Systemic pesticides have long been available for commercial use by growers and on a limited basis for the homeowner… let’s take a quick look at systemics.
Simply put… chemicals absorbed by a plant, transport in active form throughout its tissues, noninjurious to the plant and able to ward off invading organisms for an indefinite period.
A limited number of such compounds have been introduced commercially following intensive screening by research laboratories.
What is a Systemic Pesticide?
Systemics are chemicals absorbed into the system of a plant which renders its parts, the roots, stems and leaves poisonous to invading organisms. Some systemics remain unchanged in the plant, others are chemically altered before they become active poisons. A plant treated with a systemic is no longer merely a target for chemicals but it becomes a more able participant in setting up conditions unfavorable to invaders.
How do Systemics Enter Plants?
The chemical reaches the internal tissues by first passing through certain of the millions of microscopic cells forming the surface of leaves, stems, roots or seeds.
How do Systemics Move within the Plant?
Water and food-conducting tissues are the usual pathways through which these chemicals move over long distances.
For example, if the soil around the roots is drenched with a systemic compound, the chemical will appear in the leaves or fruits. The reverse direction of movement also occurs.
Some systemics tend to move upward from the point of application accumulating in leaf margins, growing tips and storage organs. Others collect in underground parts.
The image illustrates typical leaf injury that may result from using too much. Plants differ widely in their response to systemic chemicals. Compounds absorbed through the seed coat may kill organisms invading the seed or seedling plant.
How do these Compounds Work?
These foreign chemicals absorbed by a plant may greatly influence its balance of physiological processes.
The effect may be to kill or discourage the pest as it begins to feed or enter the plant, or it may rid the plant of an established pest, or it may counteract poisons produced by invading fungi or bacteria, or it may increase the natural resistance of the plant or retard the visible symptoms of disease.
Do Systemics Remain Active Indefinitely?
The effectiveness generally decreases the longer the chemical is in the plant. This may be caused by dilution of the systemic within the growing plant, or by a breakdown of the chemical by physiological processes within the plant, or by accumulation or congregating of the compound in certain restricted parts of the plant.
This means that the first contact of the plant with the systemic must provide the toxic level required to protect the plant from injury, or the chemical must be renewed as the plant develops.
How are these Chemicals Applied?
The most common methods are spraying the leaves, drenching the soil, and treating the seeds. Chemicals have also been injected into the trunk or stem of plants, or applied as a paste to the outside.
Insect and Mite Problems are being Solved by Systemics
The first use of systemic insecticides was impractical. Sodium fluoroacetate absorbed by bean plants killed insects which fed on the leaves but also left the beans too poisonous to be used as food. Entomologists observed that aphids did not infest wheat grown on soils high in selenium. But this chemical was too toxic for safety at the levels required for insect control.
In the last 30 years a new wide range of chemicals has been found and field-tested in control of plant-feeding insects.
In addition to killing pest species these systemics, generally are noninjurious to beneficial insect predators and parasites. By using these compounds full advantage of biological insect control may be realized.
What types of Diseases may be controlled by Systemics?
In recent years systemic fungicides have been used successfully to combat diseases of fungus, bacterial and virus origin as well as some deficiency troubles.
Fungus diseases controlled, or temporarily checked, include oak wilt, fusarium and verticillium wilts of certain plants, rhizoctonia root rots, grape black rot, early blight of tomato, bleeding canker of various trees, damping-off of seedling plants, and some diseases of turf.
Bacterial diseases which have been controlled using streptomycin preparations include halo blight and common blight of beans, fire blight of fruit trees, walnut blight, bacterial spot of tomato and pepper, soft rot and bacterial wilt of chrysanthemum, bacterial blight of celery and soft rot of philodendron. Others are being added every month.
Potentially the greatest use may be for root rots, wilts and viruses not successfully controlled at present. Several chemicals have prevented the development of these diseases but are not being widely used because of cost, difficulty in application or not giving protection long enough for practical control.
The commonly used organic fungicides maneb, captan, and others have limited systemic activity. The antibiotics, produced by living microorganisms like streptomycin are effective for certain diseases of fungus or bacterial origin.
What are Future Prospects?
Despite problems and the “Green Movement”, future research should whittle down what appear to be insurmountable obstacles.
When we know more about the processes of absorption, movement and storage of chemicals in tissues, the reactions of systemic compounds which result in plant protection without injury, the doors which now guard the wide-spread use of systemics may be unlocked.
Let’s be patient and wait for scientists to do their research. This should be well worth waiting for.
Pesticides and Brain Cancer
Over at www.insidermedicine.ca there’s a story about pesticides being linked to brain cancer. This offers another good reason we need to go natural. I always try to go handle any housebug problems using a natural solution. In case you are not familiar with a way to take care of pest control without using health hurting chemicals check out Neem Tree Oil… that’s about as natural as you can get!