Certified GKH Gardening Expert
This could be one of a few things: Overly dry or drought-like conditions, or the result of some type of fungal problem (there are many). First, check that the soil is not too dry and, if necessary, give the plant a good soaking. Also, check the drainage and if newly planted push down on the soil to collapse any air pockets that may be present, as these can restrict the roots from taking up water. You can normally cut away the brown or dead looking growth (should regrow once problem fixed). Treat the plant with a fungicide, like Neem oil, which will also double as an insecticide if there happen to be any pests affecting it as well.