The results suggest that the F1 plants from reciprocal crosses were all resistant to glyphosate suggesting that the glyphosate resistance is a nuclear trait in kochia. Furthermore, florescent in situ hybridization analysis was performed on glyphosate-resistant and –susceptible kochia chromosomes. The results indicate for the first time that the EPSPS copies are arranged in tandem and are located close to the telomere region of the chromosomes. These results suggest that the EPSPS amplification may have occurred as a result of unequal recombination. We have also tested kochia populations from Kansas for multiple herbicide resistance. The results suggest that these populations are at least resistant to more than 2 modes of action of herbicides. Multiple herbicide resistant kochia is a major challenge for kochia management.