Overhead shelters protect food items and customers from the elements. Shown here is a produce stand at the FreshFarm Market at Dupont Circle in Washington, D.C. on June 12, 2012.

Carol Guensburg

James Smith weighs a bag of produce at his stand, part of the weekly Tuesday market at a U.S. Department of Transportation office in Washington, D.C. on June 12, 2012.

Kris Connor

Bare-hand contact while cutting produce -- especially samples -- increases the risk of spreading disease. Instead, vendors should wear gloves -- not fabric, unless they’re washed after each use.

Kris Connor

Strawberries beckon at the Market Square Farmers Market in Alexandria, Va. Awnings protect food items from the elements on June 12, 2012.

Kris Connor

A worker arranges summer squash for sale at the Market Square Farmers Market in Alexandria, Va. on June 12, 2012. Gloves reduce the risk of contamination between produce and workers.

Kris Connor

A vendor offers samples of seafood spread, warning customers not to double dip on June 12, 2012. But customers might reach for crackers from the containers instead of pouring a few into individual cups.

Carol Guensburg

To reduce food-safety risks, keep hot foods hot and cold foods cold. At a farmers market near the White House, Coulter Farms of Coulter, Pa., offers cheese samples in clearly labeled containers set on ice on June 12, 2012.

Kris Connor

Thomas Pearson of Dunham’s Produce offers fresh peach samples at the Market Square Farmers Market in Alexandria, Va. on June 12, 2012, reportedly the nation’s oldest continuously operating market. Pearson also demonstrates proper handling by keeping samples in a covered container, served with toothpicks to prevent bare-hand contact.

Kris Connor

At a farmers market near the White House, Stephanie Roseman prepares a sandwich for the Fish Scales concession -- and demonstrates safe food-handling techniques on June 12, 2012. Gloves prevent bare-hand contact, and ice keeps condiments cool. The market was about to close for the day, and most of the ice had melted.

Kris Connor

Jeff Hughes rests with his dog, Hartley, and a basket of rhubarb near the Market Square Farmers Market in Alexandria, Va. on June 12, 2012. Many markets forbid pets or restrict them to tight leashes.

Kris Connor

Many farmers markets -- such as this one in Alexandria, Va. -- forbid pets or restrict them to tight leashes. You don’t want someone petting an animal and then touching food.

Kris Connor

Sam Kass, White House assistant chef and an adviser on first lady Michelle Obama’s healthy-foods initiative, often takes school groups to farmers markets or on tours of the White House’s kitchen garden.

Emmanuel Tambakakis