Question
I live about 100 miles south of Atlanta. I had 12 knockout roses die of chemical burn last year when I sprayed them with Carbaryl(the insecticide I was using to treat Japanese Beetles)in the heat of the day. I planted new roses this spring (in the same holes)and the first bloom cycle was amazing, but since then there has been only minimal new foliage and no new blooms. I'm afraid they might die again. Is it possible that the soil is still contaminated in some way. It's a fairly sandy soil in a raised bed. What do I need to do to save these roses?

Answer
Carbary is an impressive insecticide and with insecticides there is always some residue but Carbary effects in the soil, are usually gone in about 2 months time. Spraying in the heat of the day is a no no as you have found out, but I don't think that it is the insecticide that is causing your rose problems. Now having said that I am going to contradict myself. I get loads of questions about Knock Out roses and it is becoming very clear to me that although this is supposed to be a miracle rose, they simply will not tolerate some chemicals. Many people have literally killed their Knock Outs with something as simple as a fungicide. So perhaps they are re-acting to the insecticide. I just think I would have got more complaints about Carbary or Sevin , damaging their roses. Another thing that Knock Out son't like and will die back from, is planting on a hot day. They don't seem to be able to get past the effects of the heat when just planted. If you live in an area that gets hot weather in the summer, then sandy soil can actually heat up rose roots to the extent that they  go under stress and do what you have described. Sandy soils really benefit from a mulch of any kind you can get in your area. Roses love and do best with cool, damp roots. If you are having hot weather, then that will be the reason your roses are not doing well. Water them daily and make sure the soil around them is always damp not wet just damp. They should start to perk up and make new growth towards the autumn cooler weather.