scores of

As you have demonstrated knowledge of, it does mean, in general, a lot. As to around how many that would be, in colloquial usage, I would tend to think that it would depend on the context of the particular field being talked about--in this case, 'growers' (famers/producers). In a field context, I'll argue, where number intensity is high, the word would surely be higher quantity-wise, than when talking about a field where the intrinsic number in the whole set is orginally low. I hope this helps some.

A score is equal to 20. Scores is just used to indicate many, but should be something over two score.

Though these idioms often come from words, like 'score' or 'dozen' which have specific meanings they are indeterminate amounts that hold meanings that can't really be determined from their origins.

As KaiseiJin noted, the context has to be taken into account. For this situation, I would take 'scores' to mean 'a lot.'

If someone were to ask me to put a number on 'a lot', I couldn't really because I don't know the situation well enough. But either of the indeterminates, 'scores' or 'a lot' would satisfy me in my reading of that article.