Leviticus 26:20

ותם לריק כחכם AND YOUR STRENGTH SHALL BE SPENT IN VAIN — Behold, if a man does not toil in his field — neither tills, nor sows, nor weeds it, nor clears away the thorns, nor hoes it, and then at harvest time blight comes and strikes it (the field, i. e. destroys that which sprung up of itself), surely it does not matter much (he does not take it to heart). But if a man has toiled — he has ploughed, sown, weeded, cleared away the thorns and hoed it, and then blight comes and strikes it, surely then the teeth of that man become blunt! (a figurative expression for becoming speechless, terror-stricken) (Sifra, Bechukotai, Chapter 5 4). ולא תתן ארצכם את יבולה — This means, the earth shall not yield even as much as you brought to it at sowing-time (יבולה as passive participle with suffix of יבל “to bring”, may denote: that which is brought to it) (Sifra, Bechukotai, Chapter 5 4). ועץ הארץ AND THE TREE OF THE GROUND [SHALL NOT YIELD] — This implies that even from the very earth a curse will rest upon it — that it will not bring its fruits to development at the time when they should develop (Sifra, Bechukotai, Chapter 5 4). לא יתן serves as the verb with what precedes and with what follows — with “tree” and with “fruit”. Thus we obtain a second sense — לא יתן פריו IT WILL NOT GIVE ITS FRUIT — when it does produce fruit, it will cast its fruits (Sifra, Bechukotai, Chapter 5 4). This gives two curses, and so you have here seven punishments in all.

and your strength shall be spent in vain: for your land shall not yield her increase, neither shall the trees of the land yield their fruit.

וְתַ֥ם לָרִ֖יק כֹּחֲכֶ֑ם וְלֹֽא־תִתֵּ֤ן אַרְצְכֶם֙ אֶת־יְבוּלָ֔הּ וְעֵ֣ץ הָאָ֔רֶץ לֹ֥א יִתֵּ֖ן פִּרְיֽוֹ׃