Transcript Greenhouse Pests - in blue

Greenhouse Pests
Insect & Mite Pests
David J. Shetlar, Ph.D.
The “BugDoc”
The Ohio State University,
OARDC & OSU Extension
Columbus, OH
© November, 2003, D.J. Shetlar, all rights reserved
Greenhouse & Interiorscape
Pest Management
Managing insect and mite pests in greenhouses
should be a simple task! If you believe in laws of
thermodynamics (i.e., matter can be neither created
nor destroyed), the biological corollary should be:
living organisms must come from living organisms!
In short, we know that pests can not spring forth
from “primordial much” which was a common
thought during the Dark Ages!
In short, if you start with a clean greenhouse and
clean plants, then pests should not be a problem!
Greenhouse & Interiorscape
Pest Management (cont’d)
The most common sources of insect and mite pests
in greenhouses are:
• Preinfested Stock (Cuttings and seedlings often
have pests when purchased. Start clean!)
• “Typhoid Mary” Plants (Stock that is infested and
isn’t removed before the next crop is begun. University
greenhouses are notorious for this! Smaller
greenhouse operations that grow a variety of crops
continuously are also guilty!)
• Fly-Ins (Greenhouse doors, cooling vents and air
vents are not properly covered allow flying insects to
enter)
Major Greenhouse Pests
•
•
•
•
•
•
Whiteflies
Mealybugs & Scales
Mites (spider mites, broad mites,
& etc.)
Thrips
Leafminers
Nuisance Pests (fungus
gnats, shore flies, & etc.)
Greenhouse Whiteflies
•
•
•
•
Greenhouse (Trialeurodes vaporariorum)
Sweetpotato (Bemisia tabaci)
Silverleaf (Bemisia argentifolii)
Bandedwinged (Trialeurodes abutilonea)
Best site on Internet: The Whitefly Knowledgebase
http://whiteflies.ifas.ufl.edu/
Typical group of greenhouse whiteflies – all stages
Notes: The greenhouse whitefly has been the traditional
whitefly found in greenhouses. In the mid 1980s, another
whitefly which was slightly smaller, slimmer and had a
more yellowish body became common in Florida and the
Carolinas. This new whitefly was a major problem on
certain greenhouse vegetables and flowers such as
poinsettias, gerbera daises, and hibiscus. This whitefly
was eventually identified as the sweetpotato whitefly –
Strain B, but this pest was subsequently described in
1994 as the silverleaf whitefly. At present, the
greenhouse and silverleaf whiteflies are the most
common pests in greenhouses, but the sweetpotato and
bandedwinged whiteflies are occasionally encountered.
It is important to identify each species since they have
varying susceptibilities to biological and chemical
controls.
Whitefly Life Cycles
Egg
Nymph I
(=crawler)
Nymph II
(=“scale”)
Nymph III
(=“scale”)
Nymph IV
(=“Pupa”)
Adult
At 70ºF, the greenhouse whitefly life cycle takes: 6-10 days
for egg hatch, 3-4 days as a nymph I, 4-5 days as nymph II,
4-5 days as nymph III, 6-10 days for the pupa. Adults can
live for 30 to 40 days.
Greenhouse whitefly pupa,
note raised upper surface and
long, glass-like spines.
Greenhouse whitefly
adults hold the wings
flatter over the body
and they are more
white in base color.
Greenhouse whiteflies:
note wings held wider and
more flat on body, and
pupae with long spines.
Silverleaf & sweetpotato
whiteflies: note wings
held closer to sides of
bodies, and pupae have
no spines.
Bandedwinged whitefly adults
Other whitefly species can be
found, especially in southern
greenhouses. Fortunately, most
are not significant problems in
production settings.
Palm whitefly adult and
“pupae.” Many whiteflies have
such characteristic waxy
fringes.
A giant whitefly and its
nymphs plus an old
pupal exoskeleton.
Whitefly Management
• Monitoring – visual inspection of plants, upper
leaves for adults, lower leaves for nymphs; yellow
sticky cards.
• Cultural Control – sanitation, resistant plants
• Biological Controls – parasitoids & diseases
• Chemical Controls – emphasis on insect growth
regulators, rotating chemistries, etc.
• Integrated Programs – combining cultural and
biological controls with chemical controls selected to
have minimum adverse action on biologicals.
Whitefly Monitoring
• Yellow sticky cards
• Visual Inspections – adults prefer to lay eggs on
younger foliage; undisturbed females lay eggs in
circles; various thresholds (e.g., whitefly nymphs
and/or pupae per leaf) have been developed for
certain crops.
Note rings of eggs
that indicate that the
females were
undisturbed for a
considerable time!
Whitefly Cultural Controls
• Start Clean! – start a crop with “clean” plant
material and keep rooms separated.
• Sanitation – keep weeds and other vegetation
surrounding greenhouses mowed, or eliminated with
herbicides or ground covers.
• Exclusion – screen vents, air cooling pads, etc.
with material with screens fine enough to exclued
white flies. Doors should be under positive air flow
(e.g., air flows out when opened).
• Use Resistant Plants – some cultivars appear to be
less able to support whitefly populations. Be sure to
ask seed dealers about resistant cultivars.
Whitefly Biological Controls
• Parasitoids – mainly Encarsia and Eretmocerus
species, many usage techniques (e.g., mainly
introductions or “banker” systems).
• Predators – green lacewings are often helpful in
field crops, lesser so in greenhouses.
See:
http://www.umass.edu/umext/floriculture/fact_sheets/pest_management/slwf.html
Encarsia formosa, a commonly used parasitoid. Parasitized
pupae turn black. Can you find the two adults?
Development Times for
Greenhouse Whitefly
Temp
(ºF)
Egg
Hatch
Nymphs
I-II-III
“Pupa”
(nymph IV)
Female
Preovi
85º
3
7
7
1
75º
6
8
7
1
70º
8
11
8
1
65º
11
17
12
2
60º
18
25
24
2
Scheduling Short Residual,
Contact Insecticides for Control of
Greenhouse Whitefly
(assuming “pupae” are resistant)
At 85º:
Eggs=3 Nymphs=7 Pupae=7 Adult Preovi=1
Day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
At 65ºF:
Eggs=11 Nymphs=17 Pupae=12 Adult Preovi=2
Day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
Whitefly Chemical Controls
• Soaps & Oils – best on foliage plants because of
phytotoxicity potential; kills mainly eggs, crawlers
and scale states by contact.
• Contact Insecticides – most pyrethroids kill by
contact and most have some residual action. Eggs
and “pupae” may be resistant, so reapplications may
be necessary to catch the crawlers or adults that may
emerge after an application.
• Systemic Insecticides – systemic insecticides are
usually effective for actively feeding stages of
whiteflies.
• Insect Growth Regulators – have been very
effective, especially as alternate chemistries.
Whitefly Chemical Controls
ALTERNATE CHEMICAL CONTROLS!
Whiteflies are notorious for developing resistance to
pesticides. Their high reproductive potential and
short generation time make them excellent at
developing resistance. While there is considerable
debate on resistance management, do not use the
same pesticide again if satisfactory control was not
achieved with a recent application. It is often
recommended that managers alternate chemical
groups on a regular basis if whiteflies need continual
control. Without cultural and biological controls,
chemical controls will eventually fail.
Greenhouse
Mealybugs & Scales
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Mealybugs (citrus, longtailed, Mexican, etc.)
Soft Scales (brown soft scale, hemispherical
scale, black scale, nigra scale, etc.)
Armored Scales (oleander, fern,
Boisduval, false Florida, cactus, etc.)
Sites on Internet:
http://www.ipm.uiuc.edu/greenhouse/insects/index.html
http://floriculture.osu.edu/archive/oct97/mealybug.html
Greenhouse Mealybugs
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Citrus (Planococcus citri)
Longtailed (Pseudococcus longispinus)
Mexican (Phenacoccus gossypii)
“Unnamed” (Phenacoccus madeirensis)
Root Mealybugs (Rhizoecus spp.)
Citrus mealybugs, early ovisacs,
and a couple of crawlers.
Longtailed mealybugs –
crawlers, nymphs, and
adults.
Phenacoccus madeirensis
All stages on chrysanthemum.
Ovisacs and crawlers.
A male.
Other mealybug species often
occur in lath-house
ornamentals in southern
states.
Striped mealybugs
Pink hibiscus
mealybugs being
tended to by fire
ants.
Mealybug Hosts
•
Citrus – 27 families of plants; begonia, coleus,
amaryllis, cyclamen, and dahlia are most commonly
attacked in greenhouses.
• Longtailed – 26 families of plants; Dracaenia &
ferns most commonly
• Mexican – mainly chrysanthemum, English ivy,
geranium, Gynura, hollyhock, Ixia, lantana, and
poinsettia.
• “Unnamed” – mainly chrysanthemum &
poinsettia as well as foliage plants.
• Root – numerous long-lived greenhouse plants but
most damaging to African violets.
Mealybug Life Cycles
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Citrus - males known but not obligatory; up to 600
eggs per ovisac; 10 days for egg hatch; 50-60 days per
cycle.
Longtailed - males obligatory; up to 200 eggs
per female, no ovisac, possibly live birth; two to three
months per cycle.
Mexican – males known; up to 400 eggs per
elongate ovisac; cycle can be completed in 47 days.
“Unnamed” – males known; up to 300 eggs
per elongate ovisac; cycle can be completed in 30 days.
Root – not much known; several species that lay
small numbers of eggs in compact ovisacs; slow
developing.
Greenhouse Soft Scales
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•
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Brown Soft Scale (Coccus hesperidum)
Hemispherical Scale (Saisseta
hemisphaerica)
Black Scale (Saissetia olea)
Nigra Scale (Parasaisetia nigra)
Brown soft scales – one on left has been parasitized
Hemispherical scales – all stages! Can you tell
which ones are parasitized?
Nigra scales
Soft Scale Life Cycles
•
•
•
•
Brown Soft Scale – ovoviviparous,
males uncommon; 60 days to mature.
Hemispherical Scale –
parthenogenic; up to 1000 eggs per adult; 40 to 105
days to mature.
Black Scale – parthenogenic
Nigra Scale – parthenogenic; lays eggs over
long period of time; 40 to 60 days to mature.
Greenhouse Armored Scales
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•
•
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Oleander (Ivy) Scale (Aspidiotus
nerii)
Cactus Scale (Diaspis echinocacti )
Fern Scale (Pinnaspis aspidistrae)
Bifasciculate Scale (Chrysomphalus
bifasciculatus)
•
Boisduval Scale (Diaspis boisduvalii)
Oleander scales are
irregularly round in shape.
Males are smaller and more
oval in shape.
Cactus scales are sexually
dimorphic, females being
rounded and males being
slender, elongate forms.
Fern scale females are
generally brown and
oystershell shaped. Males
are white with a medial ridge
running down the waxy
cover.
Boisduval females are irregularly rounded and
males are elongate, white and with a medial ridge
in the waxy covering. Settled nymphs produce a
patch of elongate waxy threads as they form
their covers.
Armored Scale Hosts
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Oleander Scale – numerous woody
plants
Cactus Scale – various cacti & orchids
Fern Scale – ferns and Aspidistra
Bifasciculate Scale – palms, rubber
plants, & figs
Boisduval Scale – palms, banana, cacti,
& orchids
Armored Scale Life Cycles
•
•
•
•
•
Oleander Scale – males & females
common; 90 eggs per female; 30-35 days to mature.
Cactus Scale
Fern Scale – males and females common;
few eggs per female; ~30 days to mature.
Bifasciculate Scale
Boisduval Scale – males & females
common; 200 eggs per female; 23 to 32 days to mature.
Mealybug & Scale Management
• Monitoring – early detection of mealybugs and
scales is important to achieve good control.
• Cultural Control – sanitation/start clean, throw
away severely infested plants!
• Biological Controls – parasitoid wasps are
common
• Chemical Controls – emphasis on systemics,
following spray schedules, etc.
• Integrated Programs – combining cultural and
biological controls with chemical controls selected to
have minimum adverse action on biologicals.
Greenhouse Mites
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•
Twospotted Spider Mite
(Tetranychus urticae)
Lewis Mite (Eotetranychus lewisi )
Southern Red Mite (Oligonychus
ilicus)
Broad Mite (Polyphagotarsonemus latus)
Cyclamen Mite (Phytonemus pallidus)
Bulb Mite (Rhizoglyphus echinopus)
Twospotted spider mites have typical spider mite life cycles. They have
egg, six-legged larval, eight-legged nymph I & II, and adult stages.
Between every molt, the mites settle down and don’t move for a day or
more, depending on the temperature.
Typical
twospotted
spider mite
population. The
eggs are
completely
spherical. Most
of these are
adults. The male
in the middle is
“guarding” a
female nymph II
that is in the
process of
molting into an
adult.
Larva (above); egg, nymph I & II
in molt rest, cast skins (right);
nymph II female and male
guarding (below).
When monitoring for spider
mites, the tell-tale stippling
is easily spotted. The mites
will be on the underside!
If left uncontrolled,
twospotted spider mites will
completely encase the foliage
in their fine silk. Note that the
mites use the webbing as a
walkway. Plants this heavily
infested should be thrown
away!
If left uncontrolled, spider mites can eventually kill their host plants.
When this is about to occur, the mites often cluster at the tops of the
plants in order to balloon to other plants. This is one such ballooning
cluster.
Remember that an unmated female that is blown to a new plant can start
an entire colony. When unmated, she can only produce eggs that will
develop into males. However, the female can live long enough to mate
with one of her sons and then she can begin to produce eggs that will
develop into females!
Development Times for
Twospotted Spider Mite
Temp
(ºF)
Egg
Larva +
Molt
Nymph I
+ molt
Nymph II
+ molt
Adult
Preovip
80.6
2.3
0.6
0.4
1.9
2.4
77.0
4.5
1.5
1.8
2.2
1.0
68.0
6.7
3.6
3.0
3.5
2.1
Longevity & Fecundity for
Twospotted Spider Mite
Temp
(ºF)
Development
Time (total)
Longevity
Ave Eggs
per Day
Oviposition
Period
Ave Total
Eggs
80.6
7.6
19.1
8.0
8.0
143.9
77.0
11.0
19.4
6.6
16.6
109.6
68.0
18.9
37.0
2.4
15.7
38.0
“Red Mites”
Greenhouse managers often talk
about “red mites” or “red spiders”
when they are referring to spider
mites. This is unfortunate, since
there is no such species such as a
“red mite”!
Twospotted spider mites
take on a red or orange
hue when chilled in fall
conditions (above)
Southern red mites and
European red mites have
conspicuous spines and a
reddish color (right).
Spider Mite Management
• Monitoring – early detection of spider mite
activity is important to achieve good control, look
for stippling.
• Cultural Control – start clean; remove weeds
surrounding greenhouse environment; regularly
syringe with water.
• Biological Controls – numerous predatory mites
are available and useful.
• Chemical Controls – soaps & oils work well by
contact; new miticides often have ovicidal activity,
etc.
• Integrated Programs – combining cultural and
biological controls with chemical controls.
Phalaenopsis Mite is a relatively
common mite pest of orchids. The
mites are very flat and reddish-orange
in color. Their feeding often causes
white pitting of the orchid surface.
Unless the orchid is rare, disposal is
the simple solution. Otherwise
repeated applications of soaps or oils
often work.
Cyclamen mites are small
mites that often concentrate
their feeding around leaf and
flower buds. This causes
stunting and distortion. Often
heavy infestations cause the
new leaves to die, making
them look like they have died
from Botrytus fungus.
The little white spot at
the end of the arrow is a
mature cyclamen mite!
Thrips in Greenhouses
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•
•
•
•
Flower Thrips (Frankliniella tritici)
Western Flower Thrips
(Frankliniella occidentalis)
Greenhouse Thrips (Heliothrips
haemorrhoidalis)
Banded Greenhouse Thrips
(Hercinothrips femoralis)
Gladiolus Thrips (Physothrips
simplex)
Notes:
The flower, greenhouse, and banded greenhouse thrips have been the
most common thrips, traditionally, in greenhouses. These thrips
cause damage to various greenhouse crops (floral, foliage and
vegetable). Their damage was usually noted to be foliar discoloration
(blanching of leaf tissues or streaking of flower petals) and damage to
floral parts necessary for seed production.
In the 1980s, the western flower thrips (WFT) increased in importance
when it was discovered that this thrips transmitted Tomato Spotted
Wilt Virus (TSWV). Subsequent to this discovery, WFT was also found
to be a vector of Impatiens Necrotic Spot Virus (INSV). Since these
viruses can infect a wide range of greenhouse plants and infected
plants can not be treated but have to be destroyed, considerable
research has been undertaken to develop more intensive management
programs for control of thrips.
The gladiolus thrips and some similar species are common pests of
greenhouse grown glads and other floral crops.
Thrips feed by rasping into
cells and removing their
contents. This causes
“blanching” of the feeding
area. Thrips also produce
small “tar spot” type of
excrement.
Adult thrips have
bladelike wings with a
long hair fringe.
Western flower thrips
nymphs feeding on leaf.
Note typical “blanched”
areas on leaf and tarspots.
Greenhouse thrips
adults are black, but
the nymphs are light
colored. Note the
greasy tarspots on this
leaf.
Thrips Life Cycles
(using gladiolus thrips)
egg
nymph I
nymph II
nymph III
nymph IV
“larva” 1
“larva” 2
“prepupa”
“pupa”
adult
Entomologists that work with thrips often call the first two nymphal instars
“larvae,” the non-active third instar nymph a “prepupa,” and the fourth
instar nymph a “pupa.”
Notes:
Most thrips have four nymphal instars, but the third and fourth instars do
not feed and are usually sluggish (= the third instar) or immobile (= the
fourth instar). Because of this inactivity during the process of transforming
from a non-winged nymph to the fully winged adults, many thrips experts
call these instars the “prepupa” and “pupal” stages, respectively.
Depending on the species of thrips, the “prepupae” and “pupae” usually
find protected places on host plants to undergo their molting processes, or
they may even drop from the plant and undergo these instars in the soil or
potting mixes.
Most thrips insert their eggs into plant tissues. Therefore, when managing
thrips, one has to keep in mind that the eggs, “prepupae,” and “pupae” are
usually in protected areas that will not be reached by pesticides. This
usually require adoption of spray schedules (e.g., spraying every few days
for a set period of time) in order to knock out hatching nymphs and newly
emerging adults.
Western Flower Thrips
First instar nymph (upper left),
second instar (above) and adult
(left).
Development Times for
Western Flower Thrips
•
•
•
Eggs – about 3 days at 80-85ºF
“Larvae” (1st & 2nd instar nymphs) – 3-4 days
“Prepupa” & “Pupa” (3rd & 4th instar nymphs) –
3-4 days
•
Adults – average 28 days longevity at 85ºF and
57 days at 68ºF
•
Fecundity – 125 to 250 eggs per female,
mating is not necessary.
Thrips in Greenhouses Diagnostics
•
•
Visual Inspection – look for
blanched areas and tiny tar spots
Sticky Cards – western flower
thrips shows a preference for blue sticky
cards, but yellow cards are fine for general
monitoring
Thrips Management in Greenhouses
• Monitoring – sticky cards are generally
recommended, early detection and number of
adults per card per day is used.
• Cultural Control – screening is available to
prohibit entry of thrips from outside; eliminate
surrounding vegetation.
• Biological Controls – several predatory mites
are available and useful.
• Chemical Controls – rotation of chemistry is
highly recommended as well as following strict
spray schedules.
• Integrated Programs – combining cultural and
biological controls with chemical controls.
Special Factors for Managing
Western Flower Thrips in
Greenhouses
In viral disease transmission, only the feeding nymphs (“larvae”)
can pick up the viral bodies from infected plants. The resulting
infected adults can then transmit the virus to other plants and
since they are highly mobile, spread of the virus can be very
rapid.
•
Exclusion – since infected thrips adults can come from
outside the greenhouse, special screens are commonly
installed in areas where this thrips can overwinter.
•
Plant Resistance – new cultivars of plants have been
developed that are resistant to the virus or the thrips. This
greatly reduces the risk of viral problems.
•
Sanitation – if one plant is discovered with virus, then the
entire crops is usually destroyed!
See:
http://floriculture.osu.edu/archive/oct00/thripsup.html
http://www.entm.purdue.edu/entomology/ext/targets/e-series/eseriespdf/e-110.pdf
Greenhouse Leafminers
•
•
•
•
•
“American Serpentine”
Leafminer (Liriomyza trifolii)
Serpentine Leafminer (Liriomyza
brassicae)
Vegetable Leafminer (Liriomyza
sativae)
Pea Leafminer (Liriomyza huidobrensis)
Chrysanthemum leafminer
(Chromatomyia syngenesiae)
Notes:
In the past, several types of leafminers (mainly dipterous and
lepidopterous) were occasional pests in greenhouse crops. In the late
1970s and early 1980s, dipterous leafminers in the Agromyzidae became
significant and wide spread pests of greenhouse floricultural and
vegetable crops.
At first, L. trifolii, was identified as the main pest and this was often
called the “chrysanthemum” leafminer because this was the crop most
affected. Soon, it was learned that a very similar fly, L. sativae, was also
involved. Both flies are yellow with black markings and you have to
closely inspect the head markings to differentiate between the two.
The vegetable and pea leafminers are significant pests of greenhouse
vegetable production.
These species have adult females that produce the typical “pin holes”
which are called “stings” in the greenhouse industry. These are places
where the female flies have punctured the leaf tissues to expose the
juices so that the fly can lap them up.
The larvae usually make winding mines that gradually widen as the
larvae mature.
Agromyzid leafminer adults
are about the size of a
common fruit fly. Most are
yellow with black markings,
but some can be almost
entirely black.
The serpentine, American
serpentine, and vegetable
leafminers are mainly yellow
with black markings like the
fly above.
The pea leafminer is
mainly black with some
yellow markings like the
fly to the right.
Serpentine leafminer
damage to a Schefflera
leaflets.
Extensive pinhole damage
to young Schefflera leaf. In
greenhouses, these spots
are commonly called
“stings” or “stipples.”
Greenhouse Dipterous Leafminer
Life Cycles
•
Complete Life Cycles – egg, larvae (three instars),
pupa and adult stages.
•
Overwinter as pupae in soil in southern states,
continuous activity in greenhouses.
•
Eggs – are inserted into leaf or petiole tissues, take
2-8 days to hatch.
•
•
Larvae – three instars take 12 to 20 days to mature.
Pupae – may be formed in mine or the last instar
larva can drop to the soil or potting mix.
•
Adults – females often live for 3 to 4 weeks, males
survive for shorter periods.
Leafminer Control in Greenhouses
• Monitoring – watch for pinholes and early signs
of mines.
• Cultural Control – screen to keep out adult flies;
eliminate surrounding vegetation.
• Biological Controls – several parasitoids are
useful.
• Chemical Controls – select systemic products
for larval control, though adults can be killed with
stomach poisons.
• Integrated Programs – combining cultural and
biological controls with chemical controls.
See:
http://www.gov.on.ca/OMAF/english/crops/facts/00-039.htm
Greenhouse Nuisance Pests
•
•
•
•
•
Fungus Gnats (several species of
Sciaridae, often Bradysia spp.)
Shore Fly (Scatella stagnalis)
Springtails
Millipedes & Isopods
Snails & Slugs
Fungus gnat adults have long
legs and antennae. They
often “dance” around on
leaves and flowers, rapidly
flying and running over the
surfaces. Adults cause no
damage.
Fungus gnat larvae are
nearly transparent, except
for the white fat bodies
visible through the
exoskeleton. They have
distinctive black head
capsules. The larvae may
feed on root hairs and
roots of plants.
Fungus Gnat Development Times –
Bradysia coprophila
Temperature
(F)
Larvae
(days)
Pupation
(days)
Survival
(out of 10 larvae)
65
15.40
17.80
16.7%
70
10.75
14.07
46.7%
75
10.50
14.10
93.3%
80
9.50
12.25
80.0%
Cultural Control of Fungus Gnat Populations –
an early study
Cultural Control of Fungus Gnat Populations –
an early study
Mix
Ave eggs/pot
Peat:Perlite:Soil
(1:1:1)
39.6 a
Terralite Metromix 350
(peat:vermiculite:bark:sand)
34.4 a
Bark:Sand:Soil
(1:1:1)
1.0 b
Terralite Metromix 350
with sand on top
1.6 b
Fungus Gnat Control in Greenhouses
• Monitoring – adults are easily monitored using
yellow sticky cards.
• Cultural Control – peat mixes seem to be very
attractive to adults; keep soil mix on dry side.
• Biological Controls – several parasitoids are
useful as well as insect parasitic nematodes.
• Chemical Controls – not normally needed but
some drenches are useful if populations become
excessive.
• Integrated Programs – combining cultural and
biological controls with chemical controls.
Fungus gnat (left) and shore fly (right) comparison.
Shore fly adults and larva feeding on blue-green
algae growing in a watering mat.
Notes:
Shore flies are about the size of fruit flies and they have the same features
– short antennae and legs. The larvae feed on blue-green algae and the
adults appear to feed on similar materials.
These flies become numerous where potting mixes are kept constantly
moist, especially where capillary mats are used (fiber mats that hold water
under greenhouse pots).
Neither the adults or larvae cause any plant problems, but the adults
produces numerous “fly specks” which are fecal and regurgitation spots.
These appear as tiny white to black, round spots on pots and plant foliage.
Probably the best way to manage these flies is to conserve water so that
blue-green algal growth is kept to a minimum.