“It’s hard to make predictions, especially about the future.” (Yogi Berra)
Herbicide resistance is easy to predict. Continuous use of any herbicide on extensive areas of land in simple cropping systems (e.g. Iowa corn-soybean rotations) for extended periods of time will selectively favor weed variants with traits conferring resistance to that herbicide and eliminate or reduce susceptible phenotypes of the same species in those fields. Descriptive studies can reveal the extent and locations of the problem. Alternative herbicides and resistance management recommendations can ameliorate the problem (Owen, 2011). A practical short-term approach to the problem could include the following steps:
Describe the resistance problem:
Prediction, step 1: What is
the problem?
Document resistant biotypes in Iowa fields
Prediction, step 2: How bad is the problem?
Document the extent of the resistance problem in Iowa
fields
Solution 1: Recommend alternative herbicides and resistance management
Explaining and understanding the biology of resistance is more difficult. Explaining and understanding the nature of the resistant biotypes (R) is more difficult. Will the problem get worse or better in the future? What is the biological basis of predicting these risks? How do we predict the ecological role a resistant weed species will play, in the absence of herbicide use? Resistant weeds are more than just resistant. All individual weed species fill a specific niche, or role, in weed-crop communities. Herbicide resistance is but one trait important to the weed species in fulfilling its ecological role, its fitness, its threat to crop production. Resistant weeds have evolved other crucial traits ensuring their presence in local cropping fields before selection by new herbicide. The evolutionary past is the key to unlock the future.
What ecological role does R play in the absence of its herbicide?
The answer to this question is important. It is the basis of predicting the risk posed by the resistant population based on the other traits, and the ecology of those traits, that will allow the species to thrive in agricultural fields in the absence of herbicides. Is the resistant biotype fit on its own, without the helping hand of herbicide use? Resistance traits alone will not ensure that a particular weed species will become an unmanageable problem. If R is rare, if it is not well adapted in the absence of herbicide to fill an ecological niche, then the problem may not be as extensive or pose as great a risk. If not common, then control of dispersal of resistant seed may stop it or slow its development such that management tactics will succeed. If R is fit, then it will be found in many fields. Resistance will only make the situation worse. If it is present in many fields its development to be rapid. If it is common, then the synergy between herbicide selection and local adaptation will result in an extensive resistance problem. In this case, resistance management tactics may be much less effective. A logical approach to understanding the problem, and predicting its outcome, could include the following steps:
Explain the resistant problem:
Prediction, step 3: Is
R fit without herbicides?
Determine the non-R traits leading to success in crop
fields
Prediction, step 4: Do other R traits pose a
risk?
Determine the role R plays in crop fields
Solution 2: Develop cropping systems based on the roles weeds play in agroecosystems
Solution 3: Train future weed scientists about the central role evolution plays in agronomy