Utah Pests News Spring 2009

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Imidacloprid for Insect Control

In the mid 1980s, Bayer CropScience patented a new chemical for insect control—imidacloprid (IC).  Registered for use in the United States in 1994, this chemical was the first in a new group of insecticides known as the neonicotinoids, and is currently considered the most widely used insecticide in the world.  Today, neonicotinoids (mode of action group 4a; click here for MOA descriptions) includes active ingredients such as acetamiprid, clothianidin, dinotefuran, nitenpyram, thiacloprid, and thiamethoxam.  There are over 250 IC-containing products available in Utah.

Imidacloprid is registered on over 140 crops for a variety of pests. The following are controlled by Merit 75 WP:
European crane fly
*mole crickets
annual bluegrass weevil
flatheaded borers
Oriental beetle
green june beetle
pine tip moth
asiatic garden beetles
Japanese beetle
lace bugs
black vine weevil
leaf beetles
*sod webworm
*chinch bug
soft scales
emerald ash borer
masked chafers
white grubs
European chafer
Application methods to control insects in this list vary by crop and situation. Please carefully read the label before applying. (*suppression only)

Imidacloprid is not a true systemic insecticide because it not translocated throughout all plant tissue, however it may diffuse partially into the phloem.  When applied as a soil drench/injection, trunk injection, or seed treatment, it is transported throughout the water-carrying vessels (xylem), providing “systemic” protection.  When IC is applied as a foliar spray, it may be absorbed into the leaves via “translaminar flow.”  Any susceptible insects feeding on foliage or phloem tissues will be killed as a result of contact or ingestion with IC.   Imidacloprid kills insects by causing rapid firing of nerves, leading to paralysis and death.

Apply Imidacloprid Safely and Effectively..
    An IC product can be applied with, or after a curative insecticide for long-term pest control. (Check the product label for compatibility.)  
    Do not mix IC with any products containing Boron.  
    Imidacloprid can be applied with fertilizer to promote faster uptake and translocation.  
    For insect control in woody plants, fall and early spring are good times to apply soil drenches/injections. These applications are best followed by irrigation, and should not be applied to waterlogged soil.  
    Because IC is translocated quickly in turf, it is best to apply during the egg-laying period of the target pest.  
    Imidacloprid is highly toxic to bees, so do not apply or allow drift on blooming plants.

When used as a soil drench/injection or trunk injection, imidacloprid can remain active from a few months to a year.   It is a good choice for IPM programs because it targets foliar- and phloem-feeding pests while preserving predatory insects.  Because this type of application can take days (turf) to months (large trees) for the chemical to translocate, it may take a while to see results.  If pests are causing major damage and immediate control is needed, consider applying fast-acting insecticides like spinosad, horticultural oil, synthetic pyrethroids, etc.  The insecticide you choose will depend on your target pest and location, and the timing will depend on the pest life cycle.  Any unknown pest should be sent to the Utah Plant Pest Diagnostic Lab for identification.  Many common Utah pests are described in Extension fact sheets.

As with any insecticide, IC is a chemical that enters the environment.  While it has lower toxicity levels than many broad-spectrum insecticides, it is capable of killing or giving sub-lethal doses to many non-target insects, including bees, parasitic wasps, birds, and mammals.  This chemical, when used as a seed treatment, has been implicated (but not proven) in contributing to widespread honey bee death in Europe.  It is banned in France, Italy, Germany, and Slovenia as a seed treatment on such crops as sunflower, rapeseed, and sweet corn.   It is highly toxic to fish and aquatic invertebrates.  Because of its frequent use, insect resistance to IC is building in some systems like Colorado potato beetle in Michigan, and the greenhouse whitefly in Europe.   Make sure to rotate insecticides that have different modes of action (see the spring 2008 Utah Pests newsletter for more information on preventing resistance).  Additionally, IC has been shown to increase spider mite fecundity (number of eggs produced).   For more details on the potential side effects of IC click here.  An article containing counter-arguments may be found here.

The use of IC should be secondary to cultural and mechanical practices of maintaining a healthy landscape, which can reduce the amount of chemicals needed by over 90%.  Use proper monitoring/scouting techniques to survey for pests before damage occurs, and only apply IC if there is current, or imminent damage.  Once pests are under control, discontinue the use of any insecticide and resume non-chemical methods of pest management.  As always, carefully read and follow the application instructions on the product label.

-Ryan Davis, Arthropod Diagnostician