Hefker produce: Is Hefeker produce exempt from Teruma and Maaser?
All produce which did not have any ownership upon growth [i.e. was Hefker] is exempt from Teruma Umaaser. [Thus, fruits and vegetables which grew on an ownerless/Hefker tree or plant are exempt from Teruma and Maaser. This applies whether one plans to eat the fruit or sell it.] However, one who plants in a Hefker field, the produce that grows is obligated in Teruma and Maaser.
If one picked many fruits from Hefker [such as for the sake of selling it], is it obligated in Terumos and Maasros?
If one collects a large amount of Hefker produce, and makes a mound of it in the city or field, then he is to remove Teruma Umaaser [without a blessing] due to Maras Ayin.
 Michaber Y.D. 331:16; Hakashrus 15:14
 Brachos 40b; Sota 43b; Ravaad Terumos 2:12; Omitted in Rambam [however, see Rambam Terumos 12:9 regarding Peah]; Rav Poalim Y.D. 4:40; Derech Emuna ibid 20; Chazon Ish Shevi’is 2:5; Rav Yaakov Yosef; Rav Yaakov Tupik in Kedushas Ha’aretz p. 57
 As its only obligated due to Maras Ayin. [Rav Yaakov Yosef]