Describe the resistance problem:
Prediction, step 1: Document resistant biotypes in Iowa fields
The first step in predicting resistance in Iowa crop fields is to document what specific weed species are resistant to the introduced herbicide. The first herbicide resistant weeds documented in Iowa were those resistant to the s-triazine herbicides, predominantly atrazine: kochia (Kochia scoparia) in 1987, common lambsquarters (Chenopodium album) in 1989, Pennsylvania smartweed (Polygonum pensylvanicum) in 1991, and giant foxtail (Setaria faberii) in 1993.
Dekker, J., R. Burmester, K. C. Chi and L. Jensen. l987. Mutant Weeds of Iowa: s-triazine resistant plasids in Kochia scoparia. Iowa Journal of Research 62:l83-l88.
Dekker, J. and R. Burmester. l989. Mutant weeds of Iowa: s-triazine resistant plastids in Chenopodium
album L. Journal of the Iowa Academy of Science 96:6l-64.
Dekker, J., R. Burmester and J. Wendel. l991. Mutant weeds of Iowa: S-triazine resistant Polygonum
pensylvanicum L. Weed Technology 5:211-213
Thornhill, R. and J. Dekker. 1993. Mutant weeds of Iowa: V. S-triazine resistant giant
foxtail (Setaria faberii Hermm.). Journal of the Iowa Academy of Science
100:13-14.
Describe the resistance problem:
Prediction, step 2: Document the extent of the resistant problem in Iowa fields
The next level of prediction is practical:
How extensive is the resistance problem?
How many locations within the region does the
resistant weed infest?
How numerous are these individual populations
in particular local fields?
These questions cannot be answered a priori. The most reasonable way to answer them is to conduct a demographic survey among growers and local weed experts and discover the extensiveness of the problem. This demographic, descriptive, approach is expensive and takes time. The effort is worth it because the consequences to farmers of not knowing is not acceptable.