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How to Manage Pests

UC Pest Management Guidelines


Adult devastating grasshopper.

Avocado

Grasshoppers

Scientific name:
Devastating grasshopper: Melanoplus devastator
Valley grasshopper: Oedaleonotus enigma

(Reviewed 1/07, updated 8/08)

In this Guideline:


DESCRIPTION OF THE PESTS

Grasshoppers (order Orthoptera) are robust, elongate insects with winged adults that are good flyers. Commonly they are brown, gray, green, or yellowish insects with greatly enlarged hind-leg femurs adapted for jumping. Grasshoppers have relatively short antennae, which distinguishes them from crickets, katydids, and other Orthoptera, which have long antennae.

Most species of grasshopper overwinter as eggs and have only one generation a year. Adults live and feed for 2 to 3 months, during which females typically deposit elongate pods of about 20 to 100 eggs in the topsoil of undisturbed areas. Eggs hatch when soil warms in spring. The nymphs feed on most any species of nearby green plant, molting five or six times before becoming adults.

Nymphs and adults readily move. Each individual typically feeds on several different plants. As vegetation is consumed or dries when the rainy season ends, grasshoppers migrate to succulent plants. Adults, sometimes in a large swarm, can fly several miles a day. Nymphs readily jump, walk, or are carried by wind.

Grasshopper populations vary from year to year. Grasshoppers become more numerous after warm, moist springs produce abundant vegetation in uncultivated areas, favoring grasshopper survival. Conversely, parasites and bacterial, fungal, and protozoan diseases can cause grasshopper populations to crash. Many grasshoppers are eaten by arboreal predators such as birds and robber flies (family Asilidae) and soil-dwelling egg predators such as blister beetles (Meloidae).

DAMAGE

Grasshoppers become economic pests when young tree foliage is extensively chewed by large numbers of insects migrating from unmanaged vegetation. Mature trees are not harmed by grasshopper feeding.

MANAGEMENT

Do not take control action based solely on damage. Caterpillars, earwigs, Fuller rose beetle, June beetles, and snails also chew leaves. Some management methods vary depending on the cause. Where abundant, grasshoppers can be observed during the day feeding openly and flying or jumping among plants.

Grasshoppers can be difficult to manage once large numbers move onto young trees. If you believe grasshoppers may become a problem, monitor for them in uncultivated areas near young trees. Before adjacent vegetation dries or is cut, consider applying insecticide combined with bait or spraying border areas to kill grasshoppers before they migrate and start to damage crops.

Common name Amount to use R.E.I.+ P.H.I.+
(trade name)   (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. Not all registered pesticides are listed. Always read label of product being used.
         
A. MALATHION 8
4–9 pt/acre
12
7
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Only treat infested trees to avoid destroying natural enemies of mites, loopers, scales, and other potential secondary pests.
   
+ 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: Avocado
UC ANR Publication 3436
Invertebrates
B. A. Faber, UC Cooperative Extension, Santa Barbara/Ventura counties
J. G. Morse, Entomology, UC Riverside
M. S. Hoddle, Entomology, UC Riverside
Acknowledgment for contributions to Invertebrates:
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
M. Blua, Entomology, UC Riverside
P. Oevering, UC Cooperative Extension, Ventura County
D. Machlitt, Consulting Entomology Services, Moorpark, CA
T. Roberts, Integrated Consulting Entomology, Ventura, CA
B. B. Westerdahl, Nematology, UC Davis

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