Rachel running off is not only to protect herself from Marty's criminal connections, but after the accident, the Blue Cat would have lost business and faced investigations and inspections (the latter a major plot line in Season 2).
In the first two seasons, there's a Running Gag where Marty will use Insistent Terminology to say that the cartel he's working for is the second-largest in Mexico. In the third season, the plot is largely driven by the fact that the cartel is losing a war against another. Being only the second-largest has suddenly become pretty important.
Having lured Russ on with promises of love and a fly fishing shop, it's fitting that Petty met his end with a tackle box.
Fridge Horror
In the shot of the horse castration, the horse depicted has no penis and had the operation on the floor of its own stall. No wonder the owner was so horrified - the horse was not only castrated (a sometimes elective or medically necessary procedure - if financially damaging here) but had its penis removed and was operated on in an unsanitary environment, meaning it will likely get infected and/or die (assuming that the "surgeon" even created some way for him to urinate).
It's unlikely that Jonah really needed to murder Mel. Mel broke the law in stealing the cookie jar from the Byrdes' home, so it's not going to be admissible in court if he takes it with him. And even if the Byrdes are more worried about their reputation than getting charged with murder, they could easily claim ignorance and pin the deed on Ruth, since she bought the cookie jar, gave it to the Byrdes, and is now too dead to defend herself.
Considering what Cartels in real life have done to their enemies, including those who have done less than remorselessly murder the son of a Cartel boss, it is almost commendable of Camila to simply shoot Ruth dead rather than kidnap her and put her through Cold-Blooded Torture, do the “Country Matters-to-Mouth” thing she threatened Claire to her or even sell her to Human Traffickers.
