Successful Biological Control of and Mites in Greenhouse Tomatoes

Carol Glenister, Entomologist, IPM Laboratories, Inc. PO Box 300, Locke, NY 13092, Phone 315 497-2063

Why are whitefly such a problem in greenhouses? Are they a problem in field tomatoes? What about ? Or spider mites? Have you ever seen a spider mite outbreak on tomato plants in the field? The first part of this presentation discusses the reasons that beneficial insects can not accomplish their normal tasks in the greenhouse without your help. The second part of the presentation is an overview of the beneficials that are currently used in tomato greenhouses for control of insects and mites. This is followed by a discussion of summer 2005 demonstrations of creating “habitat” to support beneficials in greenhouses

♦Physical Barriers: The most obvious physical barrier is the greenhouse wall. The wall prevents natural enemies from getting into the greenhouse when pests start to flare. Thus in the summer, one easy way to control whiteflies on an individual plant is to simply put the plant outside. The whiteflies usually disappear. For example, Lantana produces abundant whitefly in the greenhouse, but not in the garden. control is a similar story. Aphid parasites and predators such as Syrphid , lady beetles, aphid , and lacewing larvae will zero in on outbreaks fairly quickly in the outdoor garden. But they often can not get into the greenhouse in time to be able to minimize the aphid damage there.

♦Climatic disruption: Pest flare-ups also occur when climatic conditions make it difficult for predators and parasites to even inhabit certain plants. For example, many predatory mites for spider mite control do not tolerate hot, dry conditions. That is why we associate hot, dry conditions with mite outbreaks. One solution is to make sure that spider mite populations stay low during the cooler, humid months so that there are few reproductive adults available to start an outbreak when it becomes hot and dry. Another might be to create some habitat at the base of the plant where the beneficials can shelter from the inhospitable climate.

♦Pesticide disruption Many pesticides kill beneficials better than they kill the pests. The result is that after initial knockdown, pest levels can rise higher than they were before the treatment. The solution is to choose pesticides that are compatible with beneficials. Soaps and oils do not harm insects as soon as they are dry. growth regulators such as Enstar, Talus, and Distance are not poisons, but instead interfere with pests life cycles. Their influence on most natural enemies, if any, lasts for about a week.

♦Inappropriate habitat Many predators and parasites need support from the environment in the form of pollen, nectar, resting places, or prey availability. One example is the thrips predator, Orius insidiosus. Orius prefers to be where there is a pollen food source. If there is no pollen available, it is very likely that they will leave the greenhouse shortly after you release them. It is even pickier than that: Orius thrives on pepper plant pollen but does not on tomato pollen. Parasites often do not absolutely require flowers, but they will live much longer when there is nectar available. Some varieties of grapes are more hospitable to predatory mites, literally offering little tufts of hair on leaf undersides for the mites to shelter under. Yet in other cases, such as on tomatoes, sticky hairs irritate and impede the movement of predatory mites.

Some natural enemy populations simply require food in the form of prey or hosts. These species will disappear when prey or hosts are scarce.

Natural Enemies for Whitefly Control Encarsia formosa was first used for control of whitefly in greenhouses in the late 1920’s and is still the most effective biological control of greenhouse whitefly today. Beware, however, wherever ornamentals are also grown, there is a good chance of becoming infested with silverleaf whitefly, also known as Bemisia. Encarsia is not very useful against silverleaf whitefly, for which you need to obtain an Eretmocerus sp. In all cases, excellent control can be achieved if the parasites are released weekly after the first sign of the pest. After 4 to 6 weekly releases, the parasites often will maintain control season long unless more whitefly are brought into the greenhouse on another crop. Anyone who waits until several generations of whitefly turn over before starting parasite releases will have great difficulty in regaining control, because a few generations will produce a hundred to a thousand fold more whitefly for the parasites to attack.

Delphastus catalinae is a tiny lady beetle which specializes in whitefly eggs and small scales, but it does not seem to establish in tomatoes well, and is therefore not used much.

Natural Enemies for Aphid Control This is yet another pest where identification is very important to control by parasites. There are three parasitic wasps used in tomato greenhouses. Aphidius colemani attacks melon aphid and green peach aphid, but not potato aphid which also is a common pest in greenhouse tomatoes. The more pricey Aphelinus abdominalis and Aphidius ervi attack potato aphid. It is important to repeat parasite releases at least once a week or two after the first release in order to create overlapping generations.

Aphidius colemani can be maintained on banker plants of barley infested with cereal aphids. This is being done in a hydroponic lettuce facility, Fingerlakes Fresh, near Ithaca NY. European glasshouses have used a grass aphid to support aphid parasites in greenhouses for more than 30 years. Since the aphid does not attack broadleaf plants, it does not pose a threat to broadleaf crops. The aphids are grown on barley or rye. Finger Lakes Fresh, a hydroponic lettuce producer near Ithaca, NY uses a small station of barley banker plants (approximately 10 square feet of banker plants) to service the 8000 square foot facility. Barley is grown first without aphids and then placed in a cage which contains aphids but screens out the parasites. When the barley is well infested with aphids, it is placed directly in the greenhouse, where the parasites find it and begin to reproduce on this fresh host supply. These same parasites patrol the undetectably low aphid population in the lettuce crop. This system works for producing Aphidius colemani and A. matricariae, but does not work for the very large potato aphid parasites, Aphidius ervi because the cereal aphids are too small to be hosts for these large aphids. In the case of potato aphid, the banker plants can be used to support that aphid predatory , Aphidoletes aphidimyza.

One way to get around the aphid identification question is to release the predator Aphidoletes aphidimyza which kills many species of aphids. This is a gnat-like which lays eggs in aphid colonies that hatch into tiny orange larvae that are voracious aphid predators. Aphidoletes must be released every week for 2 or more weeks in order to create overlapping generations. When daylength is short, they will stop reproducing unless given supplemental light to lengthen the days. The light can be low intensity. Even a street light outside the greenhouse may suffice. A second strategy is to release very small numbers every week and not support reproduction with supplemental lighting. In this strategy, it is important to NOT release the Aphidoletes near known.aphid hot spots which will slow down their searching for the aphid hot spots that you have not detected. They are excellent searchers and

Natural Enemies for Thrips Control Neoseiulus cucumeris, commonly called Cucumeris, is a predatory mite used for thrips control in tomatoes. It is available in bran that can be shaken from a bottle, or hung from the plants in little packets. With Cucumeris, we strive to create continuous presence of the mites for 4 or more weeks. Since they do not reproduce well on tomato plants, they must be reapplied every 2 weeks for the loose material, or every 3 to 4 weeks for the hanging envelope. It is essential for continuous presence of Cucumeris, because the mite only kills the first instart (a larval stage) of thrips after the egg. The predator does not attack adult thrips or second instar thrips.

Orius insidiosus is a predatory bug which does not do well in tomatoes, although it is excellent for controlling thrips on peppers. It may be possible to establish Orius in tomato greenhouses on habitat plants as has been done in herbs and experimental potatoes in greenhouses. This system was developed and used by Brian Bell of Boyce ThompsonT Institute, for Plant Research in Ithaca, NY. He grew marigold plants to provide pollen and habitat for the Orius. This worked particularly well in maintaining Orius because this predator does not need prey in order to reproduce. It can reproduce on pollen alone. The program was so successful that he only had to make one release of 500 Orius onto 60 marigold plants per season in April to gain in season-long control. Brian repeated this procedure successfully for 5 years, then the experimental potatos were no longer needed

Natural Enemies for Spider Mite Control The predatory mites that are used for spider mite control in other greenhouse crops do not find tomatoes to be very supportive habitat. The sticky hairs seem to be a particular problem for these predators and seem to prevent them from traveling freely around plants. However, the tiny midge called Feltiella acarisuga thrives in tomatoes with spider mites. It does very well in spider mite hot spots, and can fly among hot spots, a better mode of transportation than the mites crawling mode. It is best to release Feltiella when spider mites are first seen so that it can establish a breeding population early.

Natural Enemies for Fungus Gnat Control Fungus gnats can be controlled with beneficial nematodes (Steinernema feltiae) or predatory mites (Hypoaspis miles). For best results, they should be applied when the crop is first started.

Habitat Pot Demonstrations in Herbs and Ornamentals In 2005, IPM Laboratories received a NorthEast Sustainable Agriculture Research and Extension grant to demonstrate the use of habitat for supporting natural enemies in a retail herb greenhouse at Baker’s Acres of North Lansing. We established the herb stock house as a control that had no habitat plants. With the advice of the growers, Reenie Sandsted and Cathy Kessler, we chose 4 plants to include in “Habitat Pots” that hung about a foot over each herb bench. We chose Alyssum for early season nectar and pollen, marigolds for season long pollen and Orius harborage, lantana for hot-season blooms, and barley-cereal aphid banker plants to support aphid natural enemies. A similar strategy was tested at University of Vermont in bedding plant greenhouses and at Cornell University in thrips-infested bean plants.

We released Orius on April 11 and May 2, 500 into the control house and 500 into the retail herb house each time. The first release did not seem to establish itself. We believe that the marigold blooms were not open enough to provide abundant pollen at the time of the first release. The Orius established after the second release and its numbers increased season-long. However, thrips damage was rampant throughout the nursery this summer, and even occurred on the marigold plants that were harboring the Orius. Next year we will attempt to have much lower populations of thrips throughout the nursery season- long.

We released 250 Aphidius colemani per site on April 11, and April 18.. In the house with habitat pots, the parasites were released directly onto the barley with its cereal aphids, an instant food source. There were few to no aphids in the “control” stock house at the time of release. We simply freed the aphid parasites in the “control” stock greenhouse. Many cereal aphids and aphid mummies developed on the banker barley. These aphid parasites moved onto the few green peach aphid that dared to appear on the herb plants in the “habitat” herb house. No aphid problems occurred in the “habitat” house all summer. Other predators appeared naturally on these habitat plants including Syrphid flies, lacewing larvae, lady beetles, and in July, Aphidoletes (the aphid midge) became abundant on the banker plants. Instead of waiting 3 months, we could have introduced Aphidoletes in April, but we were afraid they would outcompete the aphid parasites. The Syrphids found the aphid banker plants almost as soon as the doors to the greenhouse were left open for ventilation.

Overall, we were very happy with the outcome of this first attempt to intentionally create and document habitat for natural enemies. Habitat and Banker plants allow us to introduce natural enemies before the pest appears. Our next step will be to carefully document pest control in addition to natural enemy establishment.

Acknowledgements Brian Bell, Boyce Thompson Institute for Plant Research Bob Ladue, Cornell Controlled Environment Agriculture Greenhouse USDA Northeast Sustainable Agriculture Research and Education Grant ONE05-037 and Baker’s Acres of North La