The unpredictable nature of weather makes irrigation a necessity with some crops. How you irrigate can have a dramatic effect on food safety. A number of considerations must be planned for when irrigating crops.

Method of irrigation

With all other risk factors being equal, overhead irrigation poses the most risk of contaminating a crop. Surface irrigation, such as exposed drip tape on top of the soil, is less of a contamination risk. Finally, irrigation delivered in a closed system, such as buried drip tape or drip tape under plastic, poses almost no risk of contamination.

Plant growth stage

If the plant is in a vegetative state or is more than a month from harvest, then there is a relatively low risk of contaminating the crop. If, however, the crop is within two weeks of harvest, or there are fruit present on the plant, the risk of contamination is increased significantly.

Water sources

Municipal and well water sources are the safest in terms of potential contamination. Ponds are an intermediate risk while rivers and streams pose the greatest risk to contamination.

It is of particular importance to remember that risk is a reflection of how easily an existing pathogen can get through to the crop after harvest. Just because a grower utilizes a high risk source, method or plant growth stage, it does not mean that a grower is destined to contaminate the crop. If the water test employed by the grower shows low or no generic E. coli numbers, then there is little chance of contamination.

Understanding irrigation water risks is complex and very specific to a grower’s practices. If you have difficulty with understanding these risks, contact the Agrifood Safety Work Group at gaps@msu.edu or 517-788-4292. To obtain more information about irrigation water risks, ask for guidance document AFSM033-01.