The Outer Limits - Season 6 Episode 7
Seeds of Destruction

Macroseed, a cutting edge biotechnology company, chooses the small farming town of Hobson to test and develop TX-40. This is a new genetically- engineered strain of fast-growing corn that, it hopes, will increase yields and make the company millions. Linda, the veterinarian in Hobson, begins to wonder about the safety of TX-40 when Old Man Rivers brings in a dead cat from his field that has horrible mutations, including a giant tumor which sprouts a fifth leg.