PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Greenhouse whitefly (GHWF)
Scientific name
There are about 20 species of whiteflies in Australia
including the greenhouse whitefly (Trialeurodes
vaporariorum , Aleyrodidae,Order Hemiptera), also:
Ash whitefly (AWF) (Siphoninus phillyreae)
Eastern Australian native whitefly (Bemisia tabaci
Aus) (EANW)
Tobacco whitefly (TWF) (Bemesia tabaci)
Silverleaf whitefly (SLWF) (Bemesia tabaci B-
Biotype). Recently Bemesia tabaci Q-Biotype)
has been found in Australia which cannot be
differentiated visually from the Q-Biotype.
Spiralling whitefly (SPWF) (Aleurodicus dispersus)
AWF and SPWF are serious pests of plants in Australia.
www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7401.html
Host range
GHWF and SLWF have a broad and overlapping
host range of over 600 plant species. It is not
unusual to find both insects on the same property
or even on the same crop.
GHWF is a serious, persistent pest of broadleaved
plants in greenhouses and outdoors, eg
ornamentals, eg boronia, fuchsia, hibiscus; fruit,
eg citrus; vegetables, eg beans, cucurbits, potatoes,
tomatoes; weeds, eg sow thistle.
SLWF - many species, field crops, eg beans, carrots.
AWF - trees and shrubs, pome and stone fruit, citrus.
SPWF - fruits, vegetables, ornamentals, weeds.
Description & damage
Adults are small, delicate, moth-like, 1-2 mm
long with 2 pairs of white powdery wings which
are folded when at rest (Fig.116). Wings held
flat and roof-like over body. Adults are gregarious,
do not fly readily and usually remain on the undersurfaces
of young leaves uppermost on the host
plant. Males usually live for about 1 month and
females for 1-3 months. Adults fold their wings in
a triangle. Eggs are inserted vertically into the
leaf undersurface often in circles and are small,
bullet shaped and yellowish when laid and grayish
purple when mature. Nymphs are whitish to
greenish yellow, flattened and oval (scale-like)
with fine waxy marginal filaments (Fig. 115).
Nymphs are 0.3-0.75 mm long depending on
nymphal stage. Pupae have a few long hairs and a
fringe of very short hairs around upper edge.
Leaves. Nymphs and adults suck sap from new
shoots and leaf undersurfaces of soft-foliaged
plants. If an infested plant is disturbed, adults may
rise in the air, flutter about the plant but resettle
quickly. Leaves develop a sandy mottle. Nymphs
and adults secrete honeydew on which sooty
mould grows disfiguring plants and preventing
Table 33. Leaf symptoms caused by some sucking insects and mites.
photosynthesis. Parasitized nymphs are black and
commonly found on infested plants.
Heavily infested seedlings may die.
Fruit. Sooty mould may make fruit so dingy that
it has to be washed before marketing or eating.
General. Plants may wilt, turn yellow and
display reduced growth rates if infestations are
severe. The yield of established plants can be
reduced if infestations continue unchecked
throughout the growing season. Severe
infestations can cause plants to lose vigour and
wilt. Small numbers of whiteflies in a home garden
may not be a cause of concern, doing little damage.
Transmit virus diseases. GHWF spreads
lettuce infectious yellow virus which infects
petunia, zinnia and other hosts. SLWF spreads
tomato leaf curl virus in ornamentals and vegetables.
Diagnostics.
Do not confuse damage caused by thrips to
leaves with that caused by other insects and
twospotted mite (Table 33 below).
Adult whiteflies as a group, are easy to
distinguish from other insects, but it can be
difficult to distinguish one species from another.
Nymphs are often mistaken for scale insects
and are more difficult to identify but are
distinctive for each species (Fig 115).
Identification of one species from another is
based on size, shape of wings, pupae hairs,
pattern of egg laying, etc (Goodwin et al 2000).
GHWF - examine late instar or redeye pupal
stage with a hand lens (x10) or a microscope.
Some whiteflies only attack certain type of
plants, eg AWF mainly attacks trees and shrubs.
SLWF flies greater distances than GHWF.
Know which whiteflies are present in your crop so
you can select appropriate biocontrols/insecticides.
If unsure, consult a diagnostic service.
Lucid keys - www.lucidcentral.com/ Platanthera
Interactive Key to North America, north of Mexico
(Pupal Key to Genera of White Flies), also Whitefly
Fauna of the Word, Key to Cotton Insects
Greenhouse Silverleaf Ash Eggs
Spiralling
Fig. 115. Stationary later stage nymphs (pupae) of
different species of whiteflies (about 0.8 mm long). The pupal
stage which looks like small scale under leaves is often the
more distinctive if not send to a diagnostic service.
Upper leaf
surface
Lower leaf
surface
Greenhouse
whitefly
Sandy speckling,
Whiteflies,
Stationary nymphs,
honeydew, sooty mould
Various
leafhoppers
Speckled
feeding patterns
Clean, insects
have flown away
Lace bugs
Greenhouse
thrips
Twospotted
mite
Sandy speckling Silvering Sandy speckling
Lace bugs, spiny
nymphs, black
spots of excreta
Thrips visible,
black spots of
excreta
Mites visible,
webbing,
excreta
Insects and allied pests - Hemiptera (bugs, aphids, etc) 171