PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Gladiolus thrips
Scientific name
Thrips simplex (Thysanoptera). A key pest in Qld,
SA, a minor pest in NSW and NT. An entire crop
can be ruined if control is inadequate.
Host range
Ornamentals: Unlike many other species of
thrips, gladiolus thrips is restricted in its host
range. A major pest of gladiolus, minor pest of
carnations, iris, calla or arum lily, torch lily or 'redhot
poker' (Kniphofia sp.), montbretias (Tritonia
spp.), and tiger flower (Tigridia pavonia).
Description & damage
Leaves, flowers and corms may be damaged by
nymphs and adults rasping the surface of plant
tissues and sucking up the sap which exudes.
Adult females, are about 2 mm long, dark
brown with 2 pairs of delicately fringed wings.
Males are slightly smaller than females. Nymphs
are similar to adults but are pale yellow and
wingless. Pre-pupae and pupae are yellowish.
Damage.
Leaves. Young nymphs feed inside leaf
sheaths and buds. Adults mostly feed in the
open on leaves which become bleached and
silvery. Extensive leaf damage may cause new
corms to be stunted.
Flowers. Thrips move into flower spikes as
they develop. Flower spikes may be stunted,
flowers may fail to open or be distorted or the
petals marked with small pale flecks. Injury is
often wrongly attributed to drought or disease.
Slight injury especially on dark blooms appears
as whitish or flecked areas, even a few flecks
reduces their market value. Damage is very
noticeable on dark-colored flowers.
Corms. Thrips also feed and breed on corms in
the ground and in storage. Surface of corms
becomes sticky, then hard and scabby. Young
root buds may also be injured. When damaged
corms are planted, thrips feed on young roots
and growth from the corm may be seriously
affected.
Diagnostics. Damage to leaves and flowers
may be confused with damage caused by mites,
drought, etc.
It can be difficult to distinguish one species from
another. Seek specialist advice if necessary.
Home gardeners need to identify the problem
only as thrips.
Commercial growers need to identify the
species of thrips, eg gladiolus thrips, western
flower thrips (WFT) (page 138).
Various keys are available, eg Lucidcentral:
Search for a Thrips ID key www.lucidcentral.com/
Pest cycle
There is a gradual metamorphosis (egg,
nymph (2 stages), pre-pupa, pupa and adult) with
many generations during the warmer months of the
year. The life cycle from egg to adult varies from
about 10 days in warm weather to a month or
more under cool conditions. The tiny eggs are
deposited in plant tissue. Nymphs and pre-pupae
are found within leaf sheaths and flower buds, but
the adults feed mainly in the open on the leaves.
The pupal stage may be passed either on plants or
in the soil beneath plants.
‘Overwintering’
In coastal areas all stages of the life cycle have
been observed during winter. If plants are left for a
long time in the field after flowering, thrips will
migrate to, and ‘overwinter’ in, the corms as the
leaves die down and continue feeding.
Spread
Adult thrips do not fly readily, migration through
a gladiolus crop is slow, but is assisted by wind.
By the movement of infested corms.
Conditions favouring
Hot dry conditions. Cool, wet weather affects
them adversely and heavy rain at times destroys
large numbers. Gladiolus thrips can cause serious
damage to late flowering plants and stored
gladiolus corms.
Egg, 1 st and 2 nd stage nymphs Pre-pupa and pupa Adult thrips Natural size
Fig. 97. Gladiolus thrips (Taeniothrips simplex). Photo NSW Dept of Industry and Investment.
Insects and allied pests - Thysanoptera (Thrips)
133