SHEET 410- TOMATO
Greenhouse Tomatoes:
Guidelines for Biological Control
Biological controls are widely used in commercial greenhouse tomatoes in North
America. As growers shift from using chemicals to using biological controls for pests,
conditions have become favourable for using bumble bees for pollination. Biological
control are 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 of greenhouse tomatoes grown in rockwool or hydroponic systems
are greenhouse whiteflies (Trialeurodes vaporariorum), fungus gnats (Bradysia spp.) and
two-spotted mites (Tetranychus urticae). Where ornamental crops are grown nearby, or
were grown in the preceding crop, sweet potato whitefly (Bemesia tabaci) and western
flower thrips (Frankliniella occidentalis) may be a problem; the latter is more likely to
occur in soil cultures. Aphids can be an occasional problem.
Most biological controls are used after the target pest is found to be present, but some
can be established ahead of time. The two main ways to use biological controls in
tomatoes are:
• early, inoculative releases to establish them before pests are detected.
• inundative releases, after monitoring shows that the target pests are present. Start
with early releases as much as possible because this increases the chance of achieving
successful control. This is especially important on tomatoes, because the toxic, glandular
hairs on leaves and stems hinder the movement of some biological controls.
The following guidelines contain practical tips for achieving good results against pests
in greenhouse tomatoes. 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.
General Monitoring
There are two main ways to monitor for common tomato pests:
• Trapping pests on yellow sticky cards or ribbons. 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 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 (using 10-15X magnifying
lens) weekly, for signs of two-spotted mites, aphid infestations and other problems.
SHEET 410- TOMATO
WHITEFLIES
The main pest in greenhouse tomatoes is the greenhouse whitefly (for more on
whiteflies, see Sheet 310). Sweet potato whitefly is occasionally a problem, but usually
only in tomatoes grown near ornamentals, such as poinsettias. Whiteflies damage
greenhouse tomatoes by covering fruit and leaves with the sticky honeydew as they
feed. High populations also reduce the vigour of plants. The sweet potato whitefly can
cause a net-vein symptom in fruit. Both species of whiteflies can be controlled on tomato
by the parasitic wasp, ‘Encarsia’, 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/200 m² (2,000 ft²).
• Check traps weekly for adult whiteflies.
• Early in the season under low light levels whitefly may remain on the plant and not
be detected on traps. Examine the underside of leaves on about 1% of the plants.
• Use the leaf or trap counts to determine rates of introduction of Encarsia and other
biological controls.
Identify Whiteflies
Correct identification is important because treatment recommendations differ for each
species. It is difficult to identify whiteflies trapped on sticky cards, therefore it is
advisable to examine adults and immature whiteflies on leaves (for descriptions, see
Sheet 310).
Release Biological Controls
‘Encarsia’: Encarsia formosa is a tiny, 1 mm (1/20 inch) long, wasp that parasitizes
immature stages of whitefly. It is sold as parasitized 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.
Best results are achieved when Encarsia are introduced 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).
‘Dicyphus’: The predatory bug Dicyphus hesperus is a new and experimental addition to
the list of commercial biological controls (for more on Dicyphus, see Sheet 280). It is best
used along with other biological controls in greenhouse crops that have—or because of
past history, are expected to have—whitefly, spider mite, or thrips problems.
• Dicyphus needs large numbers of prey so releases them only in areas where pests
have been detected.
• Release Dicyphus as soon as whiteflies are established, early in the season, and again
in 2-3 weeks.
• These predators also feed on plants, but damage on tomato is slight unless
population levels exceed 100 Dicyphus/plant.
SHEET 410- TOMATO
Other Measures
• It is essential to start with a clean crop at the beginning of the season, therefore
destroy all crop residues.
• 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 for a week (must be below -10 C to kill adults)
• 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.
• 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 tomato 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 m (3 ft) below the top of the plants.
FUNGUS GNATS
Fungus gnats can cause significant damage in soil-less cultures. In tomatoes, most
damage is caused by the larvae feeding on tender roots. As root area is lost, tomato
plants become more susceptible to drought stress and less tolerant of root infections.
Adult fungus gnats can transmit root rot and other diseases (for more on fungus gnats,
see Sheet 320).
Monitoring Tips
• Use yellow sticky cards at a rate of 1 trap/500-1,000 m² (5,000-10,000 ft²).
• Place cards about 25 cm (1 ft) above the soil or rockwool surface.
• Check traps weekly for 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 and may 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 tomato 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 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.
SHEET 410- TOMATO
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. They are
effective against high populations of fungus gnats.
• Apply nematodes when yellow sticky traps average over 50-75 fungus gnat adults
per trap, weekly, or while fungus gnat populations are 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 always follow product recommendations for rates.
Note: The actual growing area for rockwool cultures with plant densities of 2-3
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, 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.
TWO-SPOTTED MITES (TSM)
Two-spotted mites are increasingly important pests of greenhouse tomatoes. They are
difficult to control with biological controls or with chemicals (for more on two-spotted
mite and the carmine mite, see Sheet 300). Strains of TSM adapted to tomatoes survive
well despite the toxic, glandular hairs on tomato leaves and stems, and strains such as
the carmine mite can cause severe damage.
Controls should be used at the first sign of TSM infestation, even if it is minimal. An
early sign of a TSM infestation is speckled leaves. Later, infested tomato plants become
yellowish, stressed and may develop only 3-4 flowers per truss.
Monitoring Tips
• Inspect leaves under 10-15 X magnification for TSM infestation.
• Some growers use climbing bean plants (var. Scarlet Runner) as trap plants trained
up support posts to detect the first appearance of TSM in tomato greenhouses. TSM
damage is easy to see on beans, which alerts growers that there may be mites on
tomato plants as well as acts as a nursery plant for the production of predators.
Release Biological Controls
‘Persimilis’: The predatory mite, Phytoseiulus persimilis, can be used to control TSM in
tomatoes. The predators develop twice as fast as the pest at moderate greenhouse
temperatures. Unfortunately, biological control using Persimilis is not as reliable on
SHEET 410- TOMATO
tomato as in other crops because:
• Predatory mites have difficulty moving on tomato plants because they are caught in
the glandular hairs on the stems.
• Spider mites on tomatoes are not easy to see, so populations may be quite high
before they are detected.
For best results:
• When TSM are first seen, spray affected plants (usually only the top 1/4 of the
plants) with fenbutatin oxide (Vendex®).
• Introduce Persimilis one week later (for more on Persimilis, see Sheet 200).
• Use the Persimilis shipped on bean leaves. This gives better results on tomato than
the vermiculite product, which is difficult to apply to tomato leaves. Place one bean
leaf with Persimilis on each tomato plant, weekly, until predators are present on all
plants.
‘Feltiella’: Where humidity above 60% RH can be maintained, the predator Feltiella
acarisuga can also be used with Persimilis. This predator is does best at high mite
densities and in high humidity (for more on Feltiella, see Sheet 280).
Other Measures
• Integrating chemical controls with biological controls is preferred if mites are
detected in a tomato crop. Sprays of fenbutatin oxide (Vendex®), water or
insecticidal soap will help reduce mite numbers and cause minimal harm to
predatory mites.
• 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 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 should be applied (contact biological control
supplier) in August to prevent diapausing mites from over wintering. Pesticides are
less effective against the diapausing form of TSM present in the fall.
WESTERN FLOWER THRIPS
Western flower thrips (WFT) is more likely to be a problem in soil cultures, in
greenhouses recently converted to rockwool culture, or in greenhouse complexes with
ornamental plants on site. WFT cause “ghost rings” on fruit, some feeding damage to
leaves, and can transmit Tomato Spotted Wilt Virus, which is lethal to tomatoes.
Biological control of thrips in tomatoes using predatory mites is difficult because the
toxic, glandular hairs on the plants impede the mites, but other measures described
below can sufficiently suppress thrips on tomato.
Monitoring Tips
• Use yellow 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 the plant
canopy.
SHEET 410- TOMATO
Release Biological Controls
‘Dicyphus’: The predatory bugs will feed on thrips and can survive on tomato if there
are other pests present as well (for more on Dicyphus, see Sheet 280).
‘Cucumeris’: The predatory mites can be used on tomato to control flower thrips (for
more on Cucumeris, see Sheet 220). Because the hairs on the plant impede the
movement of mites, use the bulk Cucumeris product in bran and sprinkle it on to the top
of each infested plant.
Other Measures:
• Avoid thrips infestations by thoroughly cleaning up the crop at the end of the
season: apply naled (Dibrom®) before removing tomato 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.
• Do not keep any ornamental plants in the greenhouse, and maintain a weed-free
border, 3-m (10-ft) wide, around the outside perimeter of the greenhouse.
APHIDS
Aphids (such as the green peach aphid, Myzus persicae) may appear during the spring or
summer. They are relatively easy to control on tomatoes using biological controls so
seldom cause major problems. New infestations are usually detected first on the lower
stem of tomato plants in the course of routine crop management. Aphid populations can
build-up rapidly, however, so do not delay treatment (for more on aphids, see Sheet 340)
The potato aphid, Macrosiphum euphorbiae, can be a more serious problem because its
toxic saliva causes leaf distortions and stunted growth. It is larger than the green peach
aphid, has long slender cornicles pointing back from the abdomen (see Figure 1, Sheet
242), and tends to drop quickly from the plant when disturbed.
‘Aphidoletes’: When aphids are found, release aphid midges Aphidoletes aphidimyza (see
Sheet 240), twice, 1-2 weeks apart.
‘Aphidius’: As soon as green peach aphids are detected, apply the parasite Aphidius
matricariae , (see Sheet 242) weekly until established.
If the potato aphid is detected, use Aphidius ervi as well as Aphidoletes for control.
RUSSET MITES
This microscopic mite (Aculops lycopersici) infests tomato stems and spreads slowly
through the greenhouse. There are currently no adequate biological controls available.
Most growers spot spray affected and nearby plants with dicofol (Kelthane®).
• Mark infested plants and rows; pick and handle these plants separately to avoid
moving the russet mites to adjacent plants and throughout the greenhouse.
Summary of IPM Guidelines Greenhouse Tomatoes
Between crops:
SHEET 410- TOMATO
• 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.
At start of crop:
• Whitefly: Release Encarsia at low rates.
• Fungus gnats: 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.
• Where there is a history of high pest numbers, release Dicyphus.
• Two-spotted mites: Spot treat fenbutatin oxide (Vendex®); apply Persimilis and
Feltiella as needed.
• Russet mites: Spot treat with dicofol (Kelthane®) as needed.
• Aphids: Release Aphidoletes and Aphidius.
