Monsanto got slammed pretty good by both fitch and S&P so I wouldn't say their balance sheet was pristine. Being that Monsanto is going into the market right now a scoop up around $6 Billion of shares (10% of the company) tells me that they need these shares off the market to meet the eps numbers. They also risk buying at an inopportune time.
Their long rates don't seem like a bargain in my opinion.
$500 million in senior notes that mature in 2017 and bear interest at a rate of 1.150%,
$500 million in senior notes that mature in 2019 and bear interest at a rate of 2.125%,
$500 million in senior notes that mature in 2021 and bear interest at a rate of 2.750%,
$750 million in senior notes that mature in 2024 and bear interest at a rate of 3.375%,
$500 million in senior notes that mature in 2034 and bear interest at a rate of 4.200%,
$1 billion in senior notes that mature in 2044 and bear interest at a rate of 4.400%, and
$750 million in senior notes that mature in 2064 and bear interest at a rate of 4.700%.