Integrated Pest Management in the Nursery
Christine Casey
Department of Entomology, NCSU

Management of insect and mite pests in the nursery has been quite a challenge for North Carolina growers in recent years. New problems such as the Asian ambrosia beetle have appeared, while traditional pest control products have left the market or become more restricted in their use or availability.

WHAT’S NEW IN NURSERY IPM?
Recent changes will have a significant impact on how we manage pests in the nursery. Resistance management labeling now mandates pesticide rotation. So it is no longer legal to use repeated applications of a single product to control a persistent pest such as spider mites. Growers need to plan ahead so that they have an adequate supply of the appropriate pesticides on hand.
Legislative changes are leading to the replacement of many traditional pesticides with new materials that often work quite differently. The whitefly product Endeavor is a good example. This is a pesticide that does not kill insects. Instead it acts against whiteflies and aphids by paralyzing their mouthparts so they cannot feed and thus starve to death. While feeding stops in about an hour, mortality may take several days. In some cases these new products will not have the same efficacy or will be more expensive. In the past, for example, chlorinated hydrocarbons (e.g. lindane) or organophosphates (e.g. dursban) could be used to provide reliable, long-term borer control. As these products have been removed from the market they have been replaced by the more expensive pyrethroids.
The continued popularity of perennials means that a more varied range of plant material is being overwintered in the nursery, raising the possibility of new pest introductions. Some herbaceous perennials are susceptible to the thrips-transmitted tospoviruses impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV).

HOW DO I COPE WITH THESE CHANGES?
Growers will no longer be able to rely only on broad-spectrum, long-residual materials for pest management. New pesticides tend to target fewer pests and may not kill all lifestages. This means that scouting and proper pest identification will be essential for effective management. Research to develop cost-effective nursery scouting programs is underway at NC State. I am currently testing sampling plans for spider mites and lacebugs.
Many new pesticides are compatible with natural enemies, so biological control will become more important as part of nursery IPM programs. Studies in New Jersey have shown that the green lacewing predator can provide good lace bug control on azaleas when it is used in conjunction with insecticidal soap.

KEY PESTS: SOME EXAMPLES

Ambrosia beetles. These beetles bore into trees, causing loss of vigor and mortality. All species carry a fungus called ambrosia that they cultivate in their galleries as a food source. The most serious is the Asian ambrosia beetle, Xylosandrus crassiusculus, which also seems to introduce plant pathogens such as Fusarium sp., leading to rapid plant death. Ambrosia beetle activity is recognized by the frass plugs they push out as they excavate their galleries. Control is based on ethanol traps to correctly time pesticide applications; Astro is the most effective product. Fortunately ambrosia beetle numbers have been quite low this spring, possibly due to the cold weather last winter.
Other borers (e.g. flatheaded and clearwinged). Legislative changes will likely result in further restrictions on persistent, broad-spectrum pesticides commonly used to control borers. This means that accurate timing of pesticide applications will be critical. Pheromone traps for clearwinged borers (e.g. ash, dogwood, peachtree, and rhododendron borer) can be used to correctly time sprays. Alternative strategies, such as weakening borers with pesticides and then using nematodes to kill them, will come into use. Merit can be used for some important borer pests (e.g. it is effective for flatheaded appletree borers but not for clearwing borers) but must be applied well in advance of the problem for adequate uptake into the plant. Unless you are certain that you will have a problem, it may be difficult to justify this expense.

Spider mites. These mites are a common pest in North Carolina nurseries, where they can cause serious damage. Development of pesticide resistance is common in mites, so rotation of pesticides and use of alternate strategies such as biological control is important. One limitation to biological control has been the time required to deliver predators such as Phytoseiulus persimilis to large numbers of plants. Use of a mechanical dispenser or other dispersal aid can overcome this.

EMERGING PESTS
INSV/TSWV. These two plant viruses are already an important problem in greenhouse production, where they cause significant crop loss. TSWV infects over 900 plant species, including many herbaceous perennials. It is vectored by 5 species of thrips, 3 of which are common in North Carolina. The most common vector in ornamentals is the western flower thrips. Weeds are an important virus reservoir, in fact regular mowing of rows to prevent weed flowering can have a significant impact on thrips levels. The host range of INSV and its vector complex are less well-known, although both are probably large. The popularity of perennials and the common practice of overwintering plants makes it likely that these will become important nursery pests. Thrips are not a pest nursery growers typically watch for but this must change if these viruses are to be properly managed. It is also important to monitor thrips with yellow sticky cards.

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