What is the ruling on selling fertilizers and medicines for grapes, most of which are used in the production of wine?

Assisting in sin is forbidden. The meaning of "assisting" is when the sin is directly brought about by the act of the assistant. This occurs through the intention of assisting, explicitly stating it, or when the use of the object is unequivocally for sin, admitting no other possibility. However, if the sin is not directly brought about by the act, then it is not true assistance, but rather a cause. If a cause instigates and encourages sin, then it is forbidden. If it does not, but is merely a direct and proximate means, then it is reprehensibly disliked (makrooh tahriman). As for a remote cause that requires an elaborate process to turn into a sin, it is mildly disliked (makrooh tanziheen). Therefore, selling fertilizers and medicines to someone who sells their crops to someone who presses them into wine is considered a remote cause, and there is no sin in it.