SHEET405 - CUCUMBER

Greenhouse Cucumbers:
Guidelines for Biological Control
Biological controls have been used in commercial greenhouse cucumber production in
Canada since the early 1980’s. Biological control is most effective when used in an
Integrated Pest Management (IPM) program (see Sheet 160). As in any IPM program,
success depends upon correct identification of pest problems, regular monitoring,
careful timing and integration of complementary control measures. It also depends on
good clean-up, sanitation and other measures that remove breeding sites for pests and
prevent them from entering the greenhouse.

The primary pests in greenhouse cucumbers are fungus gnats (Bradysia spp.), western
flower thrips (Frankliniella occidentalis), greenhouse whitefly (Trialeurodes vaporariorum)
and two-spotted mites (Tetranychus urticae). Melon aphid (Aphis gossypii) can be a serious
problem in some situations, while other species of aphids, caterpillars and Lygus bugs
may also occur.

Challenges for using biological controls successfully on cucumbers are:

• Controlling pests during winter months. When the natural daylength is short it
induces many biological controls to go into diapause.
• Lack of pollen in cucumber crop flowers. This means there is no alternative food
source for biological controls, making them more difficult to establish.
• Chemicals used to control plant diseases. Fungicides to control Pythium root rot and
powdery mildew can interfere with development of biological controls.

The following guidelines contain practical tips for achieving good results against pests
in greenhouse cucumbers. Recommended release rates for each biological control are
shown in Table 1. More detailed information on pests and biological controls can be
found in the separate information sheets for each species.

Start Right with Cucumber Seedlings

IPM for cucumber begins with seedling production. It is important that propagators
establish the fungus gnat predator, ‘Hypoaspis’ (see Sheet 230) at the seedling stage.
Propagators must also supply information about all pesticides that have been used on
seedlings. This is important to know as some pesticides can interfere with the later use
of biological controls.

If powdery mildew is a chronic problem, consider choosing a mildew tolerant cultivar to

reduce the need for fungicide applications that can interfere with biological control.

General Monitoring
There are two main ways to monitor for common cucumber pests:
• Trapping pests on yellow sticky cards. These are used to monitor for whitefly, thrips
and fungus gnats. Blue traps are also used for thrips but yellow traps are usually
preferred because they can be used for whitefly as well. Inspect traps weekly; replace
every 3-4 weeks as glue becomes less effective. Place traps at the top of the plant
SHEET405 - CUCUMBER

canopy for whiteflies and thrips; place them about 25 cm (1 foot) above the growing
media for fungus gnats.
• Visual inspection of plant leaves. This should be done weekly for signs of two-
spotted mites, aphid infestations and other problems.

WHITEFLIES
The main pest in greenhouse cucumbers is the greenhouse whitefly (for more on
whiteflies, see Sheet 310). Whiteflies damage greenhouse cucumbers by covering fruit
and leaves with the sticky honeydew as they feed. High whitefly populations also
reduce the vigour of plants. Whiteflies can be controlled by the parasitic wasp,
‘Encarsia’, and the predatory beetle, ‘Delphastus’, by following steps described below.

Monitoring Tips
• Begin in the empty greenhouse, before seedlings are planted out.
• Hang up yellow sticky cards or tapes at the rate of 1 trap/50-100 m² (500-1000 ft²).
• Check traps weekly for adult whiteflies.

Release Biological Controls

Both biological controls for whiteflies described below can be used together.

Encarsia: Encarsia formosa is a tiny, 1 mm (1/20 inch) long, wasp that parasitizes
immature stages of whitefly. It is sold as loose parasitized scales or scales glued to cards,
from which the adult wasps emerge. As the wasp develops inside, greenhouse whitefly
scales gradually turn black; parasitized sweet potato whitefly scales turn a tan colour.

If there is a history of whitefly problems best results are achieved when Encarsia are
introduced preventively, at low rates, before whiteflies are found on monitoring traps.
Releases continue, usually weekly and are maintained until 80% of whitefly pupae
appear parasitized. (For more on Encarsia, see Sheet 210).

In warm regions or areas where a large number of greenhouses have whitefly

infestations, the whiteflies may move onto outdoor plants. This makes them more
difficult to control as whiteflies continually re-infest the crop plants. Encarsia are less
effective during cool weather and overcast periods, therefore whitefly populations must
be monitored closely.

Delphastus: Delphastus catalinae is a small, black, 1.4 mm (1/15 inch) long, lady beetle.
Both adults and larvae feed on whitefly eggs and immature stages. Delphastus is sold
as adults and should be applied as soon as whitefly are detected. Delphastus works
well with Encarsia because it avoids feeding on parasitized whitefly scale (for more on
Delphastus, see Sheet 244).

Other Measures
• It is essential to start with a clean crop at the beginning of the season, therefore
destroy all crop residues and dispose of them at a site remote from the greenhouse
SHEET405 - CUCUMBER

• If the previous crop was infested with whiteflies, leave the greenhouse entirely
empty of plants for 5 days, with heat, to starve whiteflies; or, kill them with cold by
allowing the greenhouse to freeze below -10C for a week.
• If a plant-free period is not possible between crops, use a short-residual fumigant
such as naled (Dibrom©). Apply at the end of the crop, before removing plant debris,
and again to the empty greenhouse. Sprays such as bleach and Virkon used for
disease control will not kill whitefly. Add insecticidal soap or dormant oil to the
spray used to wash down the greenhouse structure and floor between crops to kill
whitefly and other pests that often move to the walls or ceiling or hide in protected
areas.
• Keep the greenhouse weed-free, and maintain a 3-m (10-ft) wide, weed-free border
around the greenhouse.
• Do not keep ornamental plants in a cucumber greenhouse as these are also whitefly
hosts.
• If greenhouse whitefly numbers are high, hang yellow sticky tapes (up to 1 tape per
plant) at the top of the plant canopy to trap adult whiteflies. If sweet potato whitefly
is present, hang traps about 1 meter below the top of the plants.
• If whiteflies are present on outdoor plants, screen all entry points.

FUNGUS GNATS
Fungus gnats can cause significant damage in soil-less or sawdust bag cultures. In
cucumbers, most damage is caused by the larvae feeding on tender roots and on the
lower part of the stems. As root area is lost, cucumber plants become more susceptible to
drought stress and root rot infections. Adult fungus gnats can also transmit root rot and
other diseases. If the humidity in the greenhouse is very high, fungus gnat larvae may
feed on and destroy the growing points of the cucumber laterals. (For more on fungus
gnats, see Sheet 320).

Monitoring Tips
• Use yellow sticky cards at a rate of 1 trap/500 m² (5,000 ft²).
• Place cards about 25 cm (1 foot) above the soil or rockwool surface.
• Check traps weekly and record the number of adult fungus gnats; replace traps
every 3-4 weeks as the glue dries out.

Identify
It is important to distinguish between fungus gnats and shore flies because biological
controls for fungus gnats do not work on shore flies (for descriptions, see Sheet 310).

Release Biological Controls

The following three species of biological controls are compatible with each other and can
be used together.

‘Hypoaspis’: This soil-dwelling predatory mite feeds on fungus gnat larvae. The best
way to use Hypoaspis is to establish it in the greenhouse before fungus gnats appear.
Apply to cucumber seedlings in flats or cubes at the start of the growing season, and
then again when planting out. By feeding on other soil organisms, Hypoaspis
SHEET405 - CUCUMBER

populations can build up to high numbers that are effective in keep fungus gnat
populations low. (For more on Hypoaspis, see Sheet 230).

Supplement Hypoaspis with other biocontrols (below) if fungus gnat populations are
high.

Insect Parasitic Nematodes: Steinernema carpocapsae, S. feltiae, and Heterorhabditis spp. are
beneficial nematodes sold to control fungus gnats and other insects. They can be applied
to the soil through conventional sprayers or through the irrigation system. Nematodes are
effective against high populations of fungus gnats but, unlike Hypoaspis, will not
reproduce or remain in the growing media and must be reapplied.
• Apply nematodes when yellow sticky traps average over 50-75 fungus gnat adults
per trap, weekly, or while fungus gnat populations appear to be increasing.
• If root diseases are a problem in the crop, apply nematodes sooner to reduce the risk
of disease transmission by fungus gnat larvae.
• Three applications, 7-10 days apart, are usually required. Nematode products vary,
so follow product recommendations for rates. Calculate application on the actual
growing area, not the greenhouse area.

Note: The actual growing area for rockwool cultures with plant densities of 1.2-1.4
plants/m2 (10 ft²), is typically 1/3 to 1/4 of the total floor space.

Bacillus thuringiensis israelensis (BTI): A strain of this bacteria that infects fungus gnat
larvae is available (Vectobac®). It is applied in water to the soil or growing media after
fungus gnats are established (follow instructions on the product label).

Other Measures
• It is essential to eliminate wet spots in the greenhouse where fungus gnats can breed
by improving drainage, repairing leaks in plumbing, adjusting automatic irrigation
equipment, etc.
• Control is usually better in greenhouses with white plastic floors because fewer
breeding sites are available for fungus gnats.
• Control fungus gnats in other crops in adjacent greenhouses.

WESTERN FLOWER THRIPS (WFT) & ONION THRIPS

Western flower thrips is more likely to be a problem in greenhouses with ornamental
plants on site. Thrips damage leaves and distort the fruit of English cucumbers by
feeding and laying eggs in leaf and flower tissues and young developing fruit. When
WFT populations are high the adults are found in high numbers in the cucumber
flowers. Onion thrips will also attack cucumbers but the damage is usually confined to
older leaves and is less severe. Adult onion thrips are not as attracted to cucumber
flowers and fruit as WFT are (for more on thrips, see Sheet 320).

Monitoring Tips
• Use yellow or blue sticky cards (using the same yellow cards for whitefly monitoring
saves time) at a rate of 1 trap/50-100 m² (500-1000 ft²). Place traps at the top of plant
canopy.
SHEET405 - CUCUMBER

• Count the number of thrips on traps weekly; replace traps every 3-4 weeks as the
glue dries out.
• Examine a minimum of 20 leaves from mid-plant level in each infested area. Look
for presence or absence of both thrips and Cucumeris predatory mites. When each
leaf with thrips also has predators present, it is an indicator that the thrips
population should begin to decline.

Release Biological Controls

The following three species of biological controls are compatible and can be used
together.

‘Hypoaspis’: This soil-dwelling predatory mite feeds on the immature stages of thrips in
the soil or growing media. Hypoaspis alone cannot control thrips infestations, but it
contributes to the effectiveness of biological control when used with other predators (for
more on Hypoaspis, see Sheet 230).

‘Cucumeris’: The predatory mite Amblyseius cucumeris feeds on immature stages of

thrips. It is available in slow release bags, which are placed among plants as soon as
plants begin to climb the trellis wire. Cucumeris is also available in a loose bran carrier,
which is sprinkled onto leaves. Releases should continue until there is a 1:1 ratio of
thrips to Cucumeris on leaves as determined by monitoring (see monitoring above)(for
more on Cucumeris, see Sheet 220.

It usually takes 4-6 weeks to see a drop in the number of thrips caught on traps as a
result of releasing Cucumeris.

‘Orius’: The tiny pirate bug (Orius spp.), is attracted to cucumber flowers and feeds on
all stages of thrips. Orius are only effective from March to September because they do
not reproduce if daylength is less than 16 hours. Orius should be released once thrips
are established, on plants where thrips numbers are the highest in the greenhouse.
Release at least 500 Orius at one time to establish a breeding population (for more on
Orius, see Sheet 222).

Other Measures
• Avoid thrips infestations by thoroughly cleaning up the crop at the end of the
season. Treat the greenhouse with naled (Dibrom®) after the last pick, before
removing cucumber plants, and again after the greenhouse is empty.
• To starve thrips between crops, maintain a heated greenhouse, empty of plants,
which forces adult thrips to emerge from the soil-borne pupal stages.
• If thrips populations were high in the preceding crop, it may be advisable to apply
lime to the ground before covering the greenhouse floor with plastic. Care should be
taken to overlap and tape, or glue, the floor covering together.
• Do not maintain any ornamental plants in the greenhouse, and maintain a weed-free
border, 3-m (10-ft) wide, around the outside perimeter of the greenhouse.

TWO-SPOTTED MITES (TSM)

Two-spotted mites are common, important pests of greenhouse cucumbers (for more on
two-spotted mite, see Sheet 300). During warm weather, TSM populations reproduce
very quickly and cause economic damage to cucumber plants.

Controls should be applied at the first sign of TSM infestation, even if the infestation is
minimal.

Monitoring Tips
• Inspect leaves under 10-15 X magnification for TSM infestation.
• Some growers use bean seedlings or climbing runner beans as trap plants to detect
the first appearance of TSM on new crops. TSM damage is easy to see on bean
leaves, which alerts growers that there may be mites on cucumber plants.

Release Biological Controls

TSM can reproduce very rapidly on greenhouse cucumber so it is important to apply
biological control agents as soon as mite damage is detected. A combined attack using
the three biological controls listed below will provide the best results.

‘Persimilis’: The predatory mite, Phytoseiulus persimilis, is a very effective control for
TSM in cucumbers. The predators develop twice as fast as the pest at moderate
greenhouse temperatures (for more on Persimilis, see Sheet 200).
• When TSM are first seen, introduce Persimilis onto all infested leaves using at least
2000-3000 Persimilis per introduction. If treating a “hot spot”, where TSM numbers
are high, plan to continue releases until predator mites are present on all infested
leaves.
• Use the Persimilis shipped on bean leaves, rather than vermiculite, because
predators survive shipping in better condition and are easier to apply. Place bean
leaves with Persimilis on cucumber leaves near TSM infestations or on the growing
points of plants. Alternatively, apply the ‘HOT SPOT’ Persimilis product (which
contains high numbers of Persimilis in vermiculite) to each infested site.
• Once Persimilis are established, thousands will be produced on each cucumber leaf.
To speed distribution, pick some of these Persimilis “nursery” leaves and move them
to other plants all around the infested sites and throughout the crop.
• If TSM populations are high (i.e., there are large numbers of mites clustered on webs,
stringing or dropping down from the plants), spray once or twice with fenbutatin
oxide (Vendex®), then release Persimilis when the last spray has dried. Vendex does
not kill the egg stage of the spider mites and will not harm predatory mites.

‘Stethorus’: The tiny, black lady beetle, Stethorus punctillum, is effective at controlling
TSM populations and can be used with other biocontrol agents. Stethorus is active over a
wide temperature and humidity range, feeds on all stages of TSM and adult beetles fly
and are good at finding small colonies of TSM. Stethorus adults are available from
suppliers. They should be released in infested sites as soon as TSM are detected (for more
on Stethorus, see Sheet 207).

‘Feltiella’: The predatory midge, Feltiella acarisuga, may also be used to control TSM on
cucumber. Feltiella larvae feeds on all stages of TSM. Feltiella do best when humidity is
over 50%RH and at high mite densities. They should be released early in the season once
TSM becomes established (for more on Feltiella, see Sheet 280).

Other Measures
• Chemical control in conjunction with biological control is recommended if mites are
clustering in balls or “stringing” down from the plant or detected in high numbers
without predators present. Fenbutatin oxide (Vendex®) is safe for use with
Persimilis, but check compatibility list (Sheet 180) before using other pesticides with
biological controls.
• Once Persimilis has been released, maintain warm temperatures (optimum 25oC) and
high humidity (optimum 80-90% RH) to encourage the predators. Mist the crop if
necessary.
• It is important to finish each crop with low populations of TSM. High numbers at the
end of the year result in the survival of many red colored diapausing (overwintering
stage) spider mites that will re-infest the next crop early in the season. If mites are
still a problem in late July, a miticide such as Avid should be applied in August to
prevent diapausing mites from over-wintering. Pesticides are less effective against
the diapausing form of TSM present in the fall.

APHIDS
Aphids (such as the melon aphid, Aphis gossypii) can be a serious problem in greenhouse
cucumbers. New infestations are usually detected first on cucumber leaves and stems.
The melon aphid reproduces very rapidly on cucumber and all three biological control
agents listed below should be released as soon as possible.
• Release ‘Aphidius’ parasitic wasp (Aphidius matricariae) (see Sheet 242) to parasitize
the melon aphid.
• Release ‘Aphidoletes’ aphid midges (Aphidoletes aphidimyza) (see Sheet 240) between
March 15 and August 15, at a high rate, weekly, until aphids are controlled.
• Release the lady beetle, Harmonia axyridis, to control all species of aphids. If the aphid
infestation is widespread, also release field-collected Hippodamia convergens as well
(for more on both lady beetles, see Sheet 244).

CATERPILLARS (CABBAGE LOOPERS, ETC.)

The caterpillars of several species of moths and butterflies may become serious pests in
if their numbers are allowed to build up and should not be ignored.
• Hand pick and destroy any larvae found on young plants; use an ultraviolet (UV)
light trap to catch adult moths (for instructions on making a light trap, see Sheet
500).
• If intake fans are used, screen with 5 mm (¼ inch) mesh screen. This will also stop
Lygus and other flying pests.

Release Biological Controls

• Spray Bacillus thuringiensis (Dipel® or Foray®) at label rates every 3 days, for several
weeks, as soon as caterpillars are first detected. Ensure good coverage of both upper
and lower leaf surfaces.
• Trichogramma spp. parasitic wasps (see Sheet 270) attack moth eggs and can assist in
control. Apply weekly for at least 4 weeks or until looper populations are controlled.
• Predatory bugs, such as ‘Podisus’ (see Sheet 280) and ‘Orius’ (see Sheet 222) attack
eggs and small stages of caterpillar larvae.
• The parasitic wasp ‘Cotesia’ (see Sheet 280) attacks caterpillars and may be available
for release.

LYGUS BUGS
Several species of Lygus bugs attack cucumber plants. Their toxic feeding causes
abortion or death of the affected growing point.
• Hand pick and destroy any adults or larvae found on the plants.
• Screen intake vents and other large openings with 5 mm (¼ inch) mesh screen.

Summary of IPM Guidelines Greenhouse Cucumbers

Between crops:
• Treat with naled (Dibrom®) after last picking; wash greenhouse structure.
• Remove crop debris, heat empty greenhouse for 3-5 days.
• Cover floors with white plastic.
• Improve drainage to eliminate wet spots.
• Remove all weeds inside and around greenhouse perimeter.
• Screen vents where caterpillars or Lygus bugs are problems.
At start of crop:
• Whitefly: Release Encarsia at low rates.
• Fungus gnats and thrips: Introduce Hypoaspis at the start of the crop.
When pests are detected:
• Fungus gnats: Apply insect parasitic nematodes, BTI.
• Whitefly: Release Encarsia until 80% of whitefly pupae are parasitized; release
Delphastus.
• Two-spotted mites: Apply Persimilis, Stethorus, Feltiella as needed.
• Western flower thrips: Apply Cucumeris as needed; add Orius if thrips numbers
high.
• Aphids: Release Aphidius, Aphidoletes and, if aphid numbers are high, Harmonia
and Hippodamia lady beetles.
• Caterpillars: Spray BT, release Trichogramma, use UV light traps for adults
• Lygus: Hand-pick all stages.