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How to Manage Pests

UC Pest Management Guidelines


Omnivorous looper larva

Avocado

Monitoring Caterpillars and their Natural Enemies

(Reviewed 1/07, updated 6/10)

In this Guideline:


Caterpillars are the larvae of moths and butterflies (order Lepidoptera). Omnivorous looper, western avocado leafroller (amorbia), and (least frequently) orange tortrix are sporadic pests in avocado. Healthy trees can tolerate some loss of chewed foliage and blossoms. Extensive defoliation can result in sunburn to fruit and twigs. Economic damage occurs primarily when caterpillars chew and scar fruit. Conserve natural enemies, as caterpillars are usually under effective biological control.

IDENTIFYING CATERPILLARS AND NATURAL ENEMIES

SAMPLING CATERPILLARS AND THEIR NATURAL ENEMIES

  • From March through August, monitor at least 10 trees per grove about every 7 to 10 days, concentrating efforts in areas where you see leaf chewing or found caterpillars the previous season.
  • Sample caterpillars using timed counts or foliage shaking, as described below, depending on the prevalent species.
  • For all samples combined from each tree, record the total number of caterpillars and the total predators of caterpillars.
  • Record separately any apparently diseased and parasitized caterpillars, also record any diseased or parasitized larvae in the caterpillars per hour or caterpillars per 25 shakes column. (This "double counting" prevents the caterpillar pressure calculation from being altered by variations in the ratio of predators to diseased or parasitized caterpillars.)
  • If it is not obvious whether a caterpillar is healthy versus diseased or parasitized, or if you don't know if the observed species are predators of caterpillars, collect those specimens for closer examination later. This is especially important when conducting timed counts, so time is not diverted from inspecting trees during the fixed monitoring time.

Using the Shake Method
Shake foliage to sample avocado looper:

  1. Place a 1-yard square collecting surface (e.g., cloth or flattened cardboard box) beneath outer canopy foliage.
  2. Vigorously shake small limbs to dislodge caterpillars onto the collecting surface. (For example, shake foliage on 2 or 3 separate sections of each tree to collect 25 shake samples.)

Using the Timed Method
Make timed counts for amorbia (western avocado leafroller), avocado looper, and orange tortrix.

  1. Spend a fixed amount of time inspecting foliage for caterpillars. For example, spend 6 minutes inspecting each of 10 trees (1 hour).
  2. Use an alarm watch or timer to ensure the entire period is spent monitoring, and that time spent moving among distant trees is not included.
  3. Walk slowly around the outer canopy, looking for chewed and webbed foliage or fruit. Pull apart webbing and count any caterpillars and natural enemies.
  4. Record results on a caterpillar and biological control sampling form (70 KB, PDF).

MONITORING ADULT MOTHS

Adult moths are nocturnal and consume only liquids and pollen. During the day they rest on the underside of leaves or on shady bark.

  • Deploy pheromone-baited sticky traps for adults to identify the species in groves and indicate peaks in flights of egg-laying adults. Each trap is baited with a separate pheromone to attractU adult male amorbia, omnivorous looper, or orange tortrix. For amorbia, two different pheromones are used, one for northern California and the San Joaquin Valley and another for southern California including Ventura County. Unless other methods are recommended, deploy traps at a density of about one trap per ten acres when adult moths are expected to be present. Check with suppliers for recommended pheromones and the type and number of traps to use.
  • Trapping moths can indicate that foliage monitoring is warranted and helps to time management actions such as release of Trichogramma egg parasites. Adult traps generally are not useful for determining need for treatment, partly because caterpillars are the damaging stage and natural enemies kill many eggs and larvae relative to the moth population that is trapped earlier in the season.

IMPORTANT LINKS

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
General Information
Acknowledgment for contributions to General Horticultural Information:
M. L. Arpaia, Botany and Plant Sciences, UC Riverside
M. L. Bianchi, UC Cooperative Extension, San Luis Obispo County
C. J. Lovatt, Botany and Plant Sciences, UC Riverside
P. Mauk, UC Cooperative Extension, Riverside County
G. W. Witney, California Avocado Commission, Irvine, CA

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