Christmas Tree Production in North Carolina

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Biological Control of Pests in Christmas Tree Production

What is biological control? Biological control is man’s use of living organisms to control a particular pest. Biological control can take on many forms. It can be as simple as choosing a pesticide that has the least impact on natural enemies (predators, parasitoids, diseases) or as complicated as going to a pest’s native habitat and importing one of its natural enemies. Controlling pests in Christmas trees is difficult because it is hard to get good coverage with pesticides. By using natural enemies to their full advantage, Christmas tree growers can save money as well as protect the environment.

Pesticides and natural enemies. Most people know that insecticides will kill the good bugs (natural enemies) as well as the bad bugs. But did you know that fungicides and herbicides can also adversely affect some natural enemies? Dr. Douglas Pfeiffer in the Virginia Tech Entomology Department has developed a table of the releative toxicity of pesticides to common orchard predators. These are mainly apple orchard predators but many are also commonly found in Christmas trees. http://www.ento.vt.edu/Fruitfiles/SprayGuide/PredTox.html

Recognizing natural enemies. The following are important naturally occurring predators of some the common pests of Fraser fir Christmas trees and other conifers grown in western North Carolina. Learn to recognize them so that when scouting for pests, you can also take note of any predators found. If a lot of predators are present, it should affect your decision to treat for a pest.

Special note: Remember that the larvae of these predators are most important to find on the tree. Larvae cannot fly off and move to a better site. When they are found on a Christmas tree, they have to feed on the pests there or they won’t survive. Each larva must eat many of their prey before they can grow to maturity – often several hundreds. So when you see one of the adults such as an adult lady beetle, remember that a couple of hundred or more aphids went into producing that beetle!

Syrphid fly larvae are important predators of the balsam twig aphid and may also eat balsam woolly adelgids and spruce spider mites. Look for the green or brown worm-like larval maggots moving through the foliage almost like an inch-worm. The adults are flies. They are often mistaken for sweet bees. The adults do not feed on insects, but must eat pollen and nectar to survive and reproduce. That’s why the flowering weeds in Christmas tree fields are so important – to provide habitat for the adults.

• Photos of adults and larvae are found at http://cipm.ncsu.edu/ent/biocontrol/SyrphidFlies.htm and http://ippc2.orst.edu/potato/syrphidfly.html and http://www.clemson.edu/hort/homehort/bisyrlrv.htm
• Finding the syrphid fly eggs on a Fraser fir shoot is especially important. That means that the adult fly thought there were enough pests for the larva to live on. Photo of syrphid fly egg – http://www.nysipm.cornell.edu/factsheets/treefruit/pests/ben/Ben_fig2.html

Aphid midges are similar to syrphid flies. Their larvae have occasionally been found in Christmas trees eating spider mites and rust mites.

• The aphid midge, Aphidoletes aphidimyza. http://www.nysaes.cornell.edu/ent/biocontrol/predators/aphidoletes.html

Lady beetles and their larvae are voracious feeders of all kinds of pests including aphids, adelgids and mites. There are several species of lady beetles commonly found on Christmas trees in western North Carolina.

One problem with lady beetles is that they will eat each other. Another problem with the adults is that though they are predators, they will fly to another area if there isn’t enough to eat.

• Multicolored Asian lady beetles, also called Harmonia lady beetles, are adapted to living in trees. Their larvae are often found eating twig aphids and they have been observed eating the balsam woolly adelgid. Unfortunately, they are also adapted to hibernating in people’s homes in the winter. There has been some interest in rearing the larvae of these lady beetles and releasing these in tree fields in the spring to control twig aphids. http://www.nysaes.cornell.edu/ent/biocontrol/predators/harmonia.html
• Convergent lady beetles are the ones commonly sold. Some Christmas tree growers have tried releasing these predators, but without much success. Usually, if pests are found, naturally occurring lady beetles and other predators will move in. http://www.nysaes.cornell.edu/ent/biocontrol/predators/hippodamia.html
• Seven spotted lady beetle are sometimes found in Christmas trees, mostly in the cooler months. http://www.nysaes.cornell.edu/ent/biocontrol/predators/c7.html
• Pseudoscymnus tsugae is an introduced predator of the hemlock woolly adelgid. It prefers to feed on hemlock woolly and not balsam woolly adelgid. However, it may occasionally feed on BWA. http://www.nysaes.cornell.edu/ent/biocontrol/predators/pseudoscymnus_tsugae.html

Green and brown lacewing larvae are occasionally found on Christmas trees. I’ve seen them more often in fields where grass is allowed to go to seed around field borders, and in fact the adult lacewings need grass pollen on which to feed.

• Photos of adults and larvae – http://cipm.ncsu.edu/ent/biocontrol/Lacewings.htm and http://www.nysaes.cornell.edu/ent/biocontrol/predators/chrysoperla.html and http://www.hort.uconn.edu/ipm/homegrnd/htms/predators.htm

Dusty wings are in the same family as the lacewings, but are smaller. Not much is known about these small predators. The adults and their larvae are frequently found on Fraser fir foliage in the spring in western North Carolina. They may be an important predator of mites.

• This lacewing site also has information about dusty wings. http://www.hort.uconn.edu/ipm/homegrnd/htms/predators.htm
• Drawings of dusty wing adults and larvae – http://bugs.osu.edu/101/neuroptera/coniopterygidae.htm

Predatory mites are invaluable predators of spider mites in Christmas trees. These mites are about the same size as the spruce spider mite, but they move around a lot more on the foliage. One problem with predatory mites is they prefer humid conditions. That’s one reason why spider mite numbers explode when it gets dry.

The following are some of the important species.

• Neoseiulus (=Amblyseius) fallacis is the most common predatory mite found in Chrismtas trees. It is commercially available and has been released for spruce spider mite control in Christmas trees. http://www.nysaes.cornell.edu/ent/biocontrol/predators/neofall.html
• Phytoseiulus persimilis is one of the commercially available predatory mites. http://www.nysaes.cornell.edu/ent/biocontrol/predators/phytoseiulus_persimilis.html
• Galendromus (=Typhlodromus, =Metaseiulus) occidentalis is another commercially available predatory mite. http://www.nysaes.cornell.edu/ent/biocontrol/predators/galocc.html

Tiphia wasps are parasites of white grubs. These wasps give free pest control, but will be killed out if pesticides are used frequently. For more information on Tiphia wasps, see the Ohio State web site: http://www.oardc.ohio-state.edu/biocontrol/j_beetle.htm

Predatory nematodes. Nematodes in the genera Steinernema and Heterorhabditis feed on white grubs found in the soil. They are available commercially and have been used to control grubs. For more information on using predatory nematodes, see the Ohio State web site on Insect Parasitic Nematodes: http://www2.oardc.ohio-state.edu/nematodes/default.htm

Augmenting natural enemies. Many of the natural enemies found feeding on Christmas tree pests are commercially available. Some Christmas tree growers have tried purchasing and releasing these beneficials to increase pest control. But releasing predators isn’t easy and it is very expensive. It’s hard to distribute tiny predators throughout a Christmas tree field. For more information on the purchasing and application of natural enemies read:

• Biological Control: Purchasing Natural Enemies by David Orr and James Baker http://cipm.ncsu.edu/ent/biocontrol/3a.htm
• Biological Control: Application of Natural Enemies by David Orr and James Bakerhttp://cipm.ncsu.edu/ent/biocontrol/3b.htm

Conserving the natural enemies that are already present in a Christmas tree field means doing everything possible to provide a safe habitat for them. This can be accomplished by:

• Applying a pesticide only when it is found to be necessary through scouting.
• Choosing the pesticide that will have the least impact on non-target organisms such as bees and natural predators. Broad spectrum materials such as chlorinated hydrocarbons (lindane), synthetic pyrethroids (Asana, Astro, Talstar) and often organophosphates will kill the beneficial insects as well as the pests, potentially creating problems with pest resurgence or secondary pest problems in the future.
• Applying pesticides for balsam woolly adelgid control when they will have the least impact on natural predators – typically in the fall or winter.
• Creating a habitat for natural predators by allowing flowering in ground covers and field borders. Many adult predators require nectar or pollen to feed on or to reproduce. By having a diverse ground cover, it is more likely that important predators will find what they like to their taste. Good weeds appear to be yarrow, Queen Anne's lace or wild carrot, mustard, false dandelion, or other simple white or yellow flowers.

Hemlock Woolly Adelgid biocontrol. Although this is a site for Christmas tree pests, many Christmas tree growers are also concerned about the hemlock woolly adelgid. Some of these predators may also feed on the balsam woolly adelgid. The following is a fact sheet from Clemson University outlining the various predators that are being tested and released. http://entweb.clemson.edu/cuentres/eiis/pdfs/bb8.pdf

The following are links to additional information about predators:

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Prepared by Jill R. Sidebottom, PhD, Area Extenson Specialist, College of Natural Resources, NCSU

The use of brand names and any mention of commercial products or services in this publication do not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact an agent of the North Carolina Cooperative Extension Service in your county.

Christmas Tree Home | Research | Production: Mountains / Eastern NC | Marketing & Financial Management
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Updated April 7, 2006