Managing Insect Pests in Cut Flowers Using Biologically Based Insecticides

Japanese beetles on a zinnia.

Growing specialty cut flowers outdoors can be quite challenging because of the various insect pests that thrive in the Mid-Atlantic region.

While biological control options exist for specialty cut flowers, growers must realize these tools must be deployed as strategically as chemical pesticides to achieve good control or management.

Natural pyrethrums are often the first product that organic growers reach for to combat insect pests. While natural pyrethrum insecticides are a great tool to have in the organic tool chest, they often prove to be ineffective in controlling some aphid species and some beetle pests.

Natural pyrethrum insecticides have a very short residual and will provide rapid knockdown, some mortality and some repellency when used on specialty cut flowers. If natural pyrethrum insecticides are to be used successfully, a grower often must be prepared to make one or more insecticide applications per week, unless directed otherwise by the pesticide label.

The next bio-based product in the organic tool chest is the insecticide azadirachtin, which is derived from the neem tree. Azadirachtin works as an insect growth regulator, antifeedant, oviposition deterrent and repellent.

A spotted cucumber beetle, which will chew holes in flower petals.

Azadirachtin products like Aza-Direct or Azatin O (OMRI listed) are labeled for controlling aphids, beetles, stink bugs, tarnished plant bugs, caterpillars, mites and thrips.

Insecticides containing azadirachtin are toxic to honeybees, so cut flower growers should consider applying this insecticide in the evening, at night or in the early morning hours to minimize the risk of contact to foraging honeybees.

Spinosad, which is derived from a soil bacterium, can be found in the OMRI-listed insecticide Entrust SC. Entrust SC is labeled for controlling caterpillars, thrips and leafminers.

Spinosad is very toxic to honeybees and should be applied to floral crops when bees are not actively foraging.

Western flower thrips are a flower grower’s worst nightmare because their feeding can cause developing flower buds to blast (abort). Western flower thrips are also the primary vector for impatiens necrotic spot virus or INSV.

A thrips, which is a common pest to cut flowers.

INSV can infect over 600 different plant species including annual and perennial cut flowers. Infected cut flowers should be removed from the planting as soon as confirmation from an accredited diagnostic laboratory is received.

Spinosad containing products like Entrust SC are often the first line of defense against thrips in the cut flower field.

Venerate XC (derived from heat-killed Burkholderia spp. strain A396) is an OMRI-listed insecticide that can be used by cut flower growers to manage aphids, thrips, tarnished plant bugs, whiteflies and a variety of caterpillar pests. Venerate works as both a contact and stomach poison and is reported to have some impact on an insect’s exoskeleton and molting process.

The insecticide, Venerate, also should not be applied to flowering plants when bees are actively foraging.

To discuss bio-based pest management for a cut flower operation, contact Penn State Extension educator Thomas Ford at [email protected] or 814-472-7986.

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