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1901 Youth's Companion 31 Oct 573 NV, The bears increased their threats and yaggerings until the little cañon roared with the horrid noise. 1917 in 2007 (acc) Lexis–Nexis Legal Research State Case Law: KY (Internet), He heard a conversation between the two which he terms   “yaggering.” It is not explained what he means by that term, but we   suppose it was some general talk passing between the two such as occurs   between persons more or less intoxicated. 1922 Cobb Kinfolks 44 KY, Times I would sull up like a possum while / The travelers would yagger to theirselves. 1944 PADS 2.22 sAppalachians, Yagger [jægÉš].   .  . To cavil. “Oh, I wouldn't yagger about a little thing like that.” 1949 Hornsby Lonesome Valley 8 eKY, Do this! This! This! Do that! That! That! Yagger, yagger every minute of the time. Ibid 82, Crit had a good right to quarrel about Lucindy that morning after the way she yaggered at him in front of Johnny. Ibid 147, When girls got together they cut up worse than a bunch of pups   romping in the yard, hanging on to each other and yaggering. 1978 Hiser Quare Appalachia 181 eKY, I went to bed .  . , a-leavin the three women a-settin in front of the   far a-yaggerin like women folks will at ain't seed one another in a   spell.

 

And I finally found this from the English dialect Dictionary archived https://archive.org/stream/englishdialectdi06wriguoft#page/562/mode/2up

Yaggle -meaning to argue or quarrel...would have sworn it was german.