[4] After graduation, he started a career in risk arbitrage and option trading on Wall Street, has worked for gourmet specialty store Citarella and acted as a provisioner for Dean & DeLuca.

[2] Karp is a member of the "extension advisory panel" for RosBREED, an organization dedicated to improving rosaceae crops through marker assisted crossbreeding.

[11] Karp has written several articles on the availability of the mangosteen in the United States, due to fears they harbor the Asian fruit fly.

He wrote articles in the New York Times announcing the renewed U.S. law on July 23, 2007, when irradiated imports from Thailand were allowed upon USDA approval,[12][13] and one following its trade at the local markets.

[14] David believes the greengage plum is the most delicious fruit on the world,[3] and traveled to Moissac, France (its primary center of cultivation), to investigate it.