We are not told the specific nature of the curse. But Haggai 1:1–15 might shed some light on this curse. In the first chapter of Haggai, God cursed his people because they failed to contribute towards the rebuilding of the temple, though they themselves lived in fine houses. In that context, God curses them with a curse that corresponded to their sin. The Lord cursed his people with drought and famine (Haggai 1:9–11; Leviticus 26:18–20).
9 You are cursed with a curse, for you are robbing me, the whole nation of you.