[Thomas60]

Strong negatives force things to be done, then often people will find a way to escape such future situations (ergo your unjust treatment)
Strong positives redirect already focused minds to achieve better.
As a whole, as long as you have a healthy dose of mild positives... meet standard negative incentive procedures. Then productivity seems primarily based on how close and often you can make people think about behaviours that make them believe they are performing or can perform well and empower them to show others of their value. Reminding, congratulations, upside and downside opinion sharing, tying results to actions.

 

[Thomas60]

Explain what's not happening, what needs to happen, what will happen if things don't change, but also acknowledge the work you are satisfied with. When it's time to reevaluate, even if the improvement is small, acknowledge the improvement as positive, but encourage further improvement. Offer incentives to keep the improvement going if it can be applied to the situation. Have something set in place to use as a consequence for those not meeting expectations, but always start with a verbal or written warning (unless it is something serious that requires more than a warning).

At least, that's how I would do it.

Seems to be a case of 'lead from the front', 'manage from behind'.