I'd figure: bulb is dead ==>> plant cells in bulb are dead ==>> virii in the bulb can't reproduce (since that requires living cells). If (say) they know that t

I'd figure: bulb is dead ==>> plant cells in bulb are dead ==>> virii in the bulb can't reproduce (since that requires living cells). If (say) they know that the disease is infectious (to nearby tulips) mostly later in the course of infection, then "catch early, kill, leave in place" could make perfect sense.