CAUTION: This information was developed for North Carolina and may not apply to other areas.
Biological control is a tool to be considered in constructing an integrated pest management scheme for closed system crop production and maintenance. In a complete IPM program, diseases, weeds, and plant growth must be considered as well as insects and mites, but this note only covers insect and mite pests of greenhouse crops.
IPM is a complex program and each crop must be considered individually. Some greenhouse crops such as tomato and poinsettia are more suitable for biocontrol for several reasons. Tomatoes and poinsettias have relatively few insect and mite pests and they are not grown continually throughout the year, so there is a break in the production cycle. The following management practices will simplify the task of setting up a biocontrol program for a greenhouse crop.
Screening can significantly reduce numbers of insects flying or being drawn into greenhouses. Several screening materials now on the market can exclude thrips. One caution, however, is that the finer the screen, the greater its resistance to air flow into the greenhouse. For specifications on greenhouse screening, see Insect Note No. 104, Insect Screening for Greenhouses.
Clothing - Growers can avoid carrying insects into the greenhouse by not wearing white, blue, yellow or green clothing. Aphids,thrips, and whiteflies are attracted to yellow, green and blue. Thrips are also attracted to white. These insects may jump onto clothing and be carried from one greenhouse to another.
Quarantine - Growers should inquire if their supplier is having whitefly or mealybug problems. At least then growers will know what to expect on the cuttings or plugs. In addition, all plant material should be inspected before it is brought into the greenhouse. New plant material should be kept in a separate section for a week or more before integrating it into the growing area to assure that pests are not introduced into the main growing area. . Thrips, aphids and whiteflies are readily transported throughout the greenhouse industry on cuttings and plants.
Monitoring - Constant vigilance for insects, mites and disease is required for effective pest management. Certain employees should be assigned the responsibility of scouting for insects and other pests on a regular basis (weekly during the winter and twice per week in summer). Written records should be kept of where various pests are found. Pests should be monitored by using yellow sticky cards, yellow pan traps, and by examining the foliage and occasionally the roots. Blue sticky cards work best for thrips.
Record Keeping - A log of pest type, locality, abundance and all pesticides applied should be kept. These records can be of long-term benefit, as many pests tend to appear about the same time each year. Short-term benefits include knowing what pests survive a pesticide application. This alerts the grower to the possibility of poor timing, poor application of the treatment, or pesticide resistance in the pest population. A change in the kind of treatment or pesticide can be made before the crop is significantly damaged.
Pest Identification - It is important to be able to recognize the different kinds of pests in their various stages of development. The North Carolina Cooperative Extension publication, AG-136, Insect and Related Pests of Flowers and Foliage Plants, should be of some help in identifying insects and mites on plants and insects on sticky cards. The most frequently misidentified pests are shore flies and fungus gnats.
Shore flies breed in algae and do little direct damage to poinsettias. However, shore flies are very resistant to pesticides. Fungus gnats breed in decaying roots and over-watered peat moss. Fungus gnats can be very damaging to poinsettia cuttings and plants, but they can be controlled with pesticides. Another misidentification assumes that parasitized aphids are a new kind of tan aphid that cannot be killed with insecticides. Unfortunately pesticides are sometimes expended uselessly against shore flies and parasitized aphids.
Chemical Control - Generally speaking, except for DiPel (B.t.), the use of biological organisms is not compatible with the use of traditional chemical sprays. The brown mummy stage of aphids infected with Aphytis wasps are resistant to soap. Insecticidal soap can be used in conjunction with Encarsia wasps if the soap is applied when the parasites are in the blackscale or brown scale stage.
Biological Control - Some growers use beneficial organisms for biological control where appropriate. Biological control organisms can be used especially effectively for aphid, caterpillar, spider mite and whitefly control.
- Aphids: Aphytis wasps, Aphidoletes aphidomyza maggots, and lady beetles can be ordered through the mail. Aphidoletes aphidomyza can be kept active by burning night-lights. Bug Pro and other synthetic food sources are available to help keep lady beetles from dispersing. Lacewings can also be ordered through the mail. Syrphid maggots may occur naturally where screening is not employed.
- Caterpillars: Bacillus thuringiensis (Thuricide, DiPel, and other) controls caterpillars and can be used with regular chemical pesticides. Green lacewing larvae also prey upon caterpillars.
- Darkwinged Fungus Gnats: Fungus gnats are large enough to see flying and crawling about on the potting mix. Fungus gnats are also attracted to yellow sticky cards if the cards are not hung too high above the pots. Large numbers of fungus gnat adults on the cards indicate to the grower that the roots of the crop should be examined for maggots and their damage. Maggots can be monitored by using slices of potato laid on the surface of the potting mix. Such slices should be sterilized with bleach to avoid contaminating the potting mix with disease organisms perhaps carried on the surface of the potato.
Every few days the slices can be examined for maggots on the lower surface and on the spot the slice had been lying. There are no exact thresholds established for fungus gnats or their maggots, but large numbers of adults flying around and stuck on the yellow sticky traps with six or more maggots per potato slice should indicate the need to start managing this relatively destructive pest. Uninfested media, clean cultural practices and lack of excessive watering help prevent fungus gnat infestations. Since fungus gnats prefer potting mixes containing peat moss and abundant moisture, growers might consider using bark mixes and avoid over watering plants.
Removing organic matter that collects on and under benches should also help. Decoy pots of sprouting grain are attractive to females to lay eggs. Afterwards, the pots should be submerged in hot water or the contents sterilized in some manner every 2 weeks to destroy the eggs and maggots. Darkwinged fungus gnats have few natural enemies. A formulation of Bacillus thuringiensis H14 (Gnatrol) is a biological control organism that infests darkwinged fungus gnat maggots.
A predaceous nematode, Steinernema feltiae, is available in the product ScanMask. The advantage of these nematodes is that they attack darkwinged fungus gnat pupae as well as maggots.
- Mealybugs: The Australian lady beetle, Cryptolaemus montroucieri, is commercially available but it is not available at all times. Lady beetles are somewhat sensitive to pesticides so the grower would have to curtail or eliminate the use of most pesticides (including soaps).
- Spidermites: Predaceous mites are available to control spider mites, but the grower must refrain from using other synthetic insecticides while using the predacious mites. Phytoseiulus persimilis and Amblyseiulus cucumeris mites can be ordered through the mail. These mites have poor shelf life, but they may also suppress thrips. Phytoseiulus degenerans is a mite predator from Morocco that can tolerate very low relative humidity and can be reared on pollen.
- Thrips: Thrips have no very effective biological control organism available. Dick Lindquist at Ohio State found that misting infested plants significantly lowered western flower thrips populations. The more frequent the misting, the greater the reduction of numbers. This reduction of numbers has been reported for other thrips species with overhead irrigation. Although naturally occurring parasites and predators may not seem to have much impact on thrips populations, Leonard Dintenfas observed that western flower thrips populations increased exponentially after the application of pesticides to onions in Texas.
Predaceous insects associated with the western flower thrips include Aeolothrips fasciatus, the insidious plant bug and Orius tristicolor. The parasitic Thripoctenus americensis has been found to utilize the western flower thrips.
- Whiteflies: Encarsia formosa is a tiny parasitic wasp that can be used to control the greenhouse whitefly and silverleaf whitefly. It can even be applied as a "living insecticide" in which case the grower need not expect it to establish a balance of nature in the greenhouse for effective suppression. Most synthetic pesticides are not compatible with Encarsia formosa.
Insecticidal soap can be used in conjunction with Encarsia wasps if the soap is applied when the parasites are in the black scale or brown scale stage. It is possible to integrate these two management techniques. Encarsia formosa can be ordered through the mail, but sometimes occurs naturally.
Eretmocerus wasps are also tiny, encyrtid parasites of whiteflies being explored for biological control of silverleaf whiteflies. Naturalis-L and Mycotrol are formulations of Beauveria bassiana, a parasitic fungus. Our informal demonstrations indicated that Beauveria can be as effective as pyrethroids and organophosphates for whitefly suppression.
Biological control of mealybugs in greenhouses. Whitcomb, W. D. 1740. Massachusetts Agr. Exp. Sta. Bull. 375. 22 pp.
Biological pest management for interior plantscapes. Steiner, M. Y. and D. P. Elliot.1983. Vegreville, AB. Alberta Environ. Centre. 30 pp
Greenhouse IPM with an Emphasis on Biocontrols. PennState Extension.
Greenhouse Manager's Guide to Integrated Pest Management In Northern New England. Parker, B. L. et al. 2008. Entomology Research Lab, Univ. Vermont. 91 pp.
For assistance with a specific problem, contact your local Cooperative Extension Center.
This Insect Note has not been peer reviewed.
Publication date: Nov. 12, 2002
Revised: Oct. 28, 2019
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