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Weedy Adaptation

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Weedy adaptation is the consequence of weed evolution over time. Management practices used by farmers select certain weeds to survive, and kill others that don't contribute to future generations. Over time weed populations in a field will change in response to these management practices. This section is all about these changes: adaption, evolution, selection and population shifts.

Weeds change over time, the weeds that produce seed are the only ones that will endure into the future. The changes weeds undergo are called adaptation. Adaption within a weed species-group, species or population comes about in many ways, all of them are directly related to the management practices they encounter and the conditions in the environment. Weedy adaptation can be any morphological, physiological, developmental or behavioral character that enhances survival and reproductive success of an organism. Over long periods of time weedy adaptation results in evolution of that species or group of plants.  Visit the:  Weird & Wild World of Weedy Adaptation.

Weed populations are the adaptive product of long term selection in response to forces in agroecosystems. Certain minimum conditions are required for evolution to occur:
1. Reproduction: A parent plant produces more offspring than can normally survive
2. Genetic variation exists in the population
3. Selection for fitness: "Fitter" phenotypes (among those variable, excess offspring) are more likely to survive
4. Inheritance: The "fitter" traits of those phenotypes are inherited
5. Increased probability of survival of offspring possessing a particular phenotypic characteristic

One of the most important conditions necessary for evolution to occur is for the more fit offspring of a parent plant to survive from among the excess offspring that parent produces. Selection pressure is imposed on these excess offspring by the environment as well as the management practices of the farmer growing crops in that field. The practices that result in selection pressure include the use of herbicides, tillage, crops and crop rotations.

Weed Population Shifts
Weed population shifts are the changes in the individual organisms that make up the population of an locality, often caused by changes in weed management practices.  The bottom line for a farmer, and an individual field, is that because weeds adapt they change. Those practices that controlled weeds in your field this year probably won't provide acceptable weed control in future years. Why? Because what you do today kills those weeds susceptible to your management practices. The few weeds that survive today's management practices are the parents of the weed problems you will have in the future: leaner, meaner, better able to handle what you dish out.  This process has been going on for thousands of years. Every crop grown by humans, in every field, in every year for the history of agriculture has resulted in the weeds you have in your field today.   Let your clutch out and:  Take the Population Shift Tour.

Weedy Adaptation in our Worst Weeds
The most important weed population shifts probably occurred long ago. The worst weeds we have today are the winners of this selection-adaptation-evolution process. Take a while to tour some of those very bad weeds and learn more about what adaptations make them so successful.  Weedy Adaptation in: Velvetleaf, Foxtail Species-Group, and Quackgrass.

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Advanced Topics in Weedy Adaptation

Adaptation of weeds to conditions in agricultural fields takes place on many time scales, from the short-term survival of a herbicide resistant weed to a herbicide as it emerges, through the long term changes within a genus over evolutionary time. Most of the focus in this course is appropriately time scales important to weed management. Below are some advanced topics in weedy adaptation on time scales longer than is probably necessary for weed management. These sections are entirely optional, feel free to explore them.

Plant Speciation | Plant Evolution