Agriculture: Pear Pest Management Guidelines

Lygus Bugs

  • Pale legume bug: Lygus elisus
  • Western tarnished plant bug: Lygus hesperus
  • Description of the Pest

    Lygus bug damage may occur in all major pear districts but is mostly a pest in the Delta region. Lygus damage is more frequent in orchards having permanent cover crops and in orchards adjacent to crops or vegetation hosting 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 adult is about 0.25 inch (6 mm) long and 0.1 inch (2.5 mm) wide, with wing tips that bend down. Nymphs resemble adults, but are smaller and do not have wings. Five black spots are visible on the back on later nymphal instars.

    Damage

    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.

    Management

    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 feed on fruit, causing damage 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 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 or tomato fields are at a greater risk for damage and lygus infestations may coincide with cuttings or harvest.

    Organically Acceptable Methods

    Cultural control is an organically acceptable method.

    Monitoring and Treatment Decisions

    If an orchard has had a history of lygus damage, 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. 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** REI‡ PHI‡
    (Example trade name) (conc.) (dilute) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
     
    A. FENPROPATHRIN*
      (Danitol 2.4EC) 16–21.33 fl oz 4–5.3325 fl. oz. 24 14
      MODE OF ACTION GROUP NUMBER1: 3A
      COMMENTS: Harmful to beneficial insects and mites; will suppress spider mites. Do not apply to blooming plants, including fruit trees and broadleaf weeds.
     
    B. LAMBDA-CYHALOTHRIN*
      (Warrior with Zeon) 2.56-5.12 fl oz 24 21
      MODE OF ACTION GROUP NUMBER1: 3A
      COMMENTS: Harmful to beneficial insects and mites; will suppress spider mites. May cause outbreaks of pear rust mite. Do not apply to blooming plants, including fruit trees and broadleaf weeds.
     
    C. CLOTHIANIDIN
      (Clutch 50WDG) 2–6 oz 12 7
      MODE OF ACTION GROUP NUMBER1: 4A
      COMMENTS: Do not apply to blooming plants, including fruit trees and broadleaf weeds.
     
    D. ACETAMIPRID
      (Assail 70WP) 1.1–3.4 oz 12 7
      MODE OF ACTION GROUP NUMBER1: 4A
     
    E. THIAMETHOXAM
      (Actara) 4.5–5.5 oz 1.125–1.375 oz 12 see comments
      MODE OF ACTION GROUP NUMBER1: 4A
      COMMENTS: 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. Do not apply to blooming plants, including fruit trees and broadleaf weeds.
     
    F. IMIDACLOPRID
      (Provado 1.6F) 10 fl oz 2.5 fl. oz 12 7
      MODE OF ACTION GROUP NUMBER1: 4A
      COMMENTS: Effective against boxelder and lygus bugs, but not stink bugs. Do not apply to blooming plants, including fruit trees and broadleaf weeds.
     
    G. DIMETHOATE Label rates see label 28
      MODE OF ACTION GROUP NUMBER1: 1B
      COMMENTS: May kill beneficial mites and pear psylla predators. Do not apply to blooming plants, including fruit trees and broadleaf weeds. Not allowable by some processors, so check first.
    ** Dilute rate is the rate per 100 gal water; use 400 gal solution/acre. Apply concentrate in 80–100 gal wate/ acre, or less if the label allows.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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).
    Not recommended or not on label.
    Text Updated: 11/12
    Treatment Table Updated: 11/12