Biological Control for Cut Flower Plugs

The interest in biological control options appears to be growing among cut flower growers. Besides the environmental concerns, the high cost of the new low-risk pesticides is making biological control options much more feasible.

Early in the season, most cut flower growers start plants in greenhouses where insects and mites can thrive. Biological control should start in there. If you are not starting plants in the greenhouse, you may be buying in unrooted cuttings, root cuttings or plugs to plant out in your fields.

If you were purchasing plants as cuttings or plugs, I would recommend starting by applying an entomopathgenic fungi and horticulture oil to take care of any pest you may be importing. Entomopathogenic fungi usually attach to the external body surface of insects or mites, in the form of microscopic spores called conidia. Under the right conditions of temperature and high humidity, these spores germinate, grow as hyphae, and colonize the insect’s cuticle. Then, the fungal cells proliferate in the host body cavity killing the insect or mite.

One of the readily available entomopathogenic fungi is sold under the name BotaniGard, and is used to control whitefly, thrips, aphids, and many other insects. It is based on the fungus, Beauveria bassiana strain GHA, and controls the most troublesome crop pests. Be sure to read the labels to make sure if any plants are listed as sensitive to either of these materials. A cut flower grower can mix up SuffOil-X and Beauveria bassiana (BotaniGard) in a large tank of water, and dip the leaves and stems in the solution. If other pesticides are to be added, do so after SuffOil-X has been thoroughly mixed. The oil is mixed at 1 gallon in 100 gallons of water. Check this rate on the oil’s label.  Add the BotaniGard after the oil is thoroughly agitated to a homogenous mix. The oil suffocates eggs, larvae, nymphs, and adult soft-bodied insects and mites. The oil should penetrate in the plant canopy. The oil is exempt from residue tolerances.

If thrips have been a problem in your plants started in the greenhouse, purchase the predaceous mite, Amblyseius cucumeris. These feed on the first instar larval stage of thrips. You can purchase these in a loose bran fill or in sachets that you hang in among the plants. The loose fill may work better if you have plants close together in small pots or growing trays.

If you have aphids, whiteflies, and thrips active in the plants started in the greenhouse, consider purchasing the little more expensive predator mite, Amblyseius swirskii. They feed on a wider range of insects.

To encourage the mites to disperse much more evenly onto the plant a cut flower grower can apply apple or cattail pollen to foliage with a mechanical blower. Then apply the predaceous mites, mixed in a bran mix, applied with a mechanical blower. The mite blower can be purchase from company such as Bio-Bee or Biobest, or if you are mechanical, build it yourself.

Cattail or apple pollen can be purchased from biological supply companies. Carol Glenister of IPM Labs, Locke New York, informs me that cattail pollen is blown over the crops at approx. 1 gram per 1000 sq. ft, which is an extremely light application. The pollen is pricey and a quality product created for this market is bright yellow and flowing. Bee collected pollen would not work because it is clumped.

She mentions that some growers collect their own pollen from local cattails in late June or early July, and freeze it for use on crops such as greenhouse-grown cut flowers and on poinsettias. It is used on poinsettia for feeding Amblyseius swirskii mites, which feed on whitefly and thrips. If you collect cattail pollen, it needs to be kept frozen or it begins to mold rapidly at room temperatures.

An interesting food source for feeding predaceous mites are decapsulated Artemia cysts, used as a supplement to enhance the establishment and activity of predatory insects and mites in greenhouse crops. Bio-Bee Company has these eggs available to feed a range of generalist predators. Artemia cysts are very nutrient-rich and boost fecundity (fertility and egg laying) and longevity of predaceous mites. They also have some logistical advantages over the other types of supplemental food in that they can persist in the crop for several weeks. The Bio-Bee web sites suggest if these eggs are keep in sealed containers maintained at 50F or less they can be kept 4-6 weeks. Some have suggested that if the eggs are frozen they can be stored for at least three years.

Artemia cysts enhance the establishment and performance of generalists such as predatory bugs (e.g. Orius), mirids (e.g. Macrolophus), and mites (e.g. swirskii, limonicus). Orius (minute pirate bugs) are very good for biological control of thrips—all life stages.

The Artemia cysts are sprinkled or blown into the crop to feed the predators, which are then released before the pests arrive. The goal is to establish the predators in the crop, so that once pests such as thrips or spider mites appear, there is a strong defense of predaceous mites in place to combat them. The supplement can be reapplied throughout the crop cycle to support predators when pest numbers are low.

We are still in the early stages of testing out some of this biological control in outdoor environments. Through years of experience and field trials, we established these techniques work well in greenhouse. For the last two years we have been testing out a combination of low-risk pesticides combined with biological control releases. We will be publishing the results of these trials in summer issues of the national magazine GrowerTalks. Stay tuned.

Stanton Gill

Extension Specialist

Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]