MSU Extension Floriculture & Greenhouse Crop Production

Starting and staying clean(er)

Prevention and sanitation are critical in reducing the risk of insect, mite, and disease outbreaks in the greenhouse. Incoming plant material, even if it appears uninfested, is a common way that pests and pathogens are introduced into floriculture production facilities. Ideally, growers should segregate all incoming plugs and liners (particularly vegetatively propagated material) into a clean quarantine area where the new plants can be regularly monitored and, if necessary, treated for an infestation before moving them into the main production area. Prior to transplanting, some growers proactively treat specific kinds of plants for common pests while they are still in plug trays, especially if they intend to finish them in overhead hanging baskets.

Older plants can become reservoirs for pests and pathogens. Operations that maintain stock plants for cuttings should strive to keep insect and mite numbers on these plants as low as possible. Stock plants often develop a dense canopy, which can reduce the penetration and efficacy of spray applications. In such cases, an integrated approach that includes beneficial organisms could prove to be the most effective and resource-efficient option over time.

Weeds can also serve as sources of insect pests and diseases. Removing broadleaf weeds from the greenhouse perimeter and indoor production areas will help the operation stay cleaner. Using grass or gravel to cover the area directly outside the range and installing weed barrier underneath benches are time-tested methods for keeping broadleaf weed pressure to a minimum.

Cutting dips

Research has shown that any plant material entering the greenhouse is likely to have a small number of pests. Because of this, some floriculture growers dip unrooted cuttings and plugs into reduced-risk pesticides to help lower the number of these hitchhikers. This technique was evaluated by researchers at Canada’s Vineland Research & Innovation Centre and has since been adopted by many growers in Ontario. In the United States, there are currently several commercially available products on the market that include labelled uses for dipping: 

Note: Some plants may be sensitive to these treatments (see Phytotoxicity)

Regulatory considerations:

Cutting dips are considered pesticide applications. In practical terms, this means:

• Applicators are required to wear all appropriate label-required personal protective equipment (PPE) when performing cutting dips.
• Employees involved with sticking cuttings immediately following treatment should be trained as Worker Protection Standard (WPS) handlers and be provided PPE as specified on the product label.
• All employees are required to follow label-required restricted-entry interval (REI) specifications for treated areas.

Note that some of these products (*) qualify for exemption from EPA registration under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and may not carry WPS or Agricultural Use requirement statements. Precautions and Restrictions typically located within the Agricultural Use section, such as those pertaining to PPE and REI, might be detailed under the label's Precautionary Statements.

For more information on WPS training requirements or using cutting dips to treat vegetative cuttings, contact a member of the Michigan State University Extension floriculture team (canr.msu.edu/floriculture/experts).

Scouting is important

Managing a small population of pests is much easier than managing a large one, particularly when the plant canopy is dense and flowers are present. Regular scouting/monitoring can help growers detect infestations early and prevent damaging outbreaks. Two useful tools for scouting are colored sticky cards and a hand lens. Sticky cards help detect flying/jumping insects in the crop and are particularly useful for monitoring thrips populations. Place one card at canopy level every 2000-4000 ft² or at least one per house. Place cards away from where flying biological control agents are being released as these may become trapped as well. Physical inspections of foliage and flowers are important for detecting non-flying pests such as aphids and mites. A hand lens (minimum 10x, suggested 15 – 20X) is used to examine tiny insects and mites and can help confirm pest identification. Digital magnifiers attached to laptop computers or smart phones are also a viable option.

Neonicotinoids

Neonicotinoids are class of insecticides that grew in popularity due to their relatively low mammalian toxicity and ability to move systemically throughout the plant. All neonicotinoid products are in the Mode of Action (MoA) group 4A (see below). Growers with buyers that require neonicotinoid-free plants should look to systemic insecticides in other chemical classes or MoA groups, such as Altus (group 4D), Mainspring (group 28), and Kontos (group 23).

Pyrethroids

Pyrethroids are a class of insecticides with a molecular structure similar to pyrethrins, which are natural compounds produced by some Chrysanthemum species. Like neonicotinoids, pyrethroids are used extensively throughout the world because of their broad-spectrum insecticidal activity and negligible toxicity to humans and other mammals. Due to documented resistance issues in all major greenhouse floriculture pest groups and incompatibility with many biological control agents, we no longer recommend pyrethroids as a primary insect management tool. Nevertheless, they still provide some usefulness in rotation and, with few exceptions, have an established record of plant safety (low risk for phytotoxicity). All pyrethroids and pyrethrin products are in the MoA Group 3A (see below).

Resistance Management

Repeated use of products with the same Mode of Action over an extended period of time increases the likelihood that pest populations will become less susceptible to those products (see pyrethroids). To delay or prevent pesticide resistance, avoid using insecticides unless it is necessary. For persistent pest populations on long-term crops (e.g. foliage), consider a rotation schedule of products with a minimum of 3 (more is better) different MoA groups. The MoA class is clearly noted on most labels and also published by the Insecticide Resistance Action Committee (IRAC) (irac-online.org/mode-of-action).

Phytotoxicity

Manufacturers typically test their products on a broad range of plants. They cannot, however, test every ornamental species, variety, tank mix combination, and situation.

Before applying a product to a crop for the first time, you should:

• Consult the label for crop tolerance considerations.
• Test the product at the desired rate on a small number of plants and observe for possible sensitivity over a week or two. Be sure plants are well-watered and not under moisture stress when treated.

If mixing the product with adjuvants or other products for the first time, you should:

• Consult for label for tank-mix compatibility notes.
• Test the product at the desired rate on a small number of plants as described above.

Insecticide products for key greenhouse pests

MoA = Mode of Action
REI = Restricted Entry Interval
UNM = Non-specific mechanical and physical disruptors
¹ Other azadirachtin products include: AzaGuard, Azatrol, AzaSol, Ornazin.
² In research trials, foliar spray applications of Safari, Flagship, and Kontos were as effective as drenches at controlling mealybugs. Adding a spreader adjuvant such as CapSil or Silwet improved efficacy.
** Restricted entry intervals vary across azadirachtin products. Please consult the label.

We thank Dan Gilrein of Cornell University for his review of this document.

The information presented here is for educational purposes only. Reference to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned.