The importance of herbicides, biotechnology and evolved herbicide

resistance in weeds on crop production – the need for continued innovation

Micheal D.K. OwenUniversity Professor

Agronomy DepartmentIowa State University

Introduction• Weed management tactics, in a general

sense, have not changed appreciably in several decades– Tactics include cultural, mechanical, biological

and herbicidal• Specific tactics however have seen many

changes reflecting not only technological improvements but also addressing social and economic considerations

Introduction

• Despite the fact that evolved resistance to herbicides has been a concern for four decades, new resistances have tipped the cart

• There are a number of problems in managing herbicide resistant weeds– Grower knowledge– Time management– Economic concerns– Lack of new herbicides

Evolution of row cropweed management

1900 1920 1940 1960 1980 2000 2010

Cultural + Chemical + mechanical mechanical Chemical

New herbicides

What new herbicides?

New herbicides

• No truly new herbicides have been introduced within the last several decades

• Recent “new” products represent existing herbicide groups

• Most are introductions of generic materials by different companies and/or in different pre-mixtures

• The need for new herbicide “sites of action” is critical

New GE crop traits

• The HG 4 traits are now or soon will be commercially available in the US

• Commercial introduction will likely be slow and deliberate

• HG 27 traits are likely several years off• Are new GE crops the answer to current

herbicide resistance in weeds?

Charles Darwin Alfred Russel Wallace

Weed “resistances”

• Weeds with evolved resistance to herbicides is the most widespread pest issue– Waterhemp (Groups 2, 4, 5, 9,14, and 27)– Horseweed/marestail (Groups 2 and 9)– Giant ragweed (Groups 2 and 9)– Palmer amaranth (Groups 2, 5, 9, 14, and

27)• Weeds have also adapted to tillage systems

and other mechanical control practices

Grower perception of herbicide resistance

The reality of herbicide resistance

Considerations

• Most populations are in transition – from primarily sensitive to resistant

• A majority of the fields are not “train wrecks” but rather scattered plants or pockets of weeds

• If observed and appropriate diverse management is undertaken, the problem(s) will be mitigated successfully

The key to herbicide resistance management: Many little hammers

seedbed prep tillage Cover crops

Post-plant tillage Field border management

“Ideal” Integrated Weed Management

Cultural

Herbicide

Herbicide

Cultural

Current Future

Community-based programs to manage a “common pool” resource

• “Top down” weed management information has not been successful

• There has been success with “bottom up” programs (e.g., bollworm in cotton)

• Pilot programs are being considered in several crops

Conclusions

• Diversity of tactics is key• Innovation in technologies is nessary• Development of new herbicide sites of

action is critically important• Agriculture must take a longer-term

management perspective• Use all available tactics

Questions?