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UC Pest Management Guidelines


Adult lygus bug, Lygus hesperus.

Apple

Lygus Bugs

Scientific Names: Lygus hesperus and Lygus elisus

(Reviewed 8/06, updated 3/09)

In this Guideline:


DESCRIPTION OF THE PESTS

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 long and 0.1 inch wide, flattened on the back. Nymphs resemble adults, but are smaller and do not have wings.

DAMAGE

Lygus bug damage may occur in all major apple districts and sometimes is severe. Lygus attack is more frequent in orchards that have a permanent cover crop and in orchards adjacent to crops or vegetation that host lygus.

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. Midseason feeding results in round pits, and late-season feeding causes irregularly-shaped depressions that are similar to stink bug damage.

MANAGEMENT

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. In orchards with a history of lygus damage, monitor fruit at least biweekly between petal fall and harvest to assess need for treatment.

Biological Control
The role of predators and parasites in controlling lygus in orchards has not been investigated, but in cotton and strawberries, beneficials have been shown to be helpful.

Cultural Control
Eliminate or suppress weed host plants before fruit forms on trees and thereafter throughout the growing season to minimize lygus populations. Yellow starthistle, Russian thistle, tarweed, sweet clover, wild mustard, lambsquarters, pigweed, shepherd's-purse, wild radish, and vetch are important hosts. Do not mow cover crops or weeds when lygus bugs are present or they will move into the trees.

Organically Acceptable Methods
Cultural and biological control are organically acceptable.

Monitoring and Treatment Decisions
After fruit has formed, sample the cover crop with a sweep net to determine if lygus bugs are present in the orchard. If they are, or 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. Lygus bugs may be present in the orchard but not feeding on the fruit, so you need to check the fruit for damage. Examine a minimum of 100 fruits from trees throughout the block. Because lygus damage is often spotty in distribution, check each 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 apple in 100 is significant for concern and calls for further sampling and evaluation of control needs. 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. Especially be on the lookout for lygus when weeds start to dry up. 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 border trees will hold down numbers and reduce damage.

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

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees and environmental impact.
 
A. ACETAMIPRID
  (Assail) 3.4 oz 0.85 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 4A
  COMMENTS: Do not make more than 4 applications/season. Do not exceed 13.5 oz/acre/crop. Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail; imidacloprid- Provado; and thiacloprid-Calypso) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance.
   
B. IMIDACLOPRID
  (Provado) 1.6F 8 fl oz 2 fl oz 12 7
  MODE OF ACTION GROUP NUMBER1: 4A
  COMMENTS: Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail; imidacloprid- Provado; and thiacloprid-Calypso) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance.
   
C. DIMETHOATE Label rates 48 28
  MODE OF ACTION GROUP NUMBER1: 1B
   
D. FORMETANATE HYDROCHLORIDE
  (Carzol) SP 1 lb 4 oz 16 days 0
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Do not apply more than 1.25 lb/acre/season. Do not apply after petal fall. See label for second application restrictions.
   
** For dilute application, rate is per 100 gal water to be applied in 300-500 gal water/acre, according to label; for concentrate applications, use 80-100 gal water/acre or lower 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.
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 http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Apple
UC ANR Publication 3432
Insects and Mites
J. L. Caprile, UC Cooperative Extension, Contra Costa County
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
P. M. Vossen, UC Cooperative Extension, Sonoma and Marin counties
W. W. Coates, UC Cooperative Extension, San Benito County
H. L. Andris, UC Cooperative Extension, Fresno County
L. G. Varela, UC IPM Program, Sonoma County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, Sutter and Yuba counties

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