Guten Tag Helmut! I will give it a try. But we have to dig a bit.
I hope you have already some knowledge in south-east european history,
else it might get confusing.
Kukurutz is a term used for corn in Austria, and as you pointed out, used by german settlers in
south east europe. The term is used to a lesser extend also in southern germany.
Also many slavic languages use similar terms for corn. Like kukurydza in polnish, russian кукуруза,
hungarian kukorica, and so on.
From what i understand the term has its origins during the time of the Austro-hungarian empire.
There was an uprising in hungary 1671-1711 by a group called Kuruzzen, against the ruling
austrian Habsburg monarchy.
The term Kuruzzen goes back to the hungarian term Khurudzs, which means insurgents.
This fell in the same time period as the Habsburg great war against the ottoman empire from 1688-1699 ,
and the Kuruzzen allied with the Ottomans during the failed ottoman siege of vienna 1683.
Keep in mind that many slavic nations were allied with the Austro-hungarians at that time,
such as poland (which had a huge role in the vienna defence success), russia, croatia, and some more,
and fought against the ottomans and their puppets.
Why corn was called Kukurutz by the hungarians and austrians, and quite similar by slavic allied nations,
and named after these insurgents, there are a few explanations.
Some argue its because the ottoman troops brought corn with them, a rarer food back then
for austria, but huge scale grown by the ottomans, and given by them to their insurgent allies, the Kuruzzen.
Also they brought corn as supplies for their attempted vienna siege in 1683.
Some say, its also because the ottoman officers hat, the Fez, looked a bit like a corn cob with its pom pom like cord.
So kukurutz means basically "corn of the Kuruz(insurgents)".
Turkish was the dominating ethnicity in the ottoman empire (next to arabs),
and a mashed paste of corn is called until today turkish mash (Türkensterz) in austria, while the term turkish flour is used more rarely and outdated for corn flour.
Further showing the connection between the naming of corn and its products, and the ottoman/turkish forces and their insurgent allies during the austrian-ottoman war.
Hope you can make some sense out of these information. Greets!