Many of the herbicides used in traditional crop rotations of Montana have long residual activity. That means they can persist for several years after application and cause injury on sensitive rotational crops. With the increasing crop diversity within Montana rotations it is essential to maintain good herbicide records. Most herbicides lose activity by degrading.
Herbicides degrade in the soil by either chemical or biological processes.
Factors that increase the persistence of herbicides are factors that will decrease rate of degradation. Critical factors include pH, moisture, and temperature. Because Montana has a dry climate and short growing season herbicide degradation generally takes longer than in warmer and moister areas of the country. Refer to herbicide labels to determine rotation restrictions following application of certain herbicides. Rotational intervals for several herbicides and crops have been provided in the following table, but are no substitute to thoroughly reading the herbicide label.