Going Systemic on Insects

Systemic insecticides offer several advantages to specialty cut flower growers over many contact pesticides. Generally, once systemic insecticides are inside plants they have less of a chance of impacting beneficial predators. Secondly, since systemics are not as susceptible to ultraviolet light degradation and breakdown by organisms on plant surfaces, they control pests longer. Lastly, and most importantly, plants treated with systemic insecticides are generally less harmful to workers and customers compared to plants receiving spray applications of contact insecticides.

These treatments may not be appropriate for all pests but will kill many sucking insects that attack specialty cut flowers; the insecticide moves up the plant via the transpiration stream, killing insects that feed within the phloem or food-conducting tissues, such as aphids, plant bugs, stink bugs and whiteflies. As an insect feeds, it withdraws a lethal dose of the insecticide and is killed.

Most systemic insecticides don’t provide good spider mite control. The two-spotted spider mite (Tetranychus urticae) does not feed within the vascular tissue (xylem and phloem) so they don’t pick up the insecticide. Spider mites feed primarily on leaf undersides within plant cells, damaging the spongy mesophyll, palisade parenchyma, and chloroplasts with their stylet-like mouthparts. One systemic miticide on the market, spiromesifen, (Forbid for outdoor use, Judo for greenhouse use), controls controls spider mites, broad mites and whiteflies, but some argue that it is not a “true systemic” since it is sprayed onto foliage and cannot be applied to the soil for root uptake.

Growers have used neonicotinoids for the last fifteen years, with imidacloprid (many brand names since the patent expired) the first, followed by acetamiprid (TriStar), dinoetefuran (Safari), and thiamethoxam (Flagship). Whether it is imidacloprid or one of the other neonicotinoids, these systemic insecticides act as nicotinic acetylcholine receptor disruptors.  These act on the central nervous system, causing irreversible blockage of the postsynaptic nicotinergic acetylcholine receptors. This is exciting stuff and I am sure you are thrilled to learn this information. The bottom line is they disrupt nerve transmission in insects, causing uncontrolled firing of nerves leading to insect going into convulsions, followed by paralysis and finally, death.

Since imidacloprid went off trademark, several companies jumped in, offering many generic brands of it, greatly reducing the price. End result: more thrifty cut flower growers starting using imidacloprid. Remember that if you start using one of the systemic insecticides in the neonicotinoid group, you want to rotate with another class of chemistry during the season to slow down development of resistance.

Systemic insecticides labeled for soil application will provide the longest time of insect control. However, they may take longer to be distributed throughout the plant, especially water-insoluble insecticides such as imidacloprid. Systemic insecticides applied to plant foliage work more quickly, but provide shorter residual activity. Generally, a soil application gives you the biggest bang for the longest time.

Our team at the University of Maryland Extension (Karen Rane, Andrew Ristvey, Chuck Schuster and Stanton Gill), and faculty at VPI (Joyce Latimer) and North Carolina State University Extension (Brian Whipker) have teamed up over the last two years to develop Total Plant Management for Greenhouse Management with Emphasis on IPM and Nutrient Management.

Karen Rane’s plant pathology chapter focuses on disease control options which can be applied to cut flowers. Andrew Ristvey and Chuck Schuster provide information on fertility and water management strategies. My section covers greenhouse insect control. Print and electronic copies will be available; contact Stanton Gill at [email protected].

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]