White substance on butterfly bush
Appeared over the winter. I thought maybe a fungus or mildew - it looks similar to the white substance that sometimes appears on mulch that has been damp for an extended time. Nothing else around seems to be infected. Should I cut it down to the soil level. Thanks.
Yes, this looks like a type of fungal decay. Buddleja is susceptible to several types of fungal diseases. These shrubs can be cut to the ground in the spring when dormant before new growth starts to emerge. This looks like significant decay, but if there are healthy buds at the base of the plant, it may come back for you.
Please keep in mind that butterfly bushes are now invasive in wilderness areas of Maryland and they are no longer recommended for planting. https://extension.umd.edu/hgic/topics/butterfly-bush
If you have the opportunity to replace the plant, please consider one that is native and adapted to Maryland conditions. There are many good choices that are are attractive and support butterflies. https://extension.umd.edu/hgic/topics/native-plants