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Systemic, Local Systemic, or Translaminar Insecticides: What's the Difference?

November 27, 2002

Many insecticides kill pests by contact activity. Insect or mite pests are either killed from direct contact during spray applications or by coming into contact with wet residues when moving around upon plant surfaces. Contact insecticides generally provide quick knockdown of target pests.

Many insecticides from the older chemical classes –including the organophosphates (that is, chlorpyri-fos and diazinon), carbamates (methiocarb), and pyrethroids (bifenthrin, cyfluthrin, fluvalinate, fen-propathrin, and permethrin) have contact activity. However, some insecticides have either systemic or translaminar (local) properties. Older systemic insecticides/miticides that are no longer available include aldicarb (Temik) and oxamyl (Vydate). Currently available systemic insecticides include imidacloprid (Marathon, Merit), acephate (Pinpoint), and pymetrozine (Endeavor).

In addition to insecticides, several fungicides are available with systemic activity, including mefenox-am (Subdue Maxx) and fosetyl-aluminum (Aliette). In fact, Aliette is the only fungicide available that moves both up and down the plant’s vascular system. However, this article primarily concentrates on the action and use of systemic insecticides.

Systemic insecticides are those in which the active ingredient is taken up, primarily by plant roots, and transported (translocated) to locations throughout the plant, such as growing points, where it can affect plant-feeding pests. Systemics move within the vascular tissues, either through the xylem (water-conducting tissue) or the phloem (food-conducting tissue) depending on the characteristics of the material. However, most systemic insecticides move up the plant (water-conducting tissue) with the transpiration stream. Systemic insecticides are most effective on insects with piercing—sucking mouthparts, such as aphids, whiteflies, mealybugs, and soft scales, because these insects feed within the vascular plant tissues. Most of the newer systemic insecticides have minimal if any activity on spider mites because spider mites remove plant chlorophyll (green pigment) and don’t feed within the vascular tissues.

Systemic insecticides may be applied directly to the growing medium, soil; or they can be sprayed onto plant leaves. Systemics applied to the growing medium and taken up by plant roots may in some cases provide up to 12 weeks of residual activity. However, they may take longer to be distributed throughout the plant. In contrast, systemics applied to plant foliage may provide up to 2 to 4 weeks of resid-ual activity. Nonetheless, foliar-applied systemics provide quicker kill of target pests. In either case, systemics provide the plant with long-term protection from pest injury.

The water solubility of systemic insecticides deter-mines their movement within plants. Systemic insecti-cides, in general, are very water soluble (an exception is imidacloprid), which allows them to be taken up by plant roots or leaves. In addition, plants do not readily metabolize them. However, due to their high water solubility, they are subject to leaching and may potentially contaminate groundwater.

Systemic insecticides should be applied when plants have an extensive, well-established root system and when they are actively growing. This leads to greater uptake of the active ingredient through the vascular tissues. Applying systemic insecticides dur-ing warm, sunny days also leads to increased uptake of the active ingredient through the transpiration stream. In contrast, uptake is less in plants without well-established root systems. Also, high humidity and low light can lead to reduced uptake of systemic insecticides. Any delayed uptake of the active ingredient may result in the material’s taking longer to kill insect pests. Systemics are also more effective when plants are herbaceous rather than woody, particularly on stem-feeding insects such as aphids.

Some insecticides/miticides have translaminar, or local, systemic activity. These materials penetrate leaf tissues and form a reservoir of active ingredient within the leaf. This provides residual activity against certain foliar-feeding insects and mites. Insecticides/miticides with translaminar properties include aba-mectin (Avid), pyriproxyfen (Distance), chlorfenapyr (Pylon), spinosad (Conserve), and acephate (Orthene). In general, these types of materials are active against spider mites and/or leafminers. Because the active ingredient can move through plant tissues (that is, leaves), thorough spray coverage is less critical when using these materials to control spider mites, which normally feed on leaf undersides.

The benefits of using systemic insecticides include (1) plants are continuously protected throughout most of the growing season without the need for repeat applications, (2) these insecticides are not sus-ceptible to ultraviolet light degradation or "wash off" during watering, (3) there is less unsightly residue on foliage or flowers, and (4) harmful effects to workers and customers are minimal. A problem associated with systemic insecticides is that many have a single, or site-specific, mode of activity, which may lead to resistance. The selection pressure placed on pests from the continual use of systemic insecticides may result in the development of resistant genotypes. An exception to this situation is the insecticide Endeavor (pymetrozine), which has a broad, or physical mode, of activity. Endeavor kills aphids and whiteflies by blocking their stylet (feeding tube), thus preventing them from feeding. As a result, the insects starve.

Although systemic insecticides are generally considered less harmful to natural enemies, research has shown at specific predators such as Orius spp. that supplemental feed on plants may take up enough active ingredient to kill themselves.

Systemic insecticides can provide long-term con-trol of insect pests without having to rely on regular spray applications. However, it is important to use proper insecticide stewardship to minimize the risk of insect populations’ developing resistance to currently available systemic materials.

Author: Raymond A. Cloyd


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