Are marigolds pest free?
While marigolds are seldom bothered by insects and diseases, they are not problem free. Spider mites can devastate marigolds in hot, dry weather. Grasshoppers can also cause considerable damage. Aster yellows is an occasional disease problem. Aster yellows is caused by microorganisms called phytoplasmas. The disease is transmitted from plant to plant by sap-sucking insects, such as leafhoppers. Marigolds infected with aster yellows are stunted, yellow-green in color, and their flower buds fail to open. Infected plants should be dug up and destroyed.