Input Source Verification Letters for GAPs: What do you need?

Some Good Agricultural Practices audits require growers to include a letter from suppliers verifying steps have been taken to limit biological, chemical and physical contamination. This sample letter will help ensure you have effective verification letters

The theory behind due diligence in food safety for produce is being able to track the produce one step forward and one step back. In the case of growers, this one step back is all the input suppliers you purchase inputs from. Some GAP audits only require that you have a letter from these suppliers stating that the supplier took all precautions necessary to limit contamination of the input to ensure food safety. Other audits require that a grower only buy from sources that are themselves GAP-certified. Still others do not require a full input source verification. When attempting to meet audit standards, it is important to find out exactly what, if any, input source verification is required by your audit.

Below is a sample letter from a transplant supplier to the grower for his GAP Manual. Some GAP audit schemes may have different requirements, so be sure to check with the audit company prior to obtaining an audit. The supplier may need to be GAP-certified in order to make a particular auditor happy with the input supplier.

Sample letter

To Whom it May Concern,

Agri-Sprout supplies transplants for Fuller Green Farm. Agri-Sprout takes all precautions necessary to limit contamination of transplants with food borne illness pathogens, physical contaminants, pesticides and excess chemicals. We ensure this by (CHOOSE ANY OR ALL THAT APPLY: regularly testing irrigation water/using drinking water for irrigation/chlorinating water prior to use.)

We train our employees and our supervisors in proper pesticide use and food safety practices. We read and follow all pesticide labels to minimize pesticide contamination. We limit excess fertilizer use beyond that needed for optimal transplant growth. We monitor all shipping containers and trucks to ensure that they pose no contamination risk as well.


Jack Stalk, Vice President of Sales

Other items that may be included in an input source verification letter are enumeration of company policies on hand washing, illness and injury and restricted behaviors; seed and potting mix substrate sources; monitoring of water distribution systems; and any potential animal activity.

Growers who have difficulty tailoring GAPs (Good Agricultural Practices) to their farm are welcome to contact the Agrifood Safety Work Group at or (517) 788-4292. To obtain more information about obtaining input source verification letters, ask for guidance document AFSM005-01.

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