Aphids

Aphids and other soft-bodied insects are good candidates for control by systemic insecticides.

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Gardeners use systemic pesticides quite often, but what exactly is a systemic pesticide?

These are insecticides and fungicides that are taken in or absorbed by the plant, then moved throughout its trunk, branches, foliage and growing points. This distinguishes a systemic pesticide from a contact pesticide, which stays on the leaf or branch surface it is applied to and does not move into plant tissues.

Systemic products move in the plant’s vascular system, either through the water-conducting xylem tissue or the food-conducting phloem tissues, or both. Once inside the plant, the chemical may also move back and forth from the xylem to the phloem, and vice versa, through passive diffusion.

Most systemic insecticides move upward in the plant via the xylem, so a product applied as soil granules will be dissolved by water, picked up by the plant’s roots and moved upward to the top growth. The same product applied as a foliar spray also will move upward from the point of application, with little downward movement leaving the lower parts of the plant and its roots unprotected. This may be an important consideration, depending on the type of insect or disease being controlled.

Systemic insecticides kill insects when they ingest a lethal concentration during feeding. Systemic fungicides form a barrier on and within the plant, killing fungal spores and fungal roots, called hyphae, as they germinate and begin to grow.

Systemic products have several benefits. First, they provide continuous plant protection for a specific length of time. The residual period, or length of protection, varies for each product based on the amount of chemical applied and the concentration of the active ingredient.

Contact pesticides sprayed on plant foliage naturally lose their effectiveness as they are broken down by sunlight; this is less of a problem with systemic products since the active chemical moves into the plant after application. Similarly, rainfall after a pesticide application is less of a concern, since maintaining a “barrier” of pesticide on the plant is not critical with systemic products as it is with contact pesticides. Systemic products also have less chemical residue on the foliage, flowers and branches to detract from the plant’s beauty.

Systemic products are commonly applied to plants in four ways:

* Soil application of granules

* Liquid soil application, as known as a soil drench

* Spray application to trunk, branches or foliage, and

* Trunk injection.

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For plants to take up systemic products through their root system they must have a well-developed root system and be actively growing. Due to the amount of time needed to reach a protective concentration in the plant, systemic products should be applied preventatively, however, their use is only justified on high value plants with a known history of insect or disease infestation.

Spray application of systemic fungicides are most effective when made during humid, cloudy weather when soil is moist. Leaf cuticle, the waxy outer layer, has swelled and is more open, allowing the fungicide to penetrate easier. Fungicide has a more difficult time penetrating the outer cuticle during periods of extended hot dry conditions.

Common systemic pesticides available to home gardeners include the following, although this is not an all-inclusive list:

* Insecticides -- acephate (Orthene) and imidacloprid (Merit and many other formulations).

* Fungicides -- azoxystrobin (Heritage), myclobutanil (Spectracide Immunox), propiconazole (Banner Maxx), triadimefon (Bayleton).

Read and follow all label directions to get the most effective control of your insect and disease problems, paying particular attention to the rate and method of application and reapplication interval.

Sarah Browning is an extension educator with Nebraska Extension and can be reached at 402-441-7180 or sbrowning2@unl.edu.

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