abandoned and unsprayed young pear trees are subject to severe, periodic blister mite infestations. Blister mite has increased in orchards under long-term mating-disruption programs, especially those adjacent to abandoned or unsprayed orchards. Monitor and treat in fall or dormant season. IPM practices minimize damage by this pest; the use of pyrethroids may increase blister mite damage.

Resistant Varieties

Pears with naturally russetted surfaces (Bosc, Hardy, Winter Nelis) do not show the effects of blister mite attack.

Organically Acceptable Methods

Sulfur sprays and oil sprays after harvest are organically acceptable methods.

Monitoring and Treatment Decisions

Blister mite may be sampled during the dormant season. Using a 14 to 20Xhand lens, examine terminal buds on 100 shoots (one from the treetop and one from eye level of 50 trees per 20-acre block), and inspect the first several scales on each bud for the presence of mites.

Most of the overwintering blister mites are found beneath the outer bud scales in October and November and are readily controlled with a fall spray. The presence of any mites indicates the need for control. As the season progresses, control becomes more difficult. (For more information regarding dormant sampling, see DORMANT TO DELAYED-DORMANT SAMPLING.

Sampling top shoots is the best method for predicting a damaging blister mite population. Collect samples before, during, or after harvest. Collect one shoot from the top and one from eye level from 20 vigorous trees in a block, as described in SAMPLING DURING FRUIT DEVELOPMENT and POSTHARVEST SURVEY. Inspect the shoots for the presence of blisters. When three or more top shoots show damage, fruit damage can be expected the following spring if treatments are not applied either postharvest or during dormancy.

Harvest fruit sample

At harvest, assess your IPM program by monitoring fruit in the bins for pearleaf blister mite damage. Sample 200 fruit per bin from 5 bins per orchard (or 20-acre blocks in large orchards). For more information, see HARVEST FRUIT SAMPLE.

Common name Amount to use** R.E.I.+ P.H.I.+
(trade name) (conc.) (dilute)
(hours) (days)

  Calculate impact of pesticide on air quality
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. Not all registered pesticides are listed. Always read the label of the product being used.
 
DORMANT
A. NARROW RANGE OIL# 8 gal 1.5–2 gal 4 0
  . . . or . . .
  DORMANT FLOWABLE EMULSION 6–8 gal 2–3 gal 4 0
  . . . or . . .
  DORMANT PLUS 6–8 gal 2–3 gal 4 0
  MODE OF ACTION: Contact, including smothering and barrier effects.
  COMMENTS: Apply during warm, sunny weather from leaf fall to start of egg laying for best results. Do not apply oil in the dormant season until root zone is wet from rain or irrigation. Apply oil in late morning when dew or rain has dried from the bark. Do not apply oil after a period of drying wind or extreme cold. For narrow range oil, check with your certifier to determine which products are organically acceptable.
 
GREEN TIP TO FINGER BUD
A. LIME SULFUR# 6 gal 1.5 gal 48 0
  MODE OF ACTION: Unknown. An inorganic miticide.
  COMMENTS: Do not use on Anjou or Comice. Do not use within 10 days of oil. Do not apply when maximum daily temperatures exceed 75°F.
 
B. LIME SULFUR# 6 gal 1.5 gal 48 0
  . . . PLUS . . .
  MICRONIZED SULFUR# 16 lb 4 lb 24 0
  MODE OF ACTION: Unknown. An inorganic miticide.
  COMMENTS: Do not use on Anjou or Comice. Do not use within 10 days of oil. Do not apply when maximum daily temperatures exceed 75°F.
 
FINGER BUD TO 10% BLOOM
A. MICRONIZED SULFUR# 20 lb 5 lb 24 0
  MODE OF ACTION: Unknown. An inorganic miticide.
  COMMENTS: Can be applied when maximum daily temperatures do not exceed 90°F. Do not use within 10 days of oil.
 
POSTHARVEST
A. DIAZINON* 50WP 3 lb 1 lb 96 (4 days) 21
  MODE OF ACTION: 1B
  COMMENTS: Avoid drift and tailwater runoff into surface waters. Do not apply to blooming plants, including fruit trees and broadleaf weeds.
 
MID- TO LATE NOVEMBER
A. LIME SULFUR# 4 gal 1 gal 48 0
  MODE OF ACTION: Unknown. An inorganic miticide.
  . . . PLUS . . .
  NARROW RANGE OIL#
  (Supreme, Superior) 4–6 gal 1.5 gal 4 0
  MODE OF ACTION: Contact, including smothering and barrier effects.
  COMMENTS: Do not apply lime sulfur and oil spray any sooner than November 15 and only on trees not suffering from moisture stress. Phytotoxicity may occur any time the weather is hot so watch weather conditions closely. Check with your certifier to determine which products are organically acceptable.
 
B. LIME SULFUR# 2 gal 0.5 gal 48 0
  . . . PLUS . . .
  MICRONIZED SULFUR# 16 lb 4 lb 24 0
  MODE OF ACTION: Unknown. An inorganic miticide.
  COMMENTS: Apply in October after temperatures cool.
 
** Dilute rate is the rate per 100 gal water; use 400 gal solution/acre. Apply concentrate in 80–100 gal water/acre, or less if the label allows.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals with a different mode of action Group number, and do not use products with the same mode of action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at www.irac-online.org.
# Acceptable for organically grown produce.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455

Insects and Mites

L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County
R. B. Elkins, UC Cooperative Extension, Lake County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
C. Ingels, UC Cooperative Extension, Sacramento County
Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter/Yuba counties
P. W. Weddle, Weddle, Hansen & Associates
R. Hansen, Weddle, Hansen & Associates
P. Chevalier, United Ag Products, Ukiah
M. Hooper, Ag Unlimited, Lakeport
B. Knispel, Pest Control Adviser, Upper Lake
T. Lidyoff, Purity Products, Healdsburg
G. McCosker, Harvey Lyman Agservices, Walnut Grove
B. Oldham, Ag Unlimited, Ukiah
J. Sisevich, AgroTech, Kelseyville (retired)
D. Smith, Western Farm Service, Walnut Grove
B. Zoller, The Pear Doctor, Inc., Kelseyville

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