Dry soil conditions can enhance persistence of herbicides such as atrazine. Kentucky has had dry seasons in the past, yet atrazine injury to rotational crops was seldom an issue. Having said that, the risk of crop injury due to atrazine carryover is still an issue that we need to consider on a case by case basis.
The risk will be reduced if atrazine was applied early spring and had some rain to move into the soil profile. Prolonged periods of dry soil will enhance persistence and increase the chance of injuring rotational crops. If weather conditions improve and we have a mild and wet fall and winter, then the risk of carryover to spring planted crops will be reduced. Using high rates of atrazine will increase the risks. Atrazine may dissipate more rapidly in no-till compared with tilled conditions. High soil pH (pH >7.0) will increase atrazine persistence.
The sensitivity of the rotational crop is another factor to consider. For example on a sensitivity scale from “more sensitive” to “less sensitive”: ryegrass = oats > wheat = alfalfa >> soybean >> sorghum > corn. UK Regulatory Services still runs chemical analysis of atrazine and simazine (Princep). Keep in mind the interpretation of the results is based on tobacco only.
The bottom line is that the grower accepts the risk of injury if he chooses to not follow the label. The following are a few of the AAtrex label statements (applicable to our region) regarding rotational crops.
- Do not rotate to any crop except corn or sorghum until the following year.
- If applied after June 10, do not rotate with crops other than corn or sorghum the next year or crop injury may occur.
- Do not plant sugar beets, vegetables (including dry beans) spring-seeded small grains, or small-seeded legumes and grasses the year following application to injury may occur.