The 1841 British edition accidentally dropped the and between the two prepositional phrases headed by upon, giving the asyndetic construction “upon the land / also upon your riches”. The 1849 LDS edition restored the correct reading with the and. Undoubtedly, the original text had the and here. Such asyndetic conjoining of prepositional phrases is unexpected but not impossible in the Book of Mormon text. Elsewhere in the text there is one instance where two upon-phrases are conjoined without any conjunctive element:
𝓞 is not extant for Alma 5:53, so it is possible that originally there was some conjunctive element before “upon your riches” that was somehow lost during the early transmission of the text. Note that other conjuncts involving riches and vain things always have an explicit connector, usually and:
Nonetheless, there is evidence in the earliest text for the occasional asyndetic construction (consider, for instance, the phraseology without the expected and in Mosiah 22:8: “thus we will depart with our women and our children / our flocks and our herds into the wilderness”). The critical text will, of course, maintain the syndetic reading with the and here in Helaman 13:23 (“upon the land and also upon your riches”) since this is the reading of the earliest extant text.
Summary: Maintain the conjunction and that connects the two upon-phrases in Helaman 13:23: “a curse should come upon the land and also upon your riches”.