Dust with wood ash or rock phosphate. Plant catnip, tansy and radishes nearby. Use row covers. Put plants on trellises to keep them off the ground. Beetles skeletonize leaves, leaving them shredded and dried out.
Plants eventually die.
Hand pick beetles. Keep garden clean and free of debris, especially after harvest to prevent egg-laying. Plant early to miss the insect's season. Plant nasturtiums, marigolds, savory and garlic nearby. Plant resistant varieties.