BIOLOGICAL CONTROLS FOR THE GREENHOUSE
(adapted from Oklahoma Extension)
Biological control agents are an important part of integrated pest management systems. Their use must be coordinated with other types of pest management, chemical and mechanical. When considering which agents to utilize, pest species must be carefully identified and the pest populations must be low enough so that bioagents are not overwhelmed. Temperature, humidity and lighting of the greenhouse must be considered; and previous pesticide usage must be taken into account before biocontrol agents are introduced.
Encarsia formosa is a tiny parasitic wasp is used primarily to control
greenhouse whitefly. It should be introduced as a preventative or at low
pest population levels for best results. The wasps lay their eggs in the
third and fourth instars of whitefly larvae. Encarsia are sold as parasitized
whitefly pupae stuck to small cards. The cards are easy to hang on plants
below the canopy, out of direct sunlight. Release rates should average
1 wasp for every 1 to 4 plants per week for 4 to 6 weeks. Higher release
rates may be needed for older, and thus larger, plants.
Encarsia has also been tried for sweet potato whitefly control but with less success. Release rates are higher, 4 to 5 Encarsia per plant for the first 3 weeks, then 1 per plant for 6 weeks. Greenhouse whitefly pupae that have been parasitized turn black, and sweet potato whitefly pupae turn a straw color. When 70 to 80% of the plants contain parasitized pupae, releases may be discontinued.
The wasps do best when daily temperatures exceed 72 degrees F. At lower temperatures, the whiteflies reproduce too fast for the Encarsia to control them, so it is not advisable to release them when day temperatures are below 72 F and the night temperatures are below 59 F, as often is the case in winter. April releases have been successful for some growers. Encarsia lay more eggs in bright light; however, sodium halide lights may kill Encarsia that fly into them. The wasps tend to migrate to drier parts of the greenhouse. Encarsia are readily available from numerous suppliers. To check viability of the wasps, a small portion of each shipment should be set aside in small containers, such as sealed plastic bags or yogurt cups, and emergence observed.
Delphastus pusillusis another biocontrol agent effective against whiteflies. Both the larvae and adults of this small black lady beetle feed on whitefly eggs, larvae and adults. It should be used in conjunction with Encarsia. It has been effective against Bemisia tabaci, the sweet potato whitefly. Availability, however, is limited.
Phytoseiulus persimilis is a predatory mite widely available for the control of spider mites. They are shipped mixed with vermiculite or bran. Check quality by shaking some vermiculite on white paper and looking for tiny orange mites moving around. Better results are generally obtained using locally produced predators, as these often arrive in better condition than imported ones due to shorter shipping time.Care must be taken when releasing the Phytoseiulus. Sprinkle vermiculite on every infested leaf. Order enough for one mite per infested leaf. They become established in the crop in about one week. Beneficial mites prefer moderate temperatures and humid conditions (60-90% relative humidity). Spider mites have been successfully controlled by releasing 10 predators per plant. Phytoseiulus has also been used on Gypsophila (Baby's Breath) and has been effective from two to seven months. Exercise care when using miticides near Phytoseiulus. Abamectin (Avid) will indirectly kill beneficial mites that feed on treated spider mites.
Other beneficial mites that are available include: Phytoseiulus longipes, Amblyseius californicus and Galendromus occidentalis. Each of these species is suited to a different environmental condition that should be considered when ordering. For example, Phytoseiulus persimilus does best in fairly humid conditions under 85 degrees F. There is a strain of P. persimilus adapted to high temperatures that tolerate temperatures over 100 degrees F with lower humidity. P. longipes can handle temperatures over 100 degrees F and has the lowest relative humidity requirement of commercially available predatory mites—40% at 70 degrees F (higher relative humidity required at higher temperatures). Amblyseius californicus tolerates slightly warmer temperatures than Phytoseiulus persimilus with lower relative humidity requirements. Most dealers are willing to assist growers in selecting the proper biological control agent for their greenhouse environment.
Steinernema (=Neoaplectana) carpocapsae are beneficial nematodes that attack numerous insects in the soil. A moist environment and appropriate application rates are the two main requirements for success. The nematodes can be supplied in a spray concentrate or a moist granular carrier. A smaller hybrid strain of Steinernema is especially suited to the warmer environment of the greenhouse. Apply 70,000 per sq. ft. of soil surface, preferably in the evening. Some growers apply them using injector systems or diluting them with water and using a pump sprayer, hose-end sprayer, watering can or pail. They will survive in oxygen-rich water, such as produced by nutrient film technique systems, but may "drown" if left in standing water for more than a few hours.
Amblyseius cucumeris and A. barkeri (=mckenziei) are thrips predators which are widely available. They are tan-orange mites that are similar in appearance to spider mites. They prey on Western flower, onion, broad and cyclamen thrips. They are best used as a preventative measure in ornamentals, before any evidence of thrips occurs. They prey only on the larval stages of the thrips, and they cannot control an established thrips population. These predators are relatively inexpensive. They are received in containers of loose bran which is easily sprinkled on the foliage of the plant. A suggested release rate is 10 to 100 per square meter, weekly. Other sources suggest an introduction rate of one predator per square foot, followed on a monthly schedule. Amblyseius spp. preform best in warm, dry weather. They enter diapause and are not effective between September and March unless night temperatures remain above 70 degrees F.
Hippodamia convergens, ladybugs, feed on aphids and spider mites, both in the larval stage and as adults, but ladybugs do not always provide successful, long-term control. However, they are useful to "knock down" an infestation. Availability is good, except during the early summer months when supplies may be sold out. Ladybugs may be kept in the refrigerator for several weeks and released one handful at a time. They are usually thirsty when released, so plants should be misted prior to release. Since ladybugs have a strong dispersal instinct, spraying them with diluted soda pop will cause their wings to stick together and keep them from flying. Releasing them in the evening is also helpful.
Aphidoletes aphidimyza is a predatory midge commonly known as the aphid
predator. The tiny orange larvae of this predator attack and kill aphids.
The adults resemble tiny mosquitoes. They are effective against many species
of aphids, but not against the melon aphid. The midges are shipped in the
pupal stage, mixed in either small bags of vermiculite or peat moss. Cut
a one inch hole in the top of the bag and place it at the base of an aphid-infested
plant. Keep the vermiculite or peat damp but not saturated. Adults will
emerge in seven to ten days. Adults fly at night and lay eggs in aphid
colonies. Since only the larval stage attacks aphids, overlapping generations
must be maintained. Repeat the application in two weeks. Suggested release
rate is one cocoon per 10 square feet of greenhouse or a target level of
1 larvae per 15 to 20 aphids.
Short days will cause A. aphidimyza to enter diapause. Lighting with 80 to 100-watt bulbs at night will prevent diapause. The optimum temperature for the midge is 73 degrees F. This predator works especially well on long season crops such as lilies, roses and chrysanthemums and in greenhouses with in-ground beds or gravel floors because it pupates in the soil.
Cryptolaemus montrouzieri is a beneficial lady beetle known as the mealybug destroyer or mealybug predator. It prefers warm temperatures (72-77 degrees F) and is not effective during the winter months. The adult and larva are predaceous and attack mealybugs and scales. Release rates vary with pest population, approximately 2 per square meters or 2 to 5 per infested plant. Release at various infestation sites. Repeat releases may be necessary. Citrus mealybugs may also be controlled by Leptomastix dactylopii. This parasitic wasp prefers sunny environments with warm temperatures of 74 to 80 degrees F. Control takes one to three months.
Sources of biocontrol include: IPM Laboratories, Main St, Locke NY 13092-0099 (315) 497-3129. The Green Spot, Ltd. 93 Priest Rd., Nottingham NH 03290 (603) 942-8925. Koppert Biological Systems, Inc. 28465 Beverly Rd., Romulus MI 48174 (734)641-3129. No endorsement of these or discrimination against other suppliers is intended.
TEST COMPOST-BASED POTTING MIXES EARLY
It seems like every year, some growers report problems in plant growth when using compost-based potting mixes for organic transplant production. If you are making and/or using an organic potting soil, getting it tested every year makes sense to avoid problems such as lack of available nitrogen, or excess salts. It is also helpful to test annually in order to have documentation of mix characteristics when there are no problems. The UVM Agricultural Testing Lab, Hills Building, Burlington VT 05405-0082 offers the following tests: Compost Analysis ($30) includes nutrient content (total N, P, K, Ca, Mg, Fe, Zn, Cu and B), C:N ratio, and soluble salt level. Add $2 for pH analysis. Use this test to assess compost BEFORE it is used in making a potting soil. The Potting Soil Analysis ($15), also called the ‘Saturated Media Extract' test, measures available nutrient levels (nitrate, P, K, Ca and Mg), soluble salts, and pH. Use this test after making or buying potting mixes - but BEFORE planting lots of flats! Send a quart of material to the lab to assure they have enough to work with. Turn around time ranges from 1 to 3 weeks. In addition to the lab tests, it is advisable to make test plantings of crops (bioassay) as early as possible. For more information contact the Ag Testing Lab at 802-656-3030.
IMPLEMENTING A GREENHOUSE IPM PROGRAM
(Adapted from UVM Tri-State Greenhouse IPM workshop, 2000)
Start with a clear concise plan (1 greenhouse, 1 problem). Define objecties and goals: which crops, which insects and diseases. List current control practices. Gather background info on the crop and the problems. Determine scouting techniques and who will scout (1 or 2 people), how, when, what training is needed. Perform an initial site inspection (before plants even arrive). As soon as crop is growing begin regularly scheduled scouting using zig zag pattern, looking at plants randomly, ideally 10% of the crop if possible. Examine up-close, use scouting tools such as hand lens. Correctly record results (keep a notebook)... immediately. Analyze results and observations...what are you seeing; brainstorm solutions. Make decisions, order biocontrols, apply chemicals as necessary, know the effects of residues on biocontrols. Practice good sanitation by removing weeds, plant residues, and old crop plants. Check cement cracks, stone floors carefully for weeds. Keep hoses off the floor - hang them downward to help hose end dry out, reducing spread of disease. Examine purchased plants when they arrive, before putting them into the greenhouse. Always remove infected or heavily infested plants: preferably get rid of or treat away from clean plants. Use screens over ventilation openings to keep pests out. Avoid tall vegetation around greenhouse, especially outside vents - at least 10 foot mowed swath around greenhouse is recommended.