Does anyone know what is going on here, about a quarter of my plants have developed this. They are outside now and have been for a month but were started in a GH in fiber pots. They had a couple of days of intense heat in GH >120 degrees F. The white powder is from a dusting. The majority of the plants are normal just half of their tips. I have a soil ph meter on order along with some lime that will get here in a couple of days.