The following are recommended management practices that simplify the task of setting up a biocontrol program for a greenhouse crop and then there are some sources of natural enemies.
Screening
Screening can significantly reduce numbers of insects flying into greenhouses. Even thrips can be excluded by several screening materials now on the market. A word of caution: the finer the screen, the greater its resistance to air flow into the greenhouse. For specifications on greenhouse screening, see Baker et al. (1993).
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.
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 incorporating the new material into the production area (highly resistant thrips, aphids and whiteflies are readily transported throughout the greenhouse industry on cuttings and plants) to assure that pests are not integrated into the main production area.
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 the winter and twice weekly 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.
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 alert 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 Recognition
It is important to be able to recognize the different kinds of pests in their various stages of development. The North Carolina Cooperative Extension Service 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 which cannot be killed with insecticides. Unfortunately pesticides are sometimes expended uselessly against shore flies and parasitized aphids.
Chemical Control
Generally speaking, the natural enemies used in biological control are susceptible to many chemical sprays. However, some chemical products are compatible with natural enemies, and are listed in Table 1. Certain stages in the life cycle of natural enemies are more resistant to pesticides. For example, the "brown mummy" stage of aphids infected with Aphidius wasps is more resistant than other stages, as is the "black scale" or "brown scale " stage of Encarsia wasps.
Sources of Natural Enemies
The Green Spot,
93 Priest Rd., Nottingham, NH 03290-6204, Tel: 603-942-8925, Fax: 603-942-8932
Ciba Bunting North America,
PO Box 2430, Oxnard, CA 93034-2430, Tel: 805-986-8265, Fax: 805-986-8267
Koppert USA,
2856 South Main St., Ann Arbor, MI 48103, Tel: 313-998-5589, Fax: 313-998-5557
Members of the Association of Natural Bio-control Producers
References
Baker, J. R., M. B. Crouse and E. A. Shearin. 1993. Screening as part of insect and disease management in the greenhouse. North Carolina Flower Growers Bull. 38(4): 12-17.