From mid-May through October, the hillside below the left side of Boulder Slips is covered in poison ivy. It is difficult to avoid no matter how you approach the climbs. Better to climb somewhere else during this time. Routes on the center and right side of Boulder Slips are not affected.
From November to early May, the poison ivy is dormant, but watch out for the plants with little light-green berries -- these are poison ivy bushes. Avoid them and you should be OK to climb on the left side of Boulder Slips at those times.