Greenhouse pest control using beneficial insects has become commonplace and much simpler in recent years. Availability of many beneficials has expanded significantly, and price has come down. In addition, research has established best control methods for many common insect pests. If you have never tried biological control in your greenhouse, this spring might be a good time to start.

Scouting is the first key to success with beneficial insects. You must regularly and methodically inspect your plants for the first signs of insect pests. Then you must be ready to spring into action when pests appear. Beneficial insects take a few days to get to your greenhouse, and several more days to start work, so it’s imperative that you act quickly before the pest population explodes.
This article will tell you the most common greenhouse pests so that you can learn in advance to identify them. If you use the Internet, you will find links on the Follow Up page of the GFM web site (www.growingformarket.com) to sites that help with pest identification. If you don’t have Internet access, the Green Methods Manual is a $9.95 book (shipping included) with insect identification and control information from beneficial insect supplier The Green Spot, Ltd. Contact information is at the end of this article.

This article also will tell you the usual biological controls for common pests, and provide contact information for companies that sell those controls. Hang on to this article, and you’ll be ready if you need to deploy beneficial insects.

Much of the information from this article comes from Lea Westervelt, greenhouse manager, and Chuck Marr, professor of horticulture, at Kansas State University. They have been working for the past four years to convert the university’s 44 teaching and research greenhouses from chemical pest control to biological controls.

“It’s a tremendous effort requiring a tremendous amount of scouting daily observation. You have to be on top of things to be able to respond,” Marr said. Unfortunately, you can’t take preventive action because most beneficial insects need to have a certain number of their prey present in order to survive. “I would probably not introduce any beneficial insects until you see the very initial stages of pest development, or you have historical experience that tells you you’re going to have a certain pest problem,” Marr said.

Besides scouting with your eyes and a magnifying lens, yellow and blue sticky traps can help you spot insect pests when they first appear. Here are the most common greenhouse pests to watch for:

Aphids
Many species of aphids are pests. Most species are similar in feeding habits and reproduction. Aphids weaken the plant by draining its fluids, causing severe distortion of growth, and they often transmit plant viruses.

Aphid midge, Aphidoletes aphidimyza, attacks and kills aphids when it is in the larval stage. Adults resemble tiny mosquitoes. The short days of winter cause it to enter diapause, so the greenhouse should be lighted at night with 60-100W bulbs. It pupates in soil or media, and works well in soil beds.

Aphidius colemani is a small wasp (1/8”) slightly longer than the aphid, and aphids that are parasitized turn into mummies and change to a tan color. Remove yellow sticky traps when these are released, as they are attracted to yellow just like pests.

Lady beetles (Hippodamia convergens) are good for short-term knock-down and very inexpensive. Mist plants before releasing them, as they are usually thirsty after being released.

Lacewing (Chrysoperia) are generalist predators that will attack any soft-bodied insect, especially when hatching. At 80° F, the green Lacewing eggs will hatch in about 4 days. The larvae are best known for attacking aphids and each is capable of killing 30 to 50 aphids per day. Many aphids are eaten but many more are killed by being punctured by the Lacewing larvae. Each larvae will feed for about 3 weeks, then will roll up into a little white pupae and emerge as an adult in about 1 week ready to mate and lay about 100 more eggs. The adult Lacewing does not feed on aphids. The complete Lacewing life cycle takes 4 – 6 weeks.

To prevent a high percentage of the Lacewing population from being in the pupal, adult or egg stage at the same time, you should make two or three releases, two weeks apart. Lacewing larvae are good general predators and will also feed on whitefly larvae and other plant pests.

Whitefly
The two most common species found in greenhouses are the Greenhouse Whitefly and the Silverleaf Whitefly. Feeding by the pests causes a large amount of “honeydew” on the plants. A black sooty mold can grow then, which interferes with photosynthesis.

A reliable beneficial insect for Greenhouse Whitefly is the parasitic wasp Encarsia formosa. After releasing Encarsia, you should maintain greenhouse temperature at 72°F days, 59°F nights, or higher. At lower temperatures, whitefly reproduce too fast for Encarsia.

The Silverleaf Whitefly is not controlled by Encarsia, so a more expensive wasp, Eretmocerus eremicus, must be used.

It’s important to know which kind of whitefly you have – the Follow Up section of www.growingformarket.com has a link to a USDA site the helps you differentiate among whitefly species.

Spider mites
The two-spotted spider mite or red spider mite is a major pest in vegetables, tropicals, and other ornamentals. It is very small and hard to spot, especially because it feeds on the bottom side of leaves. Spider mites feed on plant cells and produce small, yellowish, speckled feeding marks. Webs can be found on heavily infested plants, which will soon wither and turn brown.
Four species of predatory mites, used for different environmental conditions, are very effective when applied as recommended. These predatory mites will multiply nearly twice as fast as the spider mite population. Predatory mites feed only on other mites, not on plants. Short shipping time is important; pay for overnight shipping, and release immediately. They should become established in about a week. Check with the supplier for recommendations about which type of predatory mite matches your conditions.

Thrips
Two types of thrips can be pests in the greenhouse – Tobacco or Onion thrips (Thrips tabaci) and Western Flower Thrips (Frankliniella occidentalis). Both are very small (about 1/50th of an inch), but signs of their feeding are noticeable. Thrips nymphs and adults scrape plant tissue to induce the flow of plant juices, causing the tissue to dessicate and turn white. Thrips are capable of pupating and multiplying most rapidly during periods of warm, dry weather. When growing media and greenhouse floors are kept on the dry side, thrips will multiply rapidly.

While no single method is 100% effective against thrips, using several beneficial insects can keep thrips populations in check. Amblyseius cucumeris, one of the predatory mites used for spider mite control, are best applied early as a preventative, especially on cucumber. They prey on larvae of thrips but cannot control an established population.

Other thrips predators include Hypoaspis miles and the beneficial parasites Steinernema Sp, also known by the trade name Guardian. The minute pirate bug, Orius, eats thrips and many other insects, including other beneficials.

Sources

•Association of Natural Bio-Control Producers, 714-544-8295; www.anbp.org; this group provides a list of beneficial insect suppliers.
•Hydrogardens Inc. has an excellent web site with extensive information to help you identify pests and select appropriate beneficials. www.hydro-gardens.com; 888-693-0578.
•The Green Spot, Ltd., 93 Priest Road, Nottingham, NH 03290; 603-942-8925. Send $9.95 for the Green Methods Manual, or call with a credit card to order.
•North Carolina State University has an excellent web site on greenhouse biological controls, including a chart of pesticides (many of them organic) that can be used along with biologicals. http://ipmwww.ncsu.edu:8150/biocontrol/2a.htm
•Other web sites can be found on the Follow Up page of www.growingformarket.com. Also, the Plant Facts Database, found on the Links page of the GFM site, can be used to search for information on other greenhouse pests.