Weed killers used extensively today in an attempt to offset the great agricultural losses caused yearly by weeds. Some writers would almost lead us to believe that weeds are on their way out as a result new weed killers.
New Herbicides
It is true that the new herbicides are a little short of being miraculous but valuable as they are, we can’t count the weeds out. In spite of the recent scientific advances in the control of weeds, they will probably be here as long as man.
Weeds are plants that are adapted to areas disturbed by man – cultivated fields, fence rows, barnyards, lawns, and the like and often compete directly with our cultivated plants.
Weeds arose in great numbers when man first began to till the soil, and throughout the history of agriculture, man has been combating weeds.
Controlling Weeds
Why weeds are difficult to control is not hard to understand.
The seeds of many weedy plants will germinate after having been buried in the soil for 50 years or longer.
Some of our weeds produce more than 100,000 seeds on a single plant. Many weeds, dandelion, for example, have very efficient means of transporting their seeds to new areas.
There is little wonder that man is constantly seeking new ways of controlling these pests.
Competing with Cultivated Plants
Not only do they compete with cultivated plants for water, light, and minerals, but some weeds are also poisonous or possess other objectionable features. The great majority, however, are relatively harmless, and many are even attractive.
Let us assume for a moment that the new weed killers were to eradicate all of the
weeds in a given area.
Burying Old Weed Seeds
In no time at all old buried weed seeds would germinate or seeds from weeds in adjacent fields would invade the area devoid of weeds.
Or let us make an even more unlikely assumption that all the weeds throughout the world would be eliminated by some means.
What would happen?
Man would continue to create disturbed areas – by plowing, road building, and other means.
Habitation of Wild Plants
These habitats would be available for colonization by other plants – our so-called wild plants would soon exploit the unoccupied niche – and we would soon have a whole new set of weeds evolving from wild plants.
Of course, the realization of the above assumptions is highly improbable, for whenever weed sprays arc used not all the plants are killed.
The weeds which survive may be more resistant to the spray than their relatives, and they, of course, will mature seed and produce offspring so that in time a race of weeds resistant to the ordinary concentration of weed killers and the other herbicides may come into existence.
Using of Hydrocyanic Gas
Two examples from the animal kingdom will serve to illustrate this point. In the citrus orchards of southern California, hydrocyanic gas was used to control the red scale, which causes serious disease in the citrus plants.
However, it was found after a number of years that the ordinary concentrations of gas were not sufficient to control these mites.
Either there had been emigration of a resistant race of red scale from some other region or the survivors from the previous sprayings had been able to build up a resistant race. The same thing has happened more recently with DDT control of flies.
Method of Controlling House Flies
At first, DDT provided an efficient method of controlling house flies, but DDT became relatively ineffective after a while in many areas. Races of flies resistant to DDT have come into being.
This same sort of thing is happening to weeds as was reported by Glen Viehmeyer of the University of Nebraska.
This is not at all surprising, for although a group of weeds, pig-weeds, for example, may appear identical to us, it will be found.
If the plants are studied critically, there are many minor differences from plant to plant – both in appearance and in their reaction to the environment.
Variations of Weeds
These differences or Variations have arisen through mutations, or sudden changes in the germplasm, and among these mutations, there may be some which make the plant more resistant to weed sprays.
Man, by spraying the weeds, acts as a selective influence eliminating the “weak” or non-resistant plants and leaving the “superior” or resistant plants which in time can build up a race of weeds that can tolerate heavy spraying.
This pattern follows well-known evolutionary laws, and it can be seen that man himself is helping to create new races of weeds.
I do not want to seem a pessimist – we should continue to use any new methods of weed control because they are extremely useful – but the weeds are far from being on their way to extinction.
Loving the Weeds
We may never learn to love the weeds, but we must learn to live with them.
It is possible, of course, that in the distant future some new method of agriculture may be developed in which the weeds would find themselves at a great disadvantage. This is hard to imagine.
It is my opinion that weeds are here to stay.
44659 by Charles B. Heiser, Jr.