How to Manage Pests

UC Pest Management Guidelines

Alfalfa

Threecornered Alfalfa Hopper

Scientific Name: Spissistilus festinus

(Reviewed 1/17, updated 1/17)

In this Guideline:


Description of the Pest

The threecornered alfalfa hopper adult is a green, robust, wedge-shaped insect with clear wings. The body is about 0.25 inch (6.4 mm) long, is higher and wider at the head and tapers towards the end. This insect gets its name from the hardened triangular (three-cornered) area over the thoracic area as seen from above. It has piercing-sucking mouthparts. Nymphs are grayish white and soft bodied, with a line of saw-toothed spines on their backs. Adults are mobile whereas nymphs cannot fly and are confined to the lower portions of the plant.

Adults feed on numerous plants and have been recently shown to transmit red blotch in grape vineyards. In alfalfa, threecornered alfalfa hoppers can be found year-round. In the low desert, there are two population peaks for adults: one in late July to early August and a larger second peak in September to early October. In the San Joaquin Valley, threecornered alfalfa hoppers numbers usually peak in late September and October. They are starting to become more numerous in the Sacramento Valley, usually late August to early September. There are three to four generations per year in Southern California.

Damage

Adults and nymphs of the alfalfa hopper usually feed at the base of the alfalfa plant near the crown by inserting their mouthparts into stems and sucking out juices. Injury is also caused when adult female hoppers insert their eggs into stems. Feeding and egg laying can girdle stems, causing the portion of the plant above the girdle to turn red, purple or yellow.

Management

Monitor for adults using a sweep net and by visually watching for stems that show the characteristic reddish discoloring and girdling at the base of the plant. Nymphs are difficult to find because they are at the base of the plant and cannot fly. Occasionally damage is severe enough from the hoppers to justify control measures, especially if other pests, such as armyworm are also injuring the crop. However, this insect does not inject toxins, unlike the Empoasca, so they are not as damaging as some leafhopper pests.

Biological Control

Biological control of threecornered alfalfa hopper is generally limited to the first three nymphal instars, which remain inactive lower on the alfalfa plants. Predators include assassin and nabid bugs. Adult hoppers typically escape predation due to their activity and heavy sclerotization (hardening of the exoskeleton), which nymphs lack.

Cultural Control

Overwintering threecornered alfalfa hopper adults and newly hatched nymphs can be found in weedy margins (e.g. vetch) of alfalfa fields in the early spring. Manage these areas to reduce threecornered alfalfa hopper populations that can later migrate into alfalfa fields. Early harvest will also help manage this pest.

Monitoring and Treatment Decisions

No specific threshold numbers have been developed for threecornered alfalfa hoppers. However, in the Sacramento Valley area, an average of four leafhopper adults per sweep over 15 days did not cause economic losses to alfalfa hay; but, in the south valley, 10 to 12 hopper adults per sweep significantly reduced both alfalfa yield and quality. These numbers give a range of hopper counts for possible injury to the alfalfa crop and should be combined with observations of damage to determine whether to treat with insecticides listed below. Early spring alfalfa stubble insecticide applications after the first cutting are a viable option to manage threecornered alfalfa hoppers long term in outbreak years.

Common name Amount per acre** REI‡ PHI‡
(Example trade name)   (hours) (days)

UPDATED: 12/16
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. BETA-CYFLUTHRIN*
  (Baythroid XL) 1.6-2.8 fl oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Do not apply to alfalfa grown for seed because of the potential for injury to bees.
 
B. 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. Apply only to fields planted to pure stands of alfalfa. Do not apply when bees are actively foraging.
 
C. METHOMYL*
  (Lannate LV) 1.5 pt 48 7
  (Lannate SP) 0.5 lb 48 7
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: Do not graze or feed livestock for 7 days after application. Do not apply when bees are present.
 
D. PERMETHRIN*
  (Pounce 25WP) 6.4–12.8 oz 12 See label
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Do not use more than 0.2 lb a.i./cutting. Do not apply to mixed stands with intentionally grown forage grasses and legumes.
 
** 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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