With our 62 year old house came an acre of yard that had not been tended in twelve years. One large problem is a southeast-facing bed of white irises that grow under the canopy of three pine trees. The bed is glorious in the spring until the vines (VA creeper, tie vine, and poison ivy) take over before the blooms are spent and die back at first frost. We tried pulling up the invasive vines by hand, but the root systems are heavily entrenched and I discovered I am highly allergic to the poison ivy. If and when would it be safe to spray a vine-killing product over the whole bed but not harm the irises?