أَتُنْكِرُ أَثَرَهُ وَأَنْتَ تَرَاهُ فِي الطِّبِّ وَالزِّرَاعَةِ؟
Do you deny its effect while you see it in medicine and agriculture?
Wa-anta tarāhu is a nominal circumstantial clause linked to the main utterance by the circumstantial wāw and pronominal reference. It presents the denial as occurring in the very circumstance of seeing evidence.
Not every wāw simply joins two independent propositions. Here the circumstantial reading qualifies the main act and intensifies the reproach.