Date Last Edited: 08/24/2001
Hawaii Cooperative Extension Service
This report describes each pest and summarizes the results of efficacy tests conducted at the University of Hawaii at Manoa, Waiakea Experiment Station in Hilo, Hawaii.
Palm mealybug on Rhapis excelsa:
White waxy material secreted by the mealybugs are easily detected in the rhapis terminals. Adults and nymphs are found between the stem and rhapis fibers. Fast moving adults are often seen crawling on the foliage. Infestations are usually found when plant s are neglected or have not been sprayed for awhile.
Root infesting mealybugs:
Prior to 1990, the major mealybug species causing shipment rejection from Hawaii was the coffee root mealybug, Geococcus coffeae. Since 1990, Rhizoecus hibisci, new to Hawaii, has spread to major potted foliage production areas. In addition, R. caladii has been recently intercepted by California in Rhapis palms from Hawaii.
Root infesting mealybugs occur throughout the root mass; however, they are concentrated between the root ball and the pot. Slow growing plants or pots that are root bound are more likely to get infested.
Infestations of root infesting mealybugs are noticeable only if pots are removed. Insecticide penetration is impeded by the pot, media, root ball, and waxy secretion from their bodies. Plant species and growing media also affect the effectiveness of insec ticides.
Female mealybugs secrete a white waxy material and are usually visible between the pot and the root ball. Female mealybugs lay eggs or give birth to live young (crawlers). If eggs are laid, they usually hatch in less than 24 hours. Crawlers are the disper
sal stage and are highly mobile. Once the crawlers find a suitable site, they settle down and begin to feed. The entire life cycle ranges from 2-4 months depending on species. Adults live from 27-57 days, depending on species.
Preventing the spread and establishment of root infesting mealybugs:
Because the root mealybug is a difficult pest to control, every effort should be made to prevent establishment. The following practices are recommended to prevent establishment and spread:
Chemical control of R. hibisci on Rhapis excelsa:
One application of Marathon 1G significantly reduced the mean number of mealybugs per pot. Marathon treated pots averaged 12 mealybugs per pot whereas the untreated pots averaged 70 mealybugs per pot 52 days after treatment.
Insecticide drenches were evaluated for efficacy in two ways--with the pots on and with the pots removed. This was done to determine how much the pot impeded insecticide penetration. Efficacy was evaluated by dissecting the root ball, recovering all mealy bugs, and observing for movement under a dissecting microscope. Visual assessment (unaided eye) in the field is not sufficient to determine mealybug mortality.
"Hawaii pesticide law prohibits the use of many insecticides as drenches. Pesticide labels which prohibit drench usage or state the amount of product to be used per acre such as Talstar 8.0F in this study cannot be legally used as drenches. Used drench solutions should be disposed by applying to approved crops or site in accordance with all label directions. Contact the Hawaii Department of Agriculture, Pesticide Branch if in doubt about legal use and proper disposal of insecticide drench solutions."Top of Page
Hot-water Treatment of R. hibisci on Rhapis excelsa:
Additional phytotoxicity and efficacy research is needed to determine the thermal death requirement of R. hibisci and heat tolerance of various plant species. Preliminary studies indicate that Rhapis palms may tolerate heat treatments.
Slug management strategy:
The following suggestions may increase efficacy of slug control programs:
The brown slug, Vaginula plebeia Fischer, and two-striped slug, Veronicella cubensis (Pfeiffer), continue to increase in Hawaii, causing severe damage to flowers and foliage. The brown slug was first reported in Hawaii in 1976 on the island of Hawaii. Its color ranges from beige to dark brown. The two-striped slug, with two longitudinal stripes on its back, was first reported on Oahu in 1985. Its color may also vary from beige to dark brown, and its stripes may be solid or broken.
There are many methods to control slugs including:
Slug baits are a popular and effective method to control slugs that forage on the ground. Most slug baits contain up to 4% metaldehyde. Metaldehyde acts as both a contact and stomach poison. In low doses metaldehyde causes slugs to oversecrete mucus, resu lting in desiccation. In high doses metaldehyde acts as a nerve poison. Methiocarb (Mesurol) is another active ingredient found in molluscicides belonging to the carbamate class of insecticides. Unfortunately, methiocarb will no longer be manufactured, re sulting in the loss of several effective slug products.
Molluscicide sprays are most effective when slugs live aboveground or do not actively forage on the ground. However, because metaldehyde rapidly degrades in sunlight, thorough coverage and evening applications are important. In addition, certain formulati ons of liquid metaldehyde contain tallow (fat) as a attractant. These products have a short shelf life and should be bought as a need arises.
The effectiveness of copper barriers is short-lived in Hawaii because of our high humidity. Once the copper tarnishes, the barrier is no longer effective.
Slug traps or hand picking of slugs may be economical in home gardens but not in commercial production. Slug populations in heavily infested areas number in the thousands per acre.
Slugs are hermaphroditic--they possess both male and female sex organs. A majority of species need to mate. Once slugs mate, both slugs may lay eggs. Depending on the species, 10-200 eggs are laid which hatch in 14 to 30 days. Juveniles reach sexual matur
ity in 3-5 months and may take as long as 2 years to become full grown. Juveniles and slugs past the reproductive stage are the most difficult to control.
Bioassay tests of molluscicides against the brown slug and the two-striped slug:
Brown Slug, Vaginula plebeia
Deadline Granules 81% Corry's Slug and Snail 42% Deadline Bullets 76% Deadline One Last Meal 41% Hacco AG 3.5 62% Corry's Slug & Snail Killer 38% Metaldehyde/Methiocarb 60% Ortho Bug-Geta Plus 35% Ortho Bug-Geta 58% Corry's Slug & Snail Death 26% RCO Slug and Snail 55% Ortho Slug-Geta* 20% RCO Rain Resistant 48% Deadline 40 18% Durham Metaldehyde 7.5G 48% Corry's Liquid S/S Control 14% Durham Metaldehyde 3.5G 47% Corry's S/S Insect Killer 7%
Efficacy against the two-striped slug were as follows:
Two-striped slug, Veronicella cubensis
Deadline Granules 84% Ortho Slug-Geta 36% Deadline Bullets 66% Metaldehyde/Methiocarb 33% Durham Metaldehyde 7.5G 63% Deadline OLM 30% Hopkins AG 3.5 60% Durham Metaldehyde 3.5G 28% RCO Slug and Snail 45% Corry's S/S Killer 27% Corry's Slug and Snail 45% Deadline 40 18% Corry's S/S Death 43% Corry's Liquid S/S Control 18% Ortho Bug-Geta 41% Corry's S/S Insect Killer 17% RCO Rain Resistant 40% Ortho Bug-Geta Plus 12%
Tests were conducted to evaluate the effectiveness of various molluscicides. Field collected slugs were held in a glass aquarium with a screen cover and fed 'Iceberg' lettuce daily until tests began. A 3-inch thick layer of peat covered the bottom of the aquarium.
Molluscicides were applied at their recommended label rates to 1 ft^2 plexiglass cages. Immediately after treatment, 10 slugs were added to each cage. Each cage contained a l-inch thick layer of peat moss, a leaf of 'Iceberg' lettuce, and half of a 3-inch
pot cut longitudinally to provide shelter for the slugs during the day. A plexiglass cover with 1/2-inch holes (blocked with aluminum screen) provided air circulation. Cages were held in a fiberglass greenhouse.
Longevity and weatherability of molluscicides:
Deadline Bullets, Hacco Slug and Snail AG3.5, and RCO Slug and Snail Pellet Rain Resistant Formula provided consistently high mortality throughout the test period. Liquids baits such as Deadline 40, Deadline One Last Meal, and Corry's Liquid Slug and Snai l Control provided excellent control under wet conditions. Liquids are best suited as a barrier type treatment. However, poor coverage and the time and labor involved for application are factors which should be considered for commercial application.
Top Molluscicides Tested
% Mortality 1 day 7 days Deadline 40 (Liquid) 42 60 Deadline Bullets 55 40 Deadline Granules 54 15 Deadline One Last Meal (liquid) 13 55 RCO Slug & Snail Pellets 45 48 Hopkins Slug and Snail AG 3.5 58 47
Tests were conducted to evaluate the weatherability of the various molluscicides. Molluscicides were applied at the recommended label rate to 1-ft^2 cages consisting of a wood frame, aluminum screen bottom, and a plexiglass cover. Rainfall was simulated f or 5 min. daily (600 ml per cage) using overhead irrigation.
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Do not handle slugs with bare hands. Slugs and snails are known carriers of Angiostrongyliasis cantonensis, a nematode which may cause ensinophilic meningitis in humans and animals.
Each grower has unique conditions. Time of application and growing conditions (i.e., field vs. greenhouse culture) have a considerable influence on the efficacy and phytotoxicity of insecticides. Other factors including tank mixtures, temperat ure, and adjuvants also influence efficacy and phytotoxicity. Under such conditions, pesticides that were reported safe in this report may be phytotoxic.
We gratefully acknowledge DowElanco, FMC Corp., United Horticultural Supply, Valent USA Corp., GemChem Inc., Miles Inc., Meerkat Environmental Industries, and Agridyne Technologies for their support. This research was supported in part by the State of Haw aii, Governor's Agriculture Coordinating Committee, by the USDA, Cooperative State Research Service under a Floriculture Research Grant.
Trent Y. Hata,
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