I 'm an old/new beekeeper. In 1968, I was at that time living in France, when my uncle passed away, I had, with my aunt, to take care to my uncle's bees (3 Boxes, 2 Skeps w/ supper, and 2 Dadant hives). I did my best for 4-5 years and for some reasons, I had to leave them.
I moved to the US / NJ five years ago. Last March, I met one of my wife's colleagues who has 6 hives (Langstroth of course). I lent him some antique French books I had on apiculture and bought new ones (especially about bee diseases). I asked him where and how he bought his material and bees … and guess what? – I am back to bees and now have a nice hive in our backyard.
I bought a 2 story-hive and a 5 frames nuc at a local bee supplier. On May 6th, my son (6 1/2 years) and I installed the colony from the cardboard nuc to the 10 frames hive (3 w/brood + 2 w/honey from the nuc + 5 frames w/wax foundation). We fed the colony with a 1:1 syrup + Fumidil-B. For almost two weeks, unfortunately, we could see dead larva with chalk brood at the entrance of the hive. So last Sunday, we investigated the hive. Everything seemed to be OK, the queen was there, we saw some larva, nice and white, the number of bees was greater than when we installed them and a lot were young. There were 6 frames of brood, some empty cells. I think it is due to the larva that died from chalk brood. The 4 other frames were partially built with nectar and honey in two of them, so we decided to put the next story of 10 frames of foundation on the first one with a Miller feeder one top of them.
Now that I am done setting the context, my question is “What can I do to stop the chalk brood?” “ Should I requeen now or wait until July?”
Does anybody know what causes the chalk brood? Is it stress or weather or some thing else???

Thank you for your help.