In simple terms, "ruinous effects" means something that badly damages or destroys something else.
Sentences with «ruinous effects»
There were still no winnings at stake — the Vichy government banned professional athletics, citing money's ruinous effect on sport. (sbnation.com)
And to associate Labour, which has twisted and turned to keep Britain out of the euro, with ruinous effect, as well as keeping us out of Schengen, with being pro-European, is absolutely outrageous. (liberalconspiracy.org)
Instead of focusing on Paladino's deficiencies, I ask Mr. Lazio to focus on Mr. Cuomo's much greater deficiencies which will have ruinous effects on NYS residents. (nystateofpolitics.com)