Weed biology is ecology and evolution. This is a graduate level course in the ecology and evolutionary biology of weeds. It has been said that nothing in biology makes sense unless seen in the light of evolution. Our goal is to make sense of weed biology, therefore we need to study the factual basis of weed behavior (e.g. how weed phenotypes behave during their life history) as well as the important, inherent, components of agricultural fields that form plant community structure. For these reasons the approach taken in Agronomy 517 is focused on these big questions:
Why do we have weeds?
Why do we have the weed species that we do? (And not others)
Why do these weeds look and behave as they do?
How did the weeds we have get to be the way they are?
What is the basis
of future changes in weeds?
What I hope you get
from this course is the WHY & WHAT of weed biology. Accumulating facts
about weeds is important. But what do you do with these facts to help you
understand what will happen in the future? how do you manipulate the
weeds biology to achieve management goals? how do you explain new
weeds? how do you understand invasion biology?
This course will emphasize why weeds are the way they
are by means of a mixture of ecological-evolutionary theory and agronomic observations of weed behavior.
The "What" (facts) are on the web, in your
experience, and in our course readings. The "Why" will be revealed through understanding how
evolution and opportunity space drives agro-ecosystems. I want you to have a dynamic framework in your head at the
end of the course to guide you in the future.
A toolkit, a way of looking at new weed phenomena in agroecosystems,
a way to understand why these new things occur, a way to understand the
fundamental forces in nature that cause these things to happen.
Knowing the "Why" will allow you to integrate new
observations with what you already know when the course is done (I hope).
The 517 course in a nutshell: 5 components of "Why"
1] Opportunity space: cropping systems create opportunity spaces by leaving unused resources in local fields that are frequently disturbed (e.g. tillage, herbicides)
2] Weeds invade these opportunity spaces by means of dispersal, followed by colonization, followed by enduring occupation of the field
3] Weed biodiversity provides diverse plants with traits well adapted to seize and exploit these opportunity spaces, which become locally adapted and improved over time by means of natural selection and adaptation
4] Weedy traits are expressed at optimum times in the life history of the plant as the agricultural season unfolds such that they maximize their fitness in a plant community
5] Agricultural plant communities assemble and interact with each other based these traits
Why do we have agricultural weeds? The first principle of weed management
is "The Weeds Always Win". The harder we try, the better they
get:
Why do the weeds always win? The bottom line is: because weeds adapt and change and get better. No sitting around and whining about how unfair life is. Over evolutionary time they have encountered everything nature has to offer. They have died in untold bazillions. The survivors are the winners. Weed biology and ecology is the story of their success. In this course we will learn about the processes and outcomes of this ruthless adaptation to adversity.
Weeds are winners because weed management systems fail. They fail because our current cropping systems create an agricultural "vacuum" of unused resources. Monocultures, and simple rotational systems that behave like monocultures (e.g. corn-soybean), leave unused space, light, water and nutrients. Our homogeneous crop cultivars are not very competitive with weeds. Trends in the intensification of our cropping systems and economic forces have led to a simplification of cropping system diversity:
