Using Good Fungus for Insect Control in Cut Flowers

It is summer and your cut flowers are looking great. Unfortunately, our buddies, the bugs of the world, are highly focused on and enthralled with your beautiful blooms.

As cut flower growers you want perfect flowers with minimal pest damage. The question is how to deal with major plant-feeding insects without using harsh, broad-spectrum, and expensive insecticides.

The answer may lie in use of beneficial fungi called entomopathogenic fungi. Over the last 18 years we have conducted many field trials with two, Metarhizium anisopliae and Beauveria bassiana. Both are readily available from commercial sources.

The one we have had the most experience with is Beauveria bassiana, sold by Bioworks under the name BotaniGard as a liquid or wettable powder formulation. BotaniGard contains conidia of Beauveria bassiana combined with a wetting agent. The conidia are mixed in water and applied as a fine mist onto the insect. When the conidia make contact with the insect, they germinate, producing hyphal growth that penetrates the insect resulting in its death.

In Canada, many growers dunk trays or flats of susceptible plants in a water trough containing the BotaniGard mixture, submerging the plants for 15-20 seconds. This coats the foliage, and any insect present. It is effective in dealing with aphids, thrips, and whitefly. BotaniGard now has labeled instruction for dunking plants using this methods. Several growers in Maryland use this practice to reduce insects on young plants.

Thrips. Actually a Single Noun

Thrips are one of the most important summer problems for cut flower growers. Populations can build quickly if not controlled early; spraying should begin at the first sign of thrips activity. We have had a fair amount of success using Beauveria bassiana applied as a fine mist, and have achieved excellent thrips control in the greenhouse with Metarhizium anisoplia.

With both of these entomopathogenic fungi, the thrips need to be hit by the spray or come in contact with spores on the leaf surface. In our trial we generally use a backpack motorized mist sprayer. Its fine mist is more likely to allow the conidia to make direct contact with the insects, especially with thrips, which tend to be rather cryptic. Aphids tend to feed out in the open so it is easier to make contact with them. For whiteflies you need to make sure the mist lifts the foliage to make contact with the sessile stage on the underside of the leaf.

Western flower thrips tend to congregate in flowers or clusters of flowers, so spray should be concentrated there and on the upper foliage. If the plant is not flowering, Western flower thrips may be found in the leaf axils. They no longer have a migratory path, and effective spray coverage becomes even more critical. In our trial we’ve had our best success in greenhouse systems, and are just beginning to conduct field trials. Applications during more humid parts of the summer should increase the efficacy. I have had conversations with Dr. Chris Hayes of BioWorks, which is effectively using BotaniGard on outdoor field crops and some fruit crops in Mexico.

For thrips, whitefly, and aphids, the label rate is one quart of BotaniGard in 100 gallons of water. For thrips I suggest applying every 5 to 7 days during high activity. If you are going after aphids the intervals must be tightened up to every 3 to 4 days. Aphids grow rapidly in early summer and shed their skins quickly. If you apply the conidia to the exoskeleton the aphid may shed its exoskeleton before the fungus effectively penetrates its body. For whitefly a 7-day interval should be adequate.

BotaniGard is compatible with most beneficial insect programs. When sprayed according to label directions, BotaniGard will not reduce populations of most predatory mites such as Amblyseius cucumeris used for biological thrips control. Apply when bumblebees are not foraging.

The Metarhizium anisopliae is good for thrips, whitefly, and spider mite control. I have not had as much success with this material with aphids. It is sold under the name Met-52. This is a liquid bioinsecticide labeled for use in the United State and Canada. It is a naturally-occurring fungus, meaning it has not been genetically modified.

Keep in mind that Metarhizium anisopliae does impact both plant-feeding and predatory mites. If you are using predatory mite release for thrips control, this is not the best choice of materials for you. Met-52 has range of rates on its label, from 8 to 32 ounces in 100 gallons of water for foliar applications.

I’ll see you in September in Raleigh, North Carolina. Take me out to dinner and we can chat about your bugs.

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]