I was reading some period stuff on the Landjahr just now and was reminded of this excellent thread. I came across a couple of dates which confirm the dates given by Widukind earlier on. Although there is no confirmation on whether there was a male and female Landjahr triangle (first pattern) I thought the info would still be useful.
In the original law which introduced the Landjahr on the 29th of March 1934 it is stated that the boys and girls were to wear the Landjahr patch which had been created by the Ministry for Sciences, the Arts and Education. This must be the black one. As I say, there is no mention of different triangles for males and females but certainly by the 20th of July 1935 the black version had been replaced by the green version as the green one is clearly mentioned as being in use in the 'Dienstanweisung für das Landjahr' published on that date.