This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. Also, this is a specific month, so it uses the がつ reading.
I went to Tokyo in June.
I will buy two katanas in May and test them at the Tofugu office in June.
The weather for June is cloudy with a chance of meatballs.