My roommate is from mainland China and only has anecdotal stories to share, but I'm curious as to the state of Soviet crop maintenance as opposed to the States, which was prevalent in the late 70s to now.
Yes. While I do not know a lot of the specifics about what chemicals were used for crop maintenance by the Soviets, the USSR certainly did employ crop-dusting aircraft rather extensively. The Antonov An-2 for example was actually nicknamed the "Kukuruznik" - which loosely translates as "corn crop duster". It first flew in 1946, and was used primarily as both a utility/transport and crop-dusting aircraft.
Later, in the 1970s and 80s, the Polish-made PZL M-15 Belphegor was a jet-powered aircraft that was designed specifically for crop-dusting work, and it saw a lot of airtime over Soviet farmland. The Soviets used them quite a bit to dust their large-scale state-owned Sovkhoz and Kolkhoz farm collectives with pesticide and fertilizing agents.