Wipe it Out?

Ever wish you could wipe out all of the bad insects in your cut flowers? Well, you can’t, so just get over it.  The best that you can hope for is to keep them at levels at which you can still harvest some flowers with minimal damage. How do you do this? Well, if you get to know the pests, then you can destroy them. We have made it easy for you because in September of 2006 we published the second edition of Pests and Diseases of Herbaceous Perennials: The Biological Approach, from Ball Publishing Company.  Now you can flip through thousands of pictures of your favorite insects, find out all of their secrets, and learn how to wipe them out—or at least suppress them for a while.
One of the most popular groups of insecticides are available for cut flower growers is systemic insecticides.  Probably most common is acephate (Orthene), which has been around since the 1970s.  The EPA reports that acephate is the systemic insecticide most widely used by professionals and home gardeners in the Unites States.  It is relatively cheap and it controls a wide range of pests in cut flower operations including aphids, thrips, caterpillars, whiteflies, harlequin bugs and leaf-feeding beetles.  It is labeled for use only as foliar spray and gives control for 7–14 days for most pests.  We have conducted trials with of acephate applied to root zones and it gave several weeks of control.  One company has a labeled formulation of acephate that can be applied to soilless substrate in nurseries, but it is rather limited for what it can safely be used on. It is not labeled for soil applications in field situations because it is so water soluble  it would move in many soils and could possibly end up in water supplies. So, field growers are basically limited to foliar applications.

How Systemic Insecticides Kill Insects

Systemic insecticides available to cut flower growers are associated with two modes of action: nicotinic acetylcholine receptor disruptors, and selective feeding blockers.  The neonicotinoid-based insecticides kill target insect pests by acting on the central nervous system, causing irreversible blockage of the postsynaptic nicotinergic acetylcholine receptors.  These systemic insecticides disrupt nerve transmission in insects causing uncontrolled firing of nerves. This results in rapid pulses from the steady influx of sodium, leading to hyperexcitation, convulsions, paralysis and death. Sounds gruesome, but just how attached to the insects that damage your cut flowers are you?
What are some of these neonicotinoids that are on the market for controlling pests? There are presently five neonicotinoids out there : imidacloprid (Marathon), thiamethoxam (Flagship), dinotefuran (Safari), clothianidan (Celero), and acetamiprid (Tristar). Some are labeled for foliar applications, some are labeled for soil applications and some have labels for both.  Systemic insecticides applied as soil applications take a little longer to be carried through the plant compared to foliar applications, but they generally remain toxic to pests for longer periods of time.                 

One of the main concerns with using systemic insecticides having a single or site-specific mode of activity, such as the neonicotinoids, is that the selection pressure placed on insect pests from continual use of these systemic insecticides may result in the development of resistant genotypes or biotypes.  Most cut flower growers use these products once or twice during a growing season, whereas greenhouse growers have longer periods of pest activity and often make multiple applications, increasing the chance of resistance.  with increased chance of resistance developing.
Some systemic insecticides are classified as selective feeding blockers, which have a broad or physical mode of activity. These products kill insects by interfering with neural regulation of fluid up-take, thus blocking their stylet (feeding tube), which prevents them from withdrawing plant fluids. As a result, the insects starve to death. This mode of action is less susceptible to insects developing resistance—in the short term. However, continued use of this mode of action for long periods of time may eventually reduce the effectiveness of these systemic insecticides.

Making the Most Effective Applications of Systemic Insecticides

Systemic insecticides must be applied to the root zone when plants are actively growing and have an extensive, well-established root system, in order to enhance the uptake of the active ingredient through the vascular tissues.  Applying systemic insecticides on warm, sunny days will also lead to increased movement of the active ingredient through the transpiration stream.  In contrast, uptake is inhibited when plants don’t have well-established root systems.  In addition, high humidity and low light conditions can lead to reduced uptake of systemic insecticides.  Any delayed movement of the active ingredient may result in the material taking longer to kill insect pests. Systemic insecticides are also more effective when plants are herbaceous rather than woody, particularly on sucking insects such as aphids.
Systemic insecticides, when applied to the growing medium, need to be used preventatively in order to control phloem-feeding insects such as whiteflies, aphids, and mealybugs. If systemic insecticides are applied after insect pest populations are already established on plants, this may delay control, resulting in insect pests causing damage before ingesting enough active ingredient to kill them.

Want More Information?

Buy our book and start reading! Meanwhile, if you have insect questions you can call me at (410) 868-9400 or email me 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]