Biological Pest Control Success in Greenhouse Tomatoes

Greenhouse tomato is an ideal crop to apply biological pest control, as there are relatively few pests and well-established programs available. Problems with pesticide resistance and lack of registered pesticides led British Columbia growers to develop and use biological pest control alternatives. The use of bumblebees for pollination also favored the shift from chemical to biological pest control of insects and mites on this crop. The following guidelines are based on successful programs that have been developed in Canada over an 18-year period and have led to the majority of vegetable greenhouse growers using biological pest control.


  1. Start clean.
  2. Monitor for pests early.
  3. Start treatment without delay.
  4. Use recommended rates and release frequencies
  5. Use suppliers as resources at first sign of problems.


1. Starting with low pest levels is critical to success using biological control. Choose products selected for clean up between crops with care. Fungicides will not kill insects or mites. If pests are a problem in the crop at the end of the season, treat the standing crop before pulling and again after removal with the appropriate pesticide. Keep the heat on until after treatment to avoid sending large numbers of mites and thrips into hibernation. Use pesticides with shorter residual effects if biocontrols are to be used in the next. Apply fungicides and cleaners last as they will often help remove and break down pesticide residues.

2. It is cost effective to visually monitor the crop on a weekly basis and use sticky cards. Use 3″X 5″ yellow sticky card traps at a rate of 1 for every 100 plants or about 25 cards per acre. Hang cards just above the plants to catch most dying insects (e.g. fungus gnats, whitefly, thrips, aphids, lygus bugs, and moths). Replace or add new cards every 5 weeks as the glue dries and will no longer trap small insects such as whitefly. Use a felt pen mark to cover the insect once counted to prevent repeat counts. To help identify many pests use a 5-power headband magnifier or hand lens. Walk the rows at least once a week checking cards, scanning the crop and leaves for damage and recording results. If you do not have the time, assign and train a staff member or use a professional monitoring service. Some growers have excellent success by giving all the responsibility (maintenance, harvesting and IPM) for specific greenhouse sections to individuals who then compete for best results and maintain records for their sections. Once all personnel are involved in an IPM program it can become a very powerful and positive force. Be able to identify the various stages of the major pests and their damage. If in doubt, contact or send samples to your Agricultural extension service or biological supplier. Pictorial resources are now more available and in the future there will be direct video internet diagnosis and it will simply be a matter of selecting the appropriate samples. Record trap counts on a weekly map or report for thrips, whitefly, fungus gnats, lygus, and other flying insects (e.g. 5 trapped thrips could appear as T-5, 10 whitefly as W-10). Some pests such as mites and aphids are clumped in distribution and would take far too long to count so damage ratings similar to the following have been used to estimate levels.

M-1 mites detected
M-2 1/5 of leaf damaged
M-3 1/3 of leaf damaged
M-4 entire leaf damaged
M-5 webbing and stringing
A-1 aphids detected
A-2 aphids on aphids on old and new growth
A-3 aphids covering some leaves
A-4 aphids covering old and new leaves
A-5 leaves, plant and floor sticky

A greenhouse map is an extremely valuable monitoring tool to follow records of pests and beneficials as they progress weekly. As a visual aid, it is a good idea to mark the initial infestation sites as well as pest hot spots by hanging different colored survey flagging tapes above the plants and at row ends. Row numbers should be clearly marked on support posts for easy reference. Some intensive IPM greenhouses are now numbering all support posts to use as map grid reference points. This enables quite precise location of pests and by using hand held electronic data-recording devices, information can be downloaded to a computer where it can be analyzed or used in an IPM management program.

3. Act without delay when a pest is identified. Pests can build very rapidly under greenhouse conditions so IPM strategies based on past seasons pest levels often involve “preventative” introductions of biological control agents even before the pest has been detected. Many biological control agents (e.g. whitefly and aphid parasites, Hypoaspis predatory mites) are very good at finding their host at low densities and will take too long to provide control if their introduction is delayed until host populations are higher. Other pests such as spider mite descend onto the crop over a period of time and must be treated with “curative releases” of biological control agents as soon as the pests are detected. Releases must be continued until the biocontrol agents are well established on all infested plants.

4. Use recommended rates, methods, and release frequencies. If using a biocontrol make sure temperature and hours of daylight are not limiting. Whitefly parasite activity is greatly reduced at temperatures below 180C and introduction numbers must be increased. Predators such as Aphidoletes will stop laying eggs and enter diapause when daylight hours become less than 16 in March and September. When using pesticides, spot treatments, reduced rates and short residue periods are important to minimize harm to the biological control agents. One major advantage to a monitoring program is that the rates and release frequencies can be related to the pest and predator levels for optimum efficiency and this should pay for itself in saved costs and improved pest control. It is critical to use recommended rates and introduction schedules. Know what to look for so biocontrol agents are not removed from the crop when pruning leaves. Poorly timed or excessive deleafing can upset an entire program for the season as most of the biocontrol reproduction occurs on the crop.

5. Use suppliers as resources to solve problems.

Biological control technology is a rapidly changing area and there are many variables to consider in every pest control program. Live predators and parasites are very perishable and must be checked for viability on delivery and handled carefully under the appropriate conditions. Release instructions should include life history and handling information. Once released into the greenhouse the biological control should establish and be found cycling on the pest. This may take 2-6 weeks and may be difficult to detect at low pest densities. Contact your supplier or the biocontrol producer at the first sign of any problem for help and to determine the best solution.

Successful biological control of insects and mites is basically a numbers game with a few very serious pests. A simulation model for populations of spider mite and the predator, Phytoseiulus persimilis predicts that controlling a 5 times higher mite population will require introducing 20 times the number of predators. This points out the importance of timing to prevent excessive plant damage and make biological control programs work. The following table is only a brief outline of a biocontrol program for greenhouse tomato. Detailed guides are available from suppliers for other pests on different crops and these should be consulted in planning your own program.

spider mite




Clean-up at end and between crop
 thiodan, soap  thiodan, soap Thiodan,  soap thiodan,  soap
Early monitoring
damage on older leaves adults on yellow traps adults on yellow traps damage on older leaves
Start weekly treatment


Use recommended rates and release frequencies

1+ Phytoseiulus persimilis per infested leaf


Feltiella acarisuga 250/hot spot

Encarsia formosa
1/plant preventive
2-6/plant curative
Delphastus catalinae
0.5/ plant

Hypoaspis miles
1 litre/1000 seedlings (.25 gal/1000 seedlings)

20 litres/ha (2.1 gal/A)
Amblyseius cucumeris
100/infested plant

Aphidius ssp.
0.15/m2 preventive (.13/yd2)

0.5/m2 curative (.4/yd2)
Aphidoletes aphidimyza
1/plant in infested area

Use your suppliers as resources at first sign of problems
You may be in trouble if mites are damaging entire leaves and webbing or stringing You may be in trouble if whitefly adult numbers exceed 20/plant You may be in trouble if thrips numbers exceed 2 adults/flower or 5 larvae/leaf You may be in trouble if aphid damage covers stem or appears on new leaves
Signs of success predators on all infested plants few hot spots. 85% parasitism reduced leaf damage aphids eliminated

For a list of biological control producers and suppliers, visit the website for the Association of Natural Biocontrol Producers.

By: Don Elliott, Managing Director, Applied Bio-Nomics Ltd, 1174-West Saanich Rd, Sidney, British Columbia, Canada V8L5P5

Reprinted from: Proceedings. 1997 New England Vegetable and Berry Growers Conference and Trade Show. Dec. 16-18, 1997. P.154-157.

Updated by: T. Jude Boucher, IPM, University of Connecticut. 2012

Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

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