How to Manage Pests

UC Pest Management Guidelines

Alfalfa

Leafhoppers

Scientific Names:
Garden leafhopper: Empoasca solana
Potato leafhopper: E. fabae
Mexican leafhopper: E. mexara

(Reviewed 1/17, updated 1/17)

In this Guideline:


Description of the Pests

Several species of Empoasca leafhoppers occur in alfalfa. They all have the same general overall appearance: small [0.125 inch (3.2 mm) long], bright green, wedge-shaped bodies. Nymphs (immatures) also have green wedge-shaped bodies and run rapidly when disturbed. They may run forward, backward, or from side to side. Their curious movement plus their shape serve to distinguish them from lygus bug nymphs and slower moving aphids. Other green leafhoppers may be present in alfalfa, such as the threecornered alfalfa hopper, but they are much larger in size. Other small leafhoppers found in alfalfa are brown or gray in color and do no apparent damage.

Damage

The most common damage symptom is a yellow, wedge-shaped area at the tip of the leaf known as 'hopperburn'. Frequently, the leaf margin and tissue surrounding this area turns red. This symptom may occasionally be confused with boron deficiency but can easily be distinguished from it by the presence of the insects. Empoasca leafhoppers also inject a toxin into the plants, which can cause stunted plants with very short internodes. Stunting and yellowing may persist into the next cutting cycle, even in the absence of leafhoppers.

Although Empoasca leafhoppers may be found throughout the year, damage in the Central Valley is generally found during July, August, and occasionally September. In the Imperial Valley, damage may occur from May through September; infestations are often adjacent to or upwind from sugarbeets. Some years this insect is a major pest, other years it is not. Its cyclical nature may be associated with warmer winters where they overwinter in fields or they may be migrating in from other areas.

Management

Scheduling an early cutting can effectively manage damaging leafhopper populations, otherwise insecticide treatment may be warranted.

Cultural Control

If alfalfa is within a few days of harvest, early cutting will control Empoasca leafhoppers.

Organically Acceptable Methods

Only cultural controls are acceptable for use on an organically certified crop.

Monitoring and Treatment Decisions

Check the field in July and August (and if necessary into September) to see if leafhoppers are present, especially for fields that are re-growing after harvest. At the first sign of injury, sample the field with a standard sweep net. For stubble fields, watch for damage when walking across the field, including: stunting of plants, poor regrowth, and high leafhopper numbers. Leafhopper infestations usually begin on the field margin so be sure to include field edges in your samples.

  • Sample four areas over the entire field by taking five sweeps in each area and counting the number of adults and nymphs.
  • Record observations on a monitoring form (PDF).
  • If alfalfa is 2 or more weeks away from harvest: apply insecticides if counts reach five leafhoppers per sweep (adults and nymphs combined).
  • If alfalfa is scheduled for harvest in 10 days to 2 weeks: apply insecticide if counts reach ten per sweep.

For information on sweep sampling, see the SAMPLING WITH A SWEEP NET section.

Leafhopper damage on stubble fields can be much more severe and the toxins they inject can stunt the plants, arresting growth and reducing yields. In these situations, threshold levels may be low. As a result, it is important to visually look at fields for the presence of leafhoppers and damage on newly cut stands. Often, leafhopper infestations with high enough numbers to justify treatment are confined to the first 50 to 100 feet of the field margin. If this is the case, apply insecticide only to the field edges where high leafhopper counts are found.

Common name Amount per acre** REI‡ PHI‡
(Example trade name)   (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
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. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. FLUPYRADIFURONE
  (Sivanto 200SL) 7–10.5 fl oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 4D
 
B. PERMETHRIN*
  (Pounce 25WP, Ambush 25W) 6.4–12.8 oz 12 See label
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Do not apply when bees are present.
 
C. DIMETHOATE
  (Dimethoate 400) 0.5–1 pt 48 See comments
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: Check label to see if product allows only one application per year or per cutting. Preharvest interval (PHI) is 10 days for harvest or pasturing; for alfalfa seed: do not feed or graze livestock on treated crops, hay threshings, or stubble within 20 days of application. Do not apply when bees are present.
 
D. CHLORPYRIFOS*
  (Lorsban Advanced) 0.5–1 pt 24 7 (0.5 pt); 14 (1 pt)
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: Do not make more than 4 applications per year or apply more than once per crop cutting. Do not apply when bees are present. Avoid drift and tailwater runoff into surface waters. Certain formulations emit high amounts of volatile organic compounds (VOCs); use low-VOC formulations. Regulations affect use for the San Joaquin Valley from May 1 to October 31, 2017. Review the Department of Pesticide Regulation's updated fact sheet.
 
E. ZETA-CYPERMETHRIN*
  (Mustang) 2.4–4.3 fl oz 12 See comments
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Preharvest interval is 3 days for cutting and grazing and 7 days for seed.
 
F. METHOMYL*
  (Lannate LV) Label rates 48 7
  (Lannate SP) Label rates 48 7
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: Do not apply when bees are present.
 
G. LAMBDA-CYHALOTHRIN*
  (Warrior II with Zeon) 0.96–1.6 fl oz 24 See comments
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Preharvest interval (PHI) is 1 day for forage and 7 days for hay. Do not apply when bees are actively foraging.
 
H. BETA-CYFLUTHRIN*
  (Baythroid XL) 0.8–1.6 fl oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Do not apply to alfalfa grown for seed because of potential for injury to bees.
 
** See label for dilution rates.
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).

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430

Insects and Mites

L. D. Godfrey, Entomology, UC Davis
E. T. Natwick, UC Cooperative Extension, Imperial County
P. B. Goodell, Entomology, Kearney Agricultural Center, Parlier
R. F. Long, UC Cooperative Extension, Yolo County
V. M. Barlow, UC Cooperative Extension, Riverside County and UC IPM Program

Acknowledgment for contributions to Insects and Mites:
D. R. Haviland, UC Cooperative Extension, Kern County
M. Rethwisch, UC Cooperative Extension, Riverside County (Blythe)
C. G. Summers, Entomology, Kearney Agricultural Center

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