Disease resistance is a connuum that ranges from complete suscepbility to immunity. Bronze leaf disease (BLD) is a fungal disease, spread by wind‐blown spores, that has decimated stands of Swedish aspen and Tower poplar across the prairie provinces.

Fortunately a new contender has emerged in the bale against BLD. ‘Guardian’ columnar aspen presently offers a high level of resistance to BLD. When ‘Guardian’ was grown beside suscepble Swedish aspen under Manitoba nursery condions, the difference in disease response was obvious.