|
|
|
|
 |
 |
|
|
|
|
Green-seeds.com:
flowers & ornamentals: articles
|
|
|
Horticulture Digest #106
MEALYBUGS AND SLUGS ON POTTED-FOLIAGE PLANTS
Hawaii's potted-foliage growers are concerned about shipment rejection
due to live insect pests. During the past year, growers have had problems
controlling the palm mealybug (Palmicultor palmarum), root mealybug (Rhizocus
hibisci), and two species of slugs--the brown slug (Vaginula plebeia)
and the two-striped slug (Veronicella cubensis).
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.
Results:
Foliar applied insecticides were very effective against the palm mealybug.
Dursban 50W and Talstar 8.0F resulted in 94 and 67% mortality, respectively.
Marathon 1G achieved only 17% mortality.
Experiment:
Three insecticides were evaluated for efficacy against the palm mealybug--Dursban
50W, 1.0 lb/l00 gal; Talstar 8.0F, 20 fl oz/100 gal; and the systemic
granular Marathon 1G, 1.3 g/6" dia. pot. Dursban and Talstar were applied
to the foliage twice at two-w eek interval. The spreader-sticker, Ad-here,
was added to both treatments at 6.0 fl oz per 100 gal. Marathon was applied
once by distributing it evenly on the media surface and watering it in
immediately after treatment.
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:
-
Inspect roots of newly purchased and slow growing plants by removing
the pot.
-
Avoid root-bound plants by repotting as needed.
-
Use clean pots and media.
-
Treat or remove alternate hosts outside of greenhouse.
-
Do not allow water from infested areas to drain into clean areas.
Crawlers can be transported in this way.
Chemical control of R. hibisci on Rhapis excelsa:
Results:
Unfortunately, we could
not achieve complete control with any chemical treatment. Dursban 50W and
Talstar 8.0F resulted in only 50 and 44% mortality, respectively. Removal
of pots before drenching increased efficacy of Dursban to 93%, but not Talstar.
Dif ferences in efficacy may be attributed to root density which may have
affected insecticide penetration. Phytotoxicity was not observed with any
of the treatments; however, caution should be taken when applying insecticide
drenches. Previous research has s hown watering plants prior to drench application
will significantly reduce phytotoxicity.
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.
Experiment:
Dursban 50W, Talstar
8.0F and Marathon 1G were evaluated for efficacy against R. hibisci. Dursban
and Talstar were applied as insecticide drenches by completely submerging
the root ball in 5-gal buckets containing 3 gal of insecticide solution
for 15 sec and gently agitating in an up and down motion 5 times. Controls
were submerged in water.
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.
CAUTION 
"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."
Hot-water Treatment of R. hibisci on Rhapis excelsa:
Results:
Hot-water treatment (46°, 46.5°, 47°, 47.5°, and 48°C)
shows great potential against R. hibisci. All temperature regimes tested
resulted in 100% mortality of R. hibisci.
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.
Experiment:
The potted part of the plant was submerged in a 250-gal commercial size
tank designed by Dr. Marcel Tsang, Agricultural Engineer at the College
of Agriculture, University of Hawaii at Hilo. Plants were held in the
49°C water until the internal temper ature of the root ball reached
a specified temperature. Five temperature regimes were tested against
the root mealybug, 46°, 46.5°, 47°, 47.5°, and 48°C.
Slug management strategy:
The
following suggestions may increase efficacy of slug control programs:
-
Monitor slug populations at night.
-
Locate the source of slugs. A barrier type of treatment may provide
satisfactory control once slugs are eliminated from the field.
-
Sanitation is very important in successful management of slugs. Slugs
feed on decaying organic matter and eliminating weeds and fallen leaves
removes their food source and breeding site.
-
Apply molluscicides after it rains. Slug baits don't last as long;
however, slugs are active after it rains.
-
A split application of slug baits is more effective than a single
heavy dose.
-
Liquid baits last longer than bullets and granules but has less coverage
and take longer to apply. They are best suited as a barrier type of
treatment.
-
Do not concentrate slug baits in one spot. This results in less coverage
and increases the chances of the bait being eaten by animals. Dogs,
horses, rodents, etc. will eat slug baits out of the open bag; therefore,
keep the bag out of reach.
-
Use molluscicides without attractants if pets are of concern.
-
Rodents (rats and mice) eat slug baits and seem to have a high tolerance
to metaldehyde. Therefore, if rodents are also a problem, eliminate
rodents first to increase your chances for successfully slug control.
Slugs
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:
-
bait molluscicides
-
molluscicide sprays
-
copper barriers and
-
slug traps
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:
Results:
Efficacy (% mortality) of molluscicides against the brown slug were as
follows:
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%
Experiment:
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:
Results:
Slug baits were more
effective after they were moistened; however, efficacy greatly diminished
thereafter. Because granules give better coverage than bullet and liquid
formulations, initial kill was high. Unfortunately, because of their size,
granules do not last very long.
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
Experiment:
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.
CAUTION
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.
DISCLAIMER
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.
When
using unfamiliar insecticides, the grower should first test the pesticide
on a small group of plants before treating the entire crop and continuously
check plants (leaves, roots, flowers, active growing points, etc.) for
phytotoxicity 4-6 weeks after insecticide application. Systemic insecticides
can damage growing tissue and injury may not be visible until new leaves
or flowers have emerged. Plants injured by systemic insecticides may
never recover or take longer to recover than plants injured from contact
insecticides.
Use
pesticides safely. Follow the manufacturer's instructions on the use
and application as well as storage and disposal. This publication is
for educational purposes only. Consult your Cooperative Extension Service
or the Hawaii Department of Agriculture for authorized special need
(SLN) registrations or additional information.
Acknowledgments
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,
Benjamin K. S. Hu, and
Arnold H. Hara, arnold@hawaii.edu
Department of Entomology, CTAHR
University of Hawaii at Manoa
|
|
|
|
|
|
|
|
|
|
|
Green - Seeds Co., Ltd.
81/10B Ho Van Hue Street, Phu Nhuan District, Ward 9, Ho Chi Minh City, Vietnam
Tel: +84 (8) 847 6901 - Fax: +84 (8) 844 1392 - Email: info@green-seeds.com
|
|
|
