John Gill Commentary Deuteronomy 28:38

"Thou shalt carry much seed out into the field, and shalt gather little in; for the locust shall consume it." — Deuteronomy 28:38 (ASV)

You shall carry much seed into the field
And sow it plentifully; this and what is said in some following verses plainly refer to them while in their own land, before carried captive, and not to their present case and circumstances:

and shall gather [but] little in at harvest ;
little springing up, or not coming to perfection, being blighted and blasted, and so yielded but a small crop; see (Haggai 1:9) ; and chiefly for the following reason:

for the locust shall consume it ;
which is a great destroyer of the fruits of the earth; see (Joel 1:4) .